<s>
The	O
TRS-80	B-Device
Micro	B-Architecture
Computer	I-Architecture
System	O
(	O
TRS-80	B-Device
,	O
later	O
renamed	O
the	O
Model	O
I	O
to	O
distinguish	O
it	O
from	O
successors	O
)	O
is	O
a	O
desktop	O
microcomputer	B-Architecture
launched	O
in	O
1977	O
and	O
sold	O
by	O
Tandy	O
Corporation	O
through	O
their	O
Radio	O
Shack	O
stores	O
.	O
</s>
<s>
The	O
name	O
is	O
an	O
abbreviation	O
of	O
Tandy	O
Radio	O
Shack	O
,	O
Z80	B-General_Concept
 [ microprocessor ] 	O
.	O
</s>
<s>
The	O
TRS-80	B-Device
has	O
a	O
full-stroke	O
QWERTY	O
keyboard	B-Device
,	O
the	O
Zilog	B-General_Concept
Z80	I-General_Concept
processor	O
,	O
4	O
KB	O
dynamic	O
random-access	O
memory	O
(	O
DRAM	O
)	O
standard	O
memory	O
,	O
small	O
size	O
and	O
desk	O
area	O
,	O
floating-point	B-Algorithm
Level	B-Language
I	I-Language
BASIC	I-Language
language	O
interpreter	B-Application
in	O
read-only	B-Device
memory	I-Device
(	O
ROM	B-Device
)	O
,	O
64-character	O
per	O
line	O
video	B-Device
monitor	I-Device
,	O
and	O
a	O
starting	O
price	O
of	O
US$600	O
(	O
equivalent	O
to	O
US$	O
in	O
)	O
.	O
</s>
<s>
A	O
cassette	B-Device
tape	I-Device
drive	O
for	O
program	O
storage	O
was	O
included	O
in	O
the	O
original	O
package	O
.	O
</s>
<s>
While	O
the	O
software	O
environment	O
was	O
stable	O
,	O
the	O
cassette	O
load/save	O
process	O
combined	O
with	O
keyboard	B-Device
bounce	O
issues	O
and	O
a	O
troublesome	O
Expansion	O
Interface	O
contributed	O
to	O
the	O
Model	O
I	O
's	O
reputation	O
as	O
not	O
well-suited	O
to	O
serious	O
use	O
.	O
</s>
<s>
An	O
extensive	O
line	O
of	O
upgrades	O
and	O
add-on	O
hardware	O
peripherals	O
for	O
the	O
TRS-80	B-Device
was	O
developed	O
and	O
marketed	O
by	O
Tandy/Radio	O
Shack	O
.	O
</s>
<s>
The	O
basic	O
system	O
can	O
be	O
expanded	O
with	O
up	O
to	O
48	O
KB	O
of	O
RAM	O
(	O
in	O
16	O
KB	O
increments	O
)	O
,	O
and	O
up	O
to	O
four	O
floppy	B-Device
disk	I-Device
drives	I-Device
and/or	O
hard	B-Device
disk	I-Device
drives	I-Device
.	O
</s>
<s>
By	O
1979	O
,	O
the	O
TRS-80	B-Device
had	O
the	O
largest	O
selection	O
of	O
software	O
in	O
the	O
microcomputer	B-Architecture
market	O
.	O
</s>
<s>
Until	O
1982	O
,	O
the	O
TRS-80	B-Device
was	O
the	O
best-selling	O
PC	O
line	O
,	O
outselling	O
the	O
Apple	B-Device
II	I-Device
series	I-Device
by	O
a	O
factor	O
of	O
five	O
according	O
to	O
one	O
analysis	O
.	O
</s>
<s>
In	O
mid-1980	O
,	O
the	O
broadly	O
compatible	O
TRS-80	B-Device
Model	O
III	O
was	O
released	O
.	O
</s>
<s>
In	O
April	O
1983	O
,	O
the	O
Model	O
III	O
was	O
succeeded	O
by	O
the	O
compatible	O
TRS-80	B-Device
Model	I-Device
4	I-Device
.	O
</s>
<s>
Following	O
the	O
original	O
Model	O
I	O
and	O
its	O
compatible	O
descendants	O
,	O
the	O
TRS-80	B-Device
name	O
became	O
a	O
generic	O
brand	O
used	O
on	O
other	O
unrelated	O
computer	O
lines	O
sold	O
by	O
Tandy	O
,	O
including	O
the	O
TRS-80	B-Device
Model	I-Device
II	I-Device
,	O
TRS-80	B-Device
Model	I-Device
2000	I-Device
,	O
TRS-80	B-Operating_System
Model	I-Operating_System
100	I-Operating_System
,	O
TRS-80	B-Device
Color	I-Device
Computer	I-Device
,	O
and	O
TRS-80	B-Device
Pocket	I-Device
Computer	I-Device
.	O
</s>
<s>
Among	O
the	O
Tandy	O
employees	O
who	O
purchased	O
a	O
MITS	B-Architecture
Altair	I-Architecture
kit	O
computer	O
was	O
buyer	O
Don	O
French	O
,	O
who	O
began	O
designing	O
his	O
own	O
computer	O
and	O
showed	O
it	O
to	O
vice	O
president	O
of	O
manufacturing	O
John	O
V	O
.	O
Roach	O
,	O
Tandy	O
's	O
former	O
electronic	B-Application
data	I-Application
processing	I-Application
manager	O
.	O
</s>
<s>
Although	O
the	O
design	O
did	O
not	O
impress	O
Roach	O
,	O
the	O
idea	O
of	O
selling	O
a	O
microcomputer	B-Architecture
did	O
.	O
</s>
<s>
When	O
the	O
two	O
men	O
visited	O
National	O
Semiconductor	O
in	O
California	O
in	O
mid-1976	O
,	O
Homebrew	O
Computer	O
Club	O
member	O
Steve	O
Leininger	O
's	O
expertise	O
on	O
the	O
SC/MP	B-Device
microprocessor	O
impressed	O
them	O
.	O
</s>
<s>
Tandy	O
had	O
11	O
million	O
customers	O
that	O
might	O
buy	O
a	O
microcomputer	B-Architecture
,	O
but	O
it	O
would	O
be	O
much	O
more	O
expensive	O
than	O
the	O
median	O
price	O
of	O
a	O
Radio	O
Shack	O
product	O
,	O
and	O
a	O
great	O
risk	O
for	O
the	O
very	O
conservative	O
company	O
.	O
</s>
<s>
As	O
the	O
popularity	O
of	O
CB	B-Application
radio	I-Application
—	O
at	O
one	O
point	O
comprising	O
more	O
than	O
20%	O
of	O
Radio	O
Shack	O
's	O
sales	O
—	O
declined	O
,	O
however	O
,	O
the	O
company	O
sought	O
new	O
products	O
.	O
</s>
<s>
The	O
original	O
retail	O
price	O
required	O
manufacturing	O
cost	O
of	O
;	O
the	O
first	O
design	O
had	O
a	O
membrane	B-Device
keyboard	I-Device
and	O
no	O
video	B-Device
monitor	I-Device
.	O
</s>
<s>
Leininger	O
persuaded	O
Roach	O
and	O
French	O
to	O
include	O
a	O
better	O
keyboard	B-Device
;	O
it	O
,	O
a	O
monitor	O
,	O
datacassette	O
storage	O
,	O
and	O
other	O
features	O
required	O
a	O
higher	O
retail	O
price	O
to	O
provide	O
Tandy	O
's	O
typical	O
profit	O
margin	O
.	O
</s>
<s>
The	O
program	O
quickly	O
crashed	O
as	O
the	O
computer	O
's	O
implementation	O
of	O
Tiny	B-Language
BASIC	I-Language
could	O
not	O
handle	O
the	O
figure	O
that	O
Tandy	O
typed	O
in	O
as	O
his	O
salary	O
,	O
and	O
the	O
two	O
men	O
added	O
support	O
for	O
floating-point	B-Algorithm
math	I-Algorithm
to	O
its	O
Level	B-Language
I	I-Language
BASIC	I-Language
to	O
prevent	O
a	O
recurrence	O
.	O
</s>
<s>
RCA	O
agreed	O
to	O
supply	O
the	O
video	B-Device
monitor	I-Device
—	O
a	O
black-and-white	O
television	O
with	O
the	O
tuner	O
and	O
speakers	O
removed	O
—	O
after	O
others	O
refused	O
because	O
of	O
Tandy	O
's	O
low	O
initial	O
volume	O
of	O
production	O
.	O
</s>
<s>
Tandy	O
used	O
the	O
black-and-silver	O
colors	O
of	O
the	O
RCA	O
CRT	B-Device
unit	O
's	O
cabinet	O
for	O
the	O
TRS-80	B-Device
units	O
also	O
.	O
</s>
<s>
Having	O
spent	O
less	O
than	O
on	O
development	O
,	O
Radio	O
Shack	O
announced	O
the	O
TRS-80	B-Device
(	O
Tandy	O
Radio	O
Shack	O
)	O
at	O
a	O
New	O
York	O
City	O
press	O
conference	O
on	O
August	O
3	O
,	O
1977	O
.	O
</s>
<s>
Six	O
sacks	O
of	O
mail	O
arrived	O
at	O
Tandy	O
headquarters	O
asking	O
about	O
the	O
computer	O
,	O
over	O
15,000	O
people	O
called	O
to	O
purchase	O
a	O
TRS-80	B-Device
—	O
paralyzing	O
the	O
company	O
switchboard	O
—	O
and	O
250,000	O
joined	O
the	O
waiting	O
list	O
with	O
a	O
$100	O
deposit	O
.	O
</s>
<s>
Kornfeld	O
stated	O
when	O
announcing	O
the	O
TRS-80	B-Device
,	O
"	O
This	O
device	O
is	O
inevitably	O
in	O
the	O
future	O
of	O
everyone	O
in	O
the	O
civilized	O
world	O
—	O
in	O
some	O
way	O
—	O
now	O
and	O
so	O
far	O
as	O
ahead	O
as	O
one	O
can	O
think	O
"	O
,	O
and	O
Tandy	O
's	O
1977	O
annual	O
report	O
called	O
the	O
computer	O
"	O
probably	O
the	O
most	O
important	O
product	O
we	O
've	O
ever	O
built	O
in	O
a	O
company	O
factory	O
"	O
.	O
</s>
<s>
Unlike	O
competitor	O
Commodore	O
—	O
which	O
had	O
announced	O
the	O
PET	B-Device
several	O
months	O
earlier	O
but	O
had	O
not	O
yet	O
shipped	O
any	O
—	O
Tandy	O
had	O
its	O
own	O
factories	O
(	O
capable	O
of	O
producing	O
18,000	O
computers	O
a	O
month	O
)	O
and	O
distribution	O
network	O
,	O
and	O
even	O
small	O
towns	O
had	O
Radio	O
Shack	O
stores	O
.	O
</s>
<s>
The	O
company	O
announced	O
plans	O
to	O
be	O
selling	O
by	O
Christmas	O
a	O
range	O
of	O
peripherals	O
and	O
software	O
for	O
the	O
TRS-80	B-Device
,	O
began	O
shipping	O
computers	O
by	O
September	O
,	O
opened	O
its	O
first	O
computer-only	O
store	O
in	O
October	O
,	O
and	O
delivered	O
5,000	O
computers	O
to	O
customers	O
by	O
December	O
.	O
</s>
<s>
Still	O
forecasting	O
3,000	O
sales	O
a	O
year	O
,	O
Radio	O
Shack	O
sold	O
over	O
10,000	O
TRS-80s	B-Device
in	O
its	O
first	O
one	O
and	O
a	O
half	O
months	O
of	O
sales	O
,	O
55,000	O
in	O
its	O
first	O
year	O
,	O
and	O
over	O
200,000	O
during	O
the	O
product	O
's	O
lifetime	O
;	O
one	O
entered	O
the	O
Smithsonian	O
's	O
National	O
Museum	O
of	O
American	O
History	O
.	O
</s>
<s>
By	O
mid-1978	O
the	O
waits	O
of	O
two	O
months	O
or	O
more	O
for	O
delivery	O
were	O
over	O
,	O
and	O
the	O
company	O
could	O
state	O
in	O
advertisements	O
that	O
TRS-80	B-Device
was	O
"	O
on	O
demonstration	O
and	O
available	O
from	O
stock	O
now	O
at	O
every	O
Radio	O
Shack	O
store	O
in	O
this	O
community	O
!	O
"	O
</s>
<s>
The	O
pre-release	O
price	O
for	O
the	O
basic	O
system	O
(	O
CPU/keyboard	O
and	O
video	B-Device
monitor	I-Device
)	O
was	O
and	O
a	O
deposit	O
was	O
required	O
,	O
with	O
a	O
money-back	O
guarantee	O
at	O
time	O
of	O
delivery	O
.	O
</s>
<s>
Kilobaud	O
Microcomputing	B-Architecture
estimated	O
in	O
1980	O
that	O
Tandy	O
was	O
selling	O
three	O
times	O
as	O
many	O
computers	O
as	O
Apple	O
Computer	O
,	O
with	O
both	O
companies	O
ahead	O
of	O
Commodore	O
.	O
</s>
<s>
Hundreds	O
of	O
small	O
companies	O
produced	O
TRS-80	B-Device
software	O
and	O
accessories	O
,	O
and	O
Adam	O
Osborne	O
described	O
Tandy	O
as	O
"	O
the	O
number-one	O
microcomputer	B-Architecture
manufacturer	O
"	O
despite	O
having	O
"	O
so	O
few	O
roots	O
in	O
microcomputing	B-Architecture
"	O
.	O
</s>
<s>
Selling	O
computers	O
did	O
not	O
change	O
the	O
company	O
's	O
"	O
schlocky	O
"	O
image	O
;	O
the	O
Radio	O
Shack	O
name	O
embarrassed	O
business	O
customers	O
,	O
and	O
Tandy	O
executives	O
disliked	O
the	O
"	O
Trash-80	B-Device
"	O
nickname	O
for	O
its	O
products	O
.	O
</s>
<s>
By	O
1979	O
,	O
when	O
Radio	O
Shack	O
launched	O
the	O
business-oriented	O
,	O
and	O
incompatible	O
,	O
TRS-80	B-Device
Model	I-Device
II	I-Device
,	O
the	O
TRS-80	B-Device
was	O
officially	O
renamed	O
the	O
TRS-80	B-Device
Model	I-Device
I	I-Device
to	O
distinguish	O
the	O
two	O
product	O
lines	O
.	O
</s>
<s>
After	O
some	O
exhibitors	O
at	O
the	O
1979	O
Northeast	O
Computer	O
Show	O
were	O
forced	O
to	O
clarify	O
that	O
their	O
products	O
bearing	O
the	O
TRS-80	B-Device
name	O
were	O
not	O
affiliated	O
with	O
Radio	O
Shack	O
,	O
publications	O
and	O
advertisers	O
briefly	O
began	O
to	O
use	O
"	O
S-80	O
"	O
generically	O
rather	O
than	O
"	O
TRS-80	B-Device
"	O
under	O
scare	O
of	O
legal	O
action	O
,	O
though	O
this	O
never	O
materialized	O
.	O
</s>
<s>
The	O
Model	O
I	O
radiated	O
so	O
much	O
interference	O
that	O
,	O
while	O
playing	O
games	B-Application
,	O
an	O
AM	B-Device
radio	O
placed	O
next	O
to	O
the	O
computer	O
could	O
be	O
used	O
to	O
provide	O
sounds	O
.	O
</s>
<s>
Radio	O
Shack	O
offered	O
upgrades	O
(	O
double-density	O
floppy	B-Device
controller	O
,	O
LDOS	B-Operating_System
,	O
memory	O
,	O
reliable	O
keyboard	B-Device
with	O
numeric	B-Algorithm
keypad	O
,	O
lowercase	O
,	O
Level	O
II	O
,	O
RS-232C	O
)	O
as	O
late	O
as	O
1985	O
.	O
</s>
<s>
The	O
Model	O
I	O
combines	O
the	O
mainboard	B-Device
and	O
keyboard	B-Device
into	O
one	O
unit	O
,	O
which	O
became	O
a	O
design	O
trend	O
in	O
the	O
8-bit	O
microcomputer	B-Architecture
era	O
,	O
although	O
the	O
ModelI	O
has	O
a	O
separate	O
power	O
supply	O
unit	O
.	O
</s>
<s>
It	O
uses	O
a	O
Zilog	B-General_Concept
Z80	I-General_Concept
processor	O
clocked	O
at	O
1.78MHz	O
(	O
later	O
models	O
shipped	O
with	O
a	O
Z80A	B-General_Concept
)	O
.	O
</s>
<s>
The	O
OS	B-General_Concept
ROMs	B-Device
,	O
I/O	O
area	O
,	O
video	O
memory	O
and	O
OS	B-General_Concept
work	O
space	O
occupy	O
the	O
first	O
16KB	O
of	O
memory	O
space	O
on	O
the	O
ModelI	O
.	O
</s>
<s>
The	O
remaining	O
48KB	O
of	O
the	O
64KB	O
memory	B-General_Concept
map	I-General_Concept
space	O
is	O
available	O
for	O
program	O
use	O
,	O
subject	O
to	O
the	O
amount	O
of	O
physical	O
RAM	O
installed	O
.	O
</s>
<s>
Although	O
the	O
Z80	B-General_Concept
CPU	B-General_Concept
can	O
use	O
port-based	O
I/O	O
,	O
the	O
ModelI	O
's	O
I/O	O
is	O
memory-mapped	B-Architecture
aside	O
from	O
the	O
cassette	B-Device
tape	I-Device
and	O
RS-232	O
serial	O
ports	O
.	O
</s>
<s>
The	O
TRS-80	B-Device
Model	I-Device
I	I-Device
keyboard	B-Device
uses	O
mechanical	O
switches	O
that	O
suffer	O
from	O
"	O
keyboard	B-Device
bounce	O
"	O
,	O
resulting	O
in	O
multiple	O
letters	O
being	O
typed	O
per	O
keystroke	O
.	O
</s>
<s>
The	O
key	O
switches	O
can	O
be	O
cleaned	O
,	O
but	O
the	O
bounce	O
recurs	O
when	O
the	O
keyboard	B-Device
is	O
reexposed	O
to	O
the	O
contaminating	O
environment	O
.	O
</s>
<s>
Keyboard	B-Device
bounce	O
only	O
occurs	O
in	O
Model	O
I	O
computers	O
with	O
LevelII	O
BASIC	O
firmware	B-Application
;	O
LevelI	O
BASIC	O
has	O
a	O
"	O
debounce	O
"	O
delay	O
to	O
the	O
keyboard	B-Device
driver	O
to	O
avoid	O
the	O
noisy	O
switch	O
contacts	O
.	O
</s>
<s>
Tandy	O
's	O
utility	O
,	O
the	O
ModelIII	O
,	O
the	O
last	O
ModelI	O
firmware	B-Application
,	O
and	O
most	O
third-party	O
operating	B-General_Concept
systems	I-General_Concept
also	O
implement	O
the	O
software	O
fix	O
,	O
and	O
Tandy	O
changed	O
the	O
keyboard	B-Device
during	O
the	O
ModelIII	O
's	O
lifetime	O
to	O
an	O
Alps	O
Electric	O
design	O
with	O
sealed	O
switches	O
.	O
</s>
<s>
The	O
Alps	O
keyboard	B-Device
was	O
available	O
as	O
an	O
upgrade	O
for	O
the	O
ModelI	O
for	O
$79	O
.	O
</s>
<s>
The	O
keyboard	B-Device
is	O
memory-mapped	B-Architecture
so	O
that	O
certain	O
locations	O
in	O
the	O
processor	O
's	O
memory	O
space	O
correspond	O
to	O
the	O
status	O
of	O
a	O
group	O
of	O
keys	O
.	O
</s>
<s>
CPU	B-General_Concept
access	O
to	O
the	O
screen	O
memory	O
causes	O
visible	O
flicker	B-General_Concept
.	O
</s>
<s>
The	O
bus	O
arbitration	O
logic	O
blocks	O
video	O
display	O
refresh	O
(	O
video-RAM	O
reads	O
)	O
during	O
CPU	B-General_Concept
writes	O
to	O
the	O
VRAM	O
,	O
causing	O
a	O
short	O
black	O
line	O
.	O
</s>
<s>
This	O
has	O
little	O
effect	O
on	O
normal	O
BASIC	O
programs	O
,	O
but	O
fast	O
programs	O
made	O
with	O
assembly	B-Language
language	I-Language
can	O
be	O
affected	O
.	O
</s>
<s>
Software	O
authors	O
worked	O
to	O
minimize	O
the	O
effect	O
,	O
and	O
many	O
arcade-style	O
games	B-Application
are	O
available	O
for	O
the	O
Tandy	B-Device
TRS-80	I-Device
.	O
</s>
<s>
Each	O
character	O
is	O
composed	O
of	O
a	O
2×3	O
matrix	O
of	O
pixels	B-Algorithm
,	O
and	O
corresponds	O
to	O
one	O
byte	O
of	O
the	O
1KB	O
video	O
memory	O
used	O
by	O
the	O
TRS-80	B-Device
.	O
</s>
<s>
In	O
each	O
of	O
those	O
bytes	O
,	O
the	O
first	O
six	O
bits	O
control	O
which	O
pixel	B-Algorithm
is	O
displayed	O
.	O
</s>
<s>
The	O
reason	O
that	O
the	O
seventh	O
bit	O
is	O
ignored	O
is	O
due	O
to	O
the	O
company	O
's	O
decision	O
to	O
have	O
only	O
seven	O
2102	O
static-RAM	O
chips	O
installed	O
on	O
the	O
computer	O
's	O
motherboard	B-Device
instead	O
of	O
eight	O
to	O
keep	O
the	O
manufacturing	O
cost	O
low	O
.	O
</s>
<s>
Thus	O
,	O
there	O
are	O
no	O
lowercase	O
letters	O
in	O
the	O
TRS-80	B-Device
character	I-Device
set	I-Device
of	O
an	O
unmodified	O
ModelI	O
,	O
and	O
the	O
number	O
of	O
both	O
graphics	O
symbols	O
and	O
alphanumeric	O
symbols	O
is	O
64	O
.	O
</s>
<s>
The	O
alphanumeric	O
symbols	O
are	O
displayed	O
in	O
5×7	O
matrices	O
of	O
pixels	B-Algorithm
.	O
</s>
<s>
The	O
1978	O
manual	O
for	O
the	O
popular	O
word	O
processor	O
Electric	B-Application
Pencil	I-Application
came	O
with	O
instructions	O
for	O
modifying	O
the	O
computer	O
.	O
</s>
<s>
Most	O
games	B-Application
use	O
this	O
ability	O
for	O
sound	O
effects	O
.	O
</s>
<s>
An	O
adapter	O
was	O
available	O
to	O
use	O
Atari	B-Protocol
joysticks	I-Protocol
.	O
</s>
<s>
User	O
data	O
was	O
originally	O
stored	O
on	O
cassette	B-Device
tape	I-Device
.	O
</s>
<s>
The	O
software-based	O
cassette	B-Device
tape	I-Device
interface	O
is	O
slow	O
and	O
erratic	O
;	O
Green	O
described	O
it	O
as	O
"	O
crummy	O
...	O
drives	O
users	O
up	O
the	O
wall	O
"	O
,	O
and	O
the	O
first	O
issue	O
of	O
80	O
Micro	O
has	O
three	O
articles	O
on	O
how	O
to	O
improve	O
cassette	O
performance	O
.	O
</s>
<s>
To	O
find	O
the	O
correct	O
volume	O
at	O
first	O
use	O
,	O
the	O
load	O
is	O
started	O
and	O
the	O
volume	O
is	O
adjusted	O
until	O
the	O
TRS-80	B-Device
picked	O
up	O
the	O
data	O
.	O
</s>
<s>
Users	O
were	O
instructed	O
to	O
save	O
multiple	O
copies	O
of	O
a	O
software	O
program	O
file	O
,	O
especially	O
if	O
audio	O
tape	B-Device
cassettes	I-Device
instead	O
of	O
certified	O
data	O
tape	O
was	O
used	O
.	O
</s>
<s>
An	O
alternative	O
to	O
using	O
tape	O
was	O
data	O
transmissions	O
from	O
the	O
BBC	O
's	O
Chip	O
Shop	O
programme	O
in	O
the	O
UK	O
,	O
which	O
broadcast	O
software	O
for	O
several	O
different	O
microcomputers	B-Architecture
over	O
the	O
radio	O
.	O
</s>
<s>
Then	O
the	O
radio	O
broadcast	O
was	O
connected	O
to	O
the	O
cassette	B-Device
tape	I-Device
interface	O
.	O
</s>
<s>
TRS-80	B-Device
Model	I-Device
I	I-Device
computers	O
with	O
Level	B-Language
I	I-Language
BASIC	I-Language
read	O
and	O
write	O
tapes	O
at	O
250	O
baud	O
(	O
about	O
30	O
bytes	O
per	O
second	O
)	O
;	O
Level	O
II	O
BASIC	O
doubles	O
this	O
to	O
500	O
baud	O
(	O
about	O
60	O
bytes	O
per	O
second	O
)	O
.	O
</s>
<s>
For	O
loading	O
and	O
storing	O
data	O
from	O
tape	O
,	O
the	O
CPU	B-General_Concept
creates	O
the	O
sound	O
by	O
switching	O
the	O
output	O
voltage	O
between	O
three	O
states	O
,	O
creating	O
crude	O
sine	O
wave	O
audio	O
.	O
</s>
<s>
The	O
ROMs	B-Device
in	O
later	O
models	O
were	O
modified	O
to	O
correct	O
this	O
.	O
</s>
<s>
The	O
TRS-80	B-Device
does	O
not	O
use	O
the	O
S-100	B-Architecture
bus	I-Architecture
like	O
other	O
early	O
8080	O
and	O
Z80-based	O
computers	O
.	O
</s>
<s>
A	O
proprietary	O
Expansion	O
Interface	O
(	O
E/I	O
)	O
box	O
,	O
which	O
fits	O
under	O
the	O
video	B-Device
monitor	I-Device
and	O
served	O
as	O
its	O
base	O
,	O
was	O
offered	O
instead	O
.	O
</s>
<s>
Standard	O
features	O
of	O
the	O
E/I	O
are	O
a	O
floppy	B-Device
disk	I-Device
controller	O
,	O
Centronics	O
parallel	B-Device
port	I-Device
for	O
a	O
printer	O
,	O
and	O
added	O
cassette	O
connector	O
.	O
</s>
<s>
The	O
40-conductor	O
expansion	O
connector	O
passes	O
through	O
to	O
a	O
card	O
edge	O
connector	O
,	O
which	O
permits	O
the	O
addition	O
of	O
external	O
peripherals	O
such	O
as	O
an	O
outboard	O
hard	B-Device
disk	I-Device
drive	I-Device
,	O
a	O
voice	B-Application
synthesizer	I-Application
,	O
or	O
a	O
VOXBOX	O
voice	O
recognition	O
unit	O
.	O
</s>
<s>
The	O
Model	O
I	O
Expansion	O
Interface	O
is	O
the	O
most	O
troublesome	O
part	O
of	O
the	O
TRS-80	B-Device
Model	I-Device
I	I-Device
system	O
.	O
</s>
<s>
The	O
E/I	O
connects	O
to	O
the	O
CPU/keyboard	O
with	O
a	O
6-inch	O
ribbon	O
cable	O
which	O
is	O
unshielded	O
against	O
RF	O
interference	O
and	O
its	O
card	O
edge	O
connector	O
tends	O
to	O
oxidize	O
due	O
to	O
its	O
base	O
metal	O
contacts	O
.	O
</s>
<s>
This	O
demands	O
periodic	O
cleaning	O
with	O
a	O
pencil	O
eraser	O
in	O
order	O
to	O
avoid	O
spontaneous	O
reboots	O
,	O
which	O
contributes	O
to	O
its	O
"	O
Trash-80	B-Device
"	O
sobriquet	O
.	O
</s>
<s>
They	O
accept	O
an	O
"	O
asterisk	O
parameter	O
"	O
,	O
an	O
asterisk	O
(	O
star	O
)	O
character	O
typed	O
following	O
the	O
program	O
name	O
when	O
the	O
program	O
is	O
run	O
from	O
the	O
TRSDOS	B-Operating_System
Ready	O
prompt	O
.	O
</s>
<s>
When	O
used	O
following	O
a	O
spontaneous	O
reboot	O
(	O
or	O
an	O
accidental	O
reset	O
,	O
program	O
crash	O
,	O
or	O
exit	O
to	O
TRSDOS	B-Operating_System
without	O
saving	O
data	O
to	O
disk	O
)	O
,	O
the	O
program	O
loads	O
without	O
initializing	O
its	O
data	O
area(s )	O
,	O
preserving	O
any	O
program	O
data	O
still	O
present	O
from	O
the	O
pre-reboot	O
session	O
.	O
</s>
<s>
Thus	O
,	O
for	O
example	O
,	O
if	O
a	O
VisiCalc	B-Application
user	O
suffers	O
a	O
spontaneous	O
reboot	O
,	O
to	O
recover	O
data	O
the	O
user	O
enters	O
at	O
TRSDOS	B-Operating_System
Ready	O
,	O
and	O
Visicalc	B-Application
restores	O
the	O
previous	O
computing	O
session	O
intact	O
.	O
</s>
<s>
The	O
manuals	O
for	O
the	O
TRS-80	B-Device
advise	O
turning	O
on	O
the	O
monitor	O
first	O
,	O
then	O
any	O
peripherals	O
attached	O
to	O
the	O
E/I	O
(	O
if	O
multiple	O
disk	O
drives	O
are	O
attached	O
,	O
the	O
last	O
drive	O
on	O
the	O
chain	O
is	O
to	O
be	O
powered	O
on	O
first	O
and	O
work	O
down	O
from	O
there	O
)	O
,	O
the	O
E/I	O
,	O
and	O
the	O
computer	O
last	O
.	O
</s>
<s>
This	O
was	O
a	O
common	O
problem	O
on	O
many	O
early	O
floppy	B-Device
drives	I-Device
.	O
</s>
<s>
InfoWorld	O
compared	O
the	O
cable	O
spaghetti	O
connecting	O
the	O
TRS-80	B-Device
Model	I-Device
I	I-Device
's	O
various	O
components	O
to	O
the	O
snakes	O
in	O
Raiders	B-Application
of	I-Application
the	I-Application
Lost	I-Application
Ark	I-Application
.	O
</s>
<s>
Radio	O
Shack	O
offered	O
a	O
"	O
TRS-80	B-Device
System	O
Desk	O
"	O
that	O
concealed	O
nearly	O
all	O
the	O
cabling	O
.	O
</s>
<s>
It	O
can	O
accommodate	O
the	O
complete	O
computer	O
system	O
plus	O
up	O
to	O
four	O
floppy	B-Device
drives	I-Device
and	O
the	O
Quick	O
Printer	O
.	O
</s>
<s>
Also	O
,	O
the	O
friction	O
fit	O
of	O
the	O
edge	O
connector	O
on	O
the	O
already	O
short	O
interconnect	O
cable	O
makes	O
it	O
possible	O
to	O
disconnect	O
the	O
system	O
bus	O
from	O
the	O
CPU	B-General_Concept
if	O
either	O
unit	O
is	O
bumped	O
during	O
operation	O
.	O
</s>
<s>
Radio	O
Shack	O
introduced	O
floppy	B-Device
drives	I-Device
in	O
July	O
1978	O
,	O
about	O
six	O
months	O
after	O
the	O
Model	O
I	O
went	O
on	O
sale	O
.	O
</s>
<s>
The	O
Model	O
I	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
TRSDOS	B-Operating_System
was	O
written	O
by	O
Randy	O
Cook	O
under	O
license	O
from	O
Radio	O
Shack	O
;	O
Randy	O
claimed	O
to	O
have	O
been	O
paid	O
$3000	O
for	O
it	O
.	O
</s>
<s>
Floppy	B-Device
disk	I-Device
operation	O
requires	O
buying	O
the	O
Expansion	O
Interface	O
,	O
which	O
included	O
a	O
single-density	O
floppy	B-Device
disk	I-Device
interface	O
(	O
with	O
a	O
formatted	O
capacity	O
of	O
85K	O
)	O
based	O
on	O
the	O
Western	B-Device
Digital	I-Device
1771	I-Device
single-density	O
floppy	B-Device
disk	I-Device
controller	O
chip	O
.	O
</s>
<s>
Four	O
floppy	B-Device
drives	I-Device
can	O
be	O
daisy-chained	O
to	O
the	O
Model	O
I	O
.	O
</s>
<s>
The	O
early	O
version(s )	O
of	O
TRSDOS	B-Operating_System
are	O
also	O
buggy	O
,	O
and	O
not	O
helped	O
by	O
the	O
Western	B-Device
Digital	I-Device
FD1771	I-Device
chip	O
that	O
cannot	O
reliably	O
report	O
its	O
status	O
for	O
several	O
instruction	O
cycles	O
after	O
it	O
receives	O
a	O
command	O
.	O
</s>
<s>
Early	O
TRSDOS	B-Operating_System
neglects	O
the	O
required	O
yet	O
undocumented	O
wait	O
period	O
,	O
and	O
thus	O
false	O
status	O
often	O
returns	O
to	O
the	O
OS	B-General_Concept
,	O
generating	O
random	O
errors	O
and	O
crashes	O
.	O
</s>
<s>
In	O
1981	O
,	O
Steve	O
Ciarcia	O
published	O
in	O
Byte	O
the	O
design	O
for	O
a	O
homemade	O
,	O
improved	O
expansion	O
interface	O
with	O
more	O
RAM	O
and	O
a	O
disk	O
controller	O
for	O
the	O
TRS-80	B-Device
.	O
</s>
<s>
A	O
data	O
separator	O
and	O
a	O
double-density	O
disk	O
controller	O
(	O
based	O
on	O
the	O
WD	O
1791	O
chip	O
)	O
were	O
made	O
by	O
Percom	B-Device
(	O
a	O
Texas	O
peripheral	O
vendor	O
)	O
,	O
LNW	O
,	O
Tandy	O
,	O
and	O
others	O
.	O
</s>
<s>
The	O
Percom	B-Device
Doubler	O
adds	O
the	O
ability	O
to	O
boot	O
and	O
use	O
double	B-Device
density	I-Device
floppies	B-Device
using	O
a	O
Percom-modified	O
TRSDOS	B-Operating_System
called	O
DoubleDOS	B-Device
.	O
</s>
<s>
The	O
LNDoubler	O
adds	O
the	O
ability	O
to	O
read	O
and	O
write	O
diskette	B-Device
drives	O
with	O
up	O
to	O
720	O
KB	O
of	O
storage	O
,	O
and	O
also	O
the	O
older	O
diskettes	B-Device
with	O
up	O
to	O
1,155	O
KB	O
.	O
</s>
<s>
The	O
combination	O
of	O
40	O
tracks	O
and	O
double	B-Device
density	I-Device
gives	O
a	O
capacity	O
of	O
180	O
kilobytes	O
per	O
single-sided	O
floppy	B-Device
disk	I-Device
.	O
</s>
<s>
Some	O
software	O
publishers	O
formatted	O
one	O
side	O
for	O
Apple	O
systems	O
and	O
the	O
other	O
for	O
the	O
TRS-80	B-Device
.	O
</s>
<s>
The	O
usual	O
method	O
of	O
connecting	O
floppy	B-Device
drives	I-Device
involves	O
setting	O
the	O
drive	O
letter	O
via	O
jumper	O
blocks	O
on	O
the	O
drive	O
controller	O
board	O
,	O
but	O
Tandy	O
opted	O
for	O
a	O
slightly	O
more	O
user-friendly	O
technique	O
where	O
all	O
four	O
select	O
pins	O
on	O
the	O
drives	O
are	O
jumpered	O
and	O
the	O
ribbon	O
cable	O
is	O
missing	O
the	O
Drive	O
Select	O
line	O
.	O
</s>
<s>
A	O
standard	O
flat	O
floppy	B-Device
ribbon	O
cable	O
is	O
usable	O
on	O
the	O
Model	O
I	O
,	O
in	O
which	O
case	O
the	O
drives	O
is	O
jumpered	O
to	O
their	O
number	O
on	O
the	O
chain	O
,	O
or	O
even	O
an	O
IBM	O
PC	O
"	O
twist	O
"	O
cable	O
,	O
which	O
requires	O
setting	O
each	O
drive	O
number	O
to	O
1	O
,	O
but	O
only	O
permits	O
two	O
drives	O
on	O
the	O
chain	O
.	O
</s>
<s>
Although	O
third-party	O
DOSes	O
allow	O
the	O
user	O
to	O
define	O
virtually	O
any	O
floppy	B-Device
format	O
wanted	O
,	O
the	O
"	O
lowest	O
common	O
denominator	O
"	O
format	O
for	O
TRS-80s	B-Device
is	O
the	O
baseline	O
single-density	O
,	O
single-sided	O
,	O
35-40	O
track	O
format	O
of	O
the	O
Model	O
I	O
.	O
</s>
<s>
Third-party	O
vendors	O
like	O
Aerocomp	O
made	O
available	O
double-sided	O
and	O
80	O
track	O
-inch	O
and	O
later	O
-inch	O
floppy	B-Device
drives	I-Device
with	O
up	O
to	O
720	O
KB	O
of	O
storage	O
each	O
.	O
</s>
<s>
An	O
alternative	O
to	O
cassette	B-Device
tape	I-Device
and	O
floppy	B-Device
disk	I-Device
storage	O
from	O
Exatron	O
sold	O
over	O
4,000	O
units	O
by	O
1981	O
.	O
</s>
<s>
The	O
device	O
is	O
a	O
continuous	O
loop	O
tape	O
drive	O
,	O
dubbed	O
the	O
stringy	B-Device
floppy	I-Device
or	O
ESF	O
.	O
</s>
<s>
It	O
requires	O
no	O
Expansion	O
Interface	O
,	O
plugging	O
directly	O
into	O
the	O
TRS-80	B-Device
'	O
s	O
40-pin	O
expansion	O
bus	O
,	O
is	O
much	O
less	O
expensive	O
than	O
a	O
floppy	B-Device
drive	I-Device
,	O
can	O
read	O
and	O
write	O
random-access	O
data	O
like	O
a	O
floppy	B-Device
drive	I-Device
unlike	O
a	O
cassette	B-Device
tape	I-Device
,	O
and	O
it	O
transfers	O
data	O
at	O
up	O
to	O
14,400	O
baud	O
.	O
</s>
<s>
The	O
ESF	O
can	O
coexist	O
with	O
the	O
TRS-80	B-Device
data	O
cassette	O
drive	O
.	O
</s>
<s>
Exatron	O
also	O
made	O
a	O
complementary	O
RAM	O
expansion	O
board	O
that	O
installed	O
in	O
the	O
TRS-80	B-Device
keyboard	B-Device
to	O
increase	O
memory	O
to	O
48	O
KB	O
without	O
the	O
EI	O
.	O
</s>
<s>
Radio	O
Shack	O
introduced	O
a	O
5	O
MB	O
external	O
hard	B-Device
disk	I-Device
for	O
the	O
TRS-80	B-Device
Model	O
III/4	O
in	O
1983	O
.	O
</s>
<s>
It	O
is	O
the	O
same	O
hard	B-Device
disk	I-Device
unit	O
offered	O
for	O
the	O
Model	O
II	O
line	O
,	O
but	O
came	O
with	O
OS	B-General_Concept
software	O
for	O
Model	O
III/4	O
.	O
</s>
<s>
The	O
unit	O
is	O
about	O
the	O
same	O
size	O
as	O
a	O
modern	O
desktop	O
computer	B-General_Concept
enclosure	I-General_Concept
.	O
</s>
<s>
Up	O
to	O
four	O
hard	B-Device
disks	I-Device
can	O
be	O
daisychained	O
for	O
20	O
MB	O
of	O
storage	O
.	O
</s>
<s>
The	O
LDOS	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
by	O
Logical	O
Systems	O
was	O
bundled	O
,	O
which	O
provides	O
utilities	O
for	O
managing	O
the	O
storage	O
space	O
and	O
flexible	O
backup	O
.	O
</s>
<s>
Later	O
,	O
a	O
15MB	O
hard	B-Device
disk	I-Device
was	O
offered	O
in	O
a	O
white	O
case	O
,	O
which	O
can	O
be	O
daisychained	O
for	O
up	O
to	O
60	O
MB	O
.	O
</s>
<s>
Like	O
most	O
hard	B-Device
disks	I-Device
used	O
on	O
8-bit	O
machines	O
,	O
there	O
is	O
no	O
provision	O
for	O
subdirectories	O
,	O
but	O
the	O
DiskDISK	O
utility	O
is	O
a	O
useful	O
alternative	O
that	O
creates	O
virtual	O
hard	B-Device
disk	I-Device
"	O
.DSK	O
"	O
files	O
that	O
can	O
be	O
mounted	O
as	O
another	O
disk	O
drive	O
,	O
and	O
used	O
like	O
a	O
subdirectory	O
would	O
.	O
</s>
<s>
Radio	O
Shack	O
offered	O
an	O
extensive	O
line	O
of	O
printers	O
for	O
the	O
TRS-80	B-Device
family	O
,	O
ranging	O
from	O
basic	O
9-pin	O
dot	O
matrix	O
units	O
to	O
large	O
wide-carriage	O
line	O
printers	O
for	O
professional	O
use	O
,	O
daisy-wheel	O
printers	O
,	O
ink	O
jet	O
printers	O
,	O
laser	O
printers	O
and	O
color	O
plotters	B-Operating_System
.	O
</s>
<s>
All	O
have	O
a	O
Centronics-standard	O
interface	O
and	O
after	O
the	O
introduction	O
of	O
the	O
Color	B-Device
Computer	I-Device
in	O
1980	O
,	O
many	O
also	O
had	O
a	O
connector	O
for	O
the	O
CoCo	O
's	O
serial	O
interface	O
.	O
</s>
<s>
FP-215	O
is	O
a	O
flatbed	O
plotter	B-Operating_System
.	O
</s>
<s>
Level	B-Language
I	I-Language
BASIC	I-Language
fits	O
in	O
4	O
KB	O
of	O
ROM	B-Device
,	O
and	O
Level	O
II	O
BASIC	O
fits	O
into	O
12	O
KB	O
of	O
ROM	B-Device
.	O
</s>
<s>
Level	O
II	O
introduced	O
double	O
precision	O
floating	B-Algorithm
point	I-Algorithm
support	O
and	O
has	O
a	O
much	O
wider	O
set	O
of	O
commands	O
.	O
</s>
<s>
Level	B-Language
I	I-Language
BASIC	I-Language
is	O
based	O
on	O
Li-Chen	O
Wang	O
's	O
free	O
Tiny	B-Language
BASIC	I-Language
with	O
more	O
functions	O
added	O
by	O
Radio	O
Shack	O
.	O
</s>
<s>
Level	B-Language
I	I-Language
BASIC	I-Language
has	O
only	O
two	O
string	O
variables	O
(	O
A$	O
and	O
B$	O
)	O
,	O
26	O
numeric	B-Algorithm
variables	O
(	O
A	O
–	O
Z	O
)	O
,	O
and	O
one	O
array	O
,	O
A( )	O
.	O
</s>
<s>
Code	O
for	O
functions	O
like	O
SIN( )	O
,	O
COS( )	O
and	O
TAN( )	O
is	O
not	O
included	O
in	O
ROM	B-Device
but	O
printed	O
at	O
the	O
end	O
of	O
the	O
book	O
.	O
</s>
<s>
for	O
arithmetic	O
errors	O
such	O
as	O
division	B-Algorithm
by	I-Algorithm
zero	I-Algorithm
,	O
and	O
"	O
SORRY	O
"	O
for	O
out	B-General_Concept
of	I-General_Concept
memory	I-General_Concept
errors	O
.	O
</s>
<s>
Level	B-Language
I	I-Language
BASIC	I-Language
is	O
not	O
tokenized	O
;	O
reserved	O
words	O
are	O
stored	O
literally	O
.	O
</s>
<s>
Radio	O
Shack	O
always	O
intended	O
for	O
Level	B-Language
I	I-Language
BASIC	I-Language
to	O
be	O
a	O
stopgap	O
until	O
Level	O
II	O
was	O
ready	O
,	O
and	O
the	O
first	O
brochure	O
for	O
the	O
Model	O
I	O
in	O
January	O
1978	O
mentioned	O
that	O
Level	O
II	O
BASIC	O
was	O
"	O
coming	O
soon	O
"	O
.	O
</s>
<s>
It	O
is	O
an	O
abridged	O
version	O
of	O
the	O
16K	O
Extended	B-Language
BASIC	I-Language
,	O
since	O
the	O
Model	O
I	O
has	O
12	O
KB	O
of	O
ROM	B-Device
space	O
.	O
</s>
<s>
According	O
to	O
Bill	O
Gates	O
,	O
"	O
It	O
was	O
a	O
sort	O
of	O
intermediate	O
between	O
8K	O
BASIC	O
and	O
Extended	B-Language
BASIC	I-Language
.	O
</s>
<s>
Some	O
features	O
from	O
Extended	B-Language
BASIC	I-Language
such	O
as	O
descriptive	O
errors	O
and	O
user	O
defined	O
functions	O
were	O
not	O
included	O
,	O
but	O
there	O
were	O
double	O
precision	O
variables	O
and	O
the	O
PRINT	O
USING	O
statement	O
that	O
we	O
wanted	O
to	O
get	O
in	O
.	O
</s>
<s>
Original	O
Level	O
I	O
BASIC-equipped	O
machines	O
could	O
be	O
retrofitted	O
to	O
Level	O
II	O
through	O
a	O
ROM	B-Device
replacement	O
performed	O
by	O
Radio	O
Shack	O
for	O
a	O
fee	O
(	O
originally	O
$199	O
)	O
.	O
</s>
<s>
Users	O
with	O
Level	B-Language
I	I-Language
BASIC	I-Language
programs	O
stored	O
on	O
cassette	O
have	O
to	O
convert	O
these	O
to	O
the	O
tokenized	O
Level	O
II	O
BASIC	O
before	O
use	O
.	O
</s>
<s>
A	O
utility	O
for	O
this	O
was	O
provided	O
with	O
the	O
Level	O
II	O
ROMS	B-Device
.	O
</s>
<s>
Disk	O
BASIC	O
allows	O
disk	O
I/O	O
,	O
and	O
in	O
some	O
cases	O
(	O
NewDos/80	B-Operating_System
,	O
MultiDOS	O
,	O
DosPlus	B-Operating_System
,	O
LDOS	B-Operating_System
)	O
adds	O
powerful	O
sorting	O
,	O
searching	O
,	O
full	O
screen	O
editing	O
,	O
and	O
other	O
features	O
.	O
</s>
<s>
Level	O
II	O
BASIC	O
reserves	O
some	O
of	O
these	O
keywords	O
and	O
issues	O
a	O
"	O
?	O
L3	O
ERROR	O
"	O
,	O
suggesting	O
a	O
behind-the-scenes	O
change	O
of	O
direction	O
intervened	O
between	O
the	O
creation	O
of	O
the	O
Level	O
II	O
ROMs	B-Device
and	O
the	O
introduction	O
of	O
Disk	O
BASIC	O
.	O
</s>
<s>
Microsoft	O
also	O
marketed	O
an	O
enhanced	O
BASIC	O
called	O
Level	O
III	O
BASIC	O
written	O
by	O
Bill	O
Gates	O
,	O
on	O
cassette	B-Device
tape	I-Device
.	O
</s>
<s>
Level	O
III	O
BASIC	O
adds	O
most	O
of	O
the	O
functions	O
in	O
the	O
full	O
16	O
KB	O
version	O
of	O
BASIC	O
plus	O
many	O
other	O
TRS-80	B-Device
specific	O
enhancements	O
.	O
</s>
<s>
Many	O
of	O
Level	O
III	O
BASIC	O
's	O
features	O
are	O
included	O
in	O
the	O
TRS-80	B-Device
Model	O
III	O
's	O
Level	O
II	O
BASIC	O
and	O
disk	O
BASIC	O
.	O
</s>
<s>
Level	B-Language
I	I-Language
BASIC	I-Language
was	O
still	O
offered	O
on	O
the	O
Model	O
I	O
in	O
either	O
4K	O
or	O
16K	O
configurations	O
after	O
the	O
introduction	O
of	O
Level	O
II	O
BASIC	O
.	O
</s>
<s>
Radio	O
Shack	O
published	O
a	O
combined	O
assembler	B-Language
and	O
program	O
editing	O
package	O
called	O
the	O
Series	O
I	O
Assembler	B-Language
Editor	O
.	O
</s>
<s>
80	O
Micro	O
magazine	O
printed	O
a	O
modification	O
enabling	O
it	O
to	O
run	O
under	O
the	O
Model	B-Device
4	I-Device
's	O
TRSDOS	B-Operating_System
Version	O
6	O
.	O
</s>
<s>
Microsoft	O
made	O
its	O
Fortran	B-Application
,	O
COBOL	B-Application
and	O
BASCOM	O
BASIC	O
compiler	O
available	O
through	O
Radio	O
Shack	O
.	O
</s>
<s>
In	O
1982	O
,	O
Scientific	O
Time	O
Sharing	O
Corporation	O
published	O
a	O
version	O
of	O
its	O
APL	B-Language
for	O
the	O
TRS-80	B-Device
Model	O
III	O
as	O
APL*	O
PLUS/80	O
.	O
</s>
<s>
Blackjack	B-Application
and	O
backgammon	B-Application
came	O
with	O
the	O
TRS-80	B-Device
,	O
and	O
at	O
its	O
debut	O
Radio	O
Shack	O
offered	O
four	O
payroll	O
,	O
personal	O
finance	O
,	O
and	O
educational	O
programs	O
on	O
cassette	O
.	O
</s>
<s>
They	O
do	O
n't	O
want	O
the	O
TRS-80	B-Device
buyers	O
to	O
know	O
that	O
there	O
is	O
anything	O
more	O
than	O
their	O
handful	O
of	O
mediocre	O
programs	O
available	O
"	O
,	O
many	O
of	O
which	O
"	O
are	O
disastrous	O
and	O
,	O
I	O
'm	O
sure	O
,	O
doing	O
tremendous	O
damage	O
to	O
the	O
industry	O
"	O
.	O
</s>
<s>
Broderbund	O
,	O
founded	O
that	O
year	O
,	O
began	O
by	O
publishing	O
TRS-80	B-Device
software	O
,	O
but	O
by	O
1983	O
cofounder	O
Doug	O
Carlston	O
said	O
that	O
the	O
computer	O
"	O
turned	O
out	O
to	O
be	O
a	O
terrible	O
market	O
because	O
most	O
of	O
the	O
distribution	O
networks	O
were	O
closed	O
,	O
even	O
though	O
there	O
were	O
plenty	O
of	O
machines	O
out	O
there	O
"	O
.	O
</s>
<s>
An	O
author	O
wrote	O
in	O
a	O
1979	O
article	O
on	O
the	O
computer	O
's	O
"	O
mystery	O
of	O
machine	O
language	O
graphics	O
control	O
"	O
that	O
"	O
Radio	O
Shack	O
seems	O
to	O
hide	O
the	O
neat	O
little	O
jewels	O
of	O
information	O
a	O
hobbyist	O
needs	O
to	O
make	O
a	O
treasure	O
of	O
the	O
TRS-80	B-Device
"	O
.	O
</s>
<s>
He	O
stated	O
that	O
other	O
than	O
the	O
"	O
excellent	O
"	O
Level	B-Language
I	I-Language
BASIC	I-Language
manual	O
"	O
there	O
has	O
been	O
little	O
information	O
until	O
recently	O
...	O
TRS-80	B-Device
owners	O
must	O
be	O
resourceful	O
"	O
,	O
reporting	O
that	O
the	O
computer	O
's	O
"	O
keyboard	B-Device
,	O
video	O
,	O
and	O
cassette	O
"	O
functionality	O
were	O
also	O
undocumented	O
.	O
</s>
<s>
The	O
first	O
book	O
authorized	O
by	O
Tandy	O
with	O
technical	O
information	O
on	O
TRSDOS	B-Operating_System
for	O
the	O
Model	O
I	O
did	O
not	O
appear	O
until	O
after	O
the	O
computer	O
's	O
discontinuation	O
.	O
</s>
<s>
By	O
1982	O
,	O
the	O
company	O
admitted	O
—	O
after	O
no	O
software	O
appeared	O
for	O
the	O
Model	O
16	O
after	O
five	O
months	O
—	O
that	O
it	O
should	O
have	O
,	O
like	O
Apple	O
,	O
encouraged	O
third-party	O
developers	O
of	O
products	O
like	O
the	O
killer	O
app	O
VisiCalc	B-Application
.	O
</s>
<s>
(	O
A	O
lengthy	O
1980	O
article	O
in	O
a	O
Tandy	O
publication	O
introducing	O
the	O
TRS-80	B-Device
version	O
of	O
VisiCalc	B-Application
did	O
not	O
mention	O
that	O
the	O
spreadsheet	O
had	O
been	O
available	O
for	O
the	O
Apple	B-Device
II	I-Device
for	O
a	O
year	O
.	O
)	O
</s>
<s>
However	O
,	O
in	O
the	O
early	O
1980s	O
,	O
it	O
was	O
not	O
uncommon	O
for	O
small	O
companies	O
and	O
municipalities	O
to	O
write	O
custom	O
programs	O
for	O
computers	O
such	O
as	O
the	O
TRS-80	B-Device
to	O
process	O
a	O
variety	O
of	O
data	O
.	O
</s>
<s>
In	O
one	O
case	O
a	O
small	O
town	O
's	O
vehicle	O
fleet	O
was	O
managed	O
from	O
a	O
single	O
TRS-80	B-Device
.	O
</s>
<s>
By	O
1985	O
,	O
the	O
company	O
's	O
Ed	O
Juge	O
stated	O
that	O
other	O
than	O
Scripsit	B-Protocol
and	O
DeskMate	B-Device
,	O
"	O
we	O
intend	O
to	O
rely	O
mostly	O
on	O
'	O
big-name	O
'	O
,	O
market	O
proven	O
software	O
from	O
leading	O
software	O
firms	O
"	O
.	O
</s>
<s>
A	O
full	O
suite	O
of	O
office	O
applications	O
became	O
available	O
from	O
the	O
company	O
and	O
others	O
,	O
including	O
the	O
VisiCalc	B-Application
and	O
Multiplan	B-Device
spreadsheets	O
and	O
the	O
Lazy	O
Writer	O
,	O
Electric	B-Application
Pencil	I-Application
,	O
and	O
from	O
Radio	O
Shack	O
itself	O
the	O
Scripsit	B-Protocol
and	O
SuperScripsit	O
word	O
processors	O
.	O
</s>
<s>
Compared	O
to	O
the	O
contemporary	O
Commodore	O
and	O
Apple	O
micros	O
,	O
the	O
TRS-80	B-Device
'	O
s	O
block	O
graphics	O
and	O
crude	O
sound	O
were	O
widely	O
considered	O
limited	O
.	O
</s>
<s>
TRS-80	B-Device
arcade	O
games	B-Application
tended	O
to	O
be	O
faster	O
with	O
effects	O
that	O
emphasized	O
motion	O
.	O
</s>
<s>
This	O
perceived	O
disadvantage	O
did	O
not	O
deter	O
independent	O
software	O
companies	O
such	O
as	O
Big	B-Device
Five	I-Device
Software	I-Device
from	O
producing	O
unlicensed	O
versions	O
of	O
arcade	O
games	B-Application
like	O
Namco	O
's	O
Galaxian	B-Application
,	O
Atari	O
's	O
Asteroids	B-Application
,	O
Taito	O
's	O
Lunar	B-Application
Rescue	I-Application
,	O
Williams	O
's	O
Make	B-Application
Trax	I-Application
,	O
and	O
Exidy	O
's	O
Targ	B-Application
and	O
Venture	B-Application
.	O
</s>
<s>
Sega	O
's	O
Frogger	B-Application
and	O
Zaxxon	B-Application
were	O
ported	O
to	O
the	O
computer	O
and	O
marketed	O
by	O
Radio	O
Shack	O
.	O
</s>
<s>
Namco/Midway	O
'	O
s	O
Pac-Man	B-Application
was	O
cloned	O
by	O
Philip	O
Oliver	O
and	O
distributed	O
by	O
Cornsoft	O
Group	O
as	O
Scarfman	B-Application
.	O
</s>
<s>
Atari	O
's	O
Battlezone	B-Application
was	O
cloned	O
for	O
the	O
Models	O
I/III	O
by	O
Wayne	O
Westmoreland	O
and	O
Terry	O
Gilman	O
and	O
published	O
by	O
Adventure	O
International	O
as	O
Armored	O
Patrol	O
.	O
</s>
<s>
They	O
also	O
cloned	O
Eliminator	O
(	O
based	O
on	O
Defender	B-Application
)	O
and	O
Donkey	B-Application
Kong	I-Application
;	O
the	O
latter	O
was	O
n't	O
published	O
until	O
after	O
the	O
TRS-80	B-Device
was	O
discontinued	O
,	O
because	O
Nintendo	O
refused	O
to	O
license	O
the	O
game	O
.	O
</s>
<s>
Some	O
games	B-Application
originally	O
written	O
for	O
other	O
computers	O
were	O
ported	O
to	O
the	O
TRS-80	B-Device
.	O
</s>
<s>
Microchess	B-Application
has	O
three	O
levels	O
of	O
play	O
and	O
can	O
run	O
in	O
the	O
4	O
KB	O
of	O
memory	O
that	O
is	O
standard	O
with	O
the	O
ModelI	O
;	O
the	O
classic	O
ELIZA	B-Application
is	O
another	O
TRS-80	B-Device
port	O
.	O
</s>
<s>
Apple	B-Application
Panic	I-Application
,	O
itself	O
a	O
clone	O
of	O
Universal	O
's	O
Space	B-Application
Panic	I-Application
,	O
was	O
written	O
for	O
the	O
TRS-80	B-Device
by	O
Yves	O
Lempereur	O
and	O
published	O
by	O
Funsoft	O
.	O
</s>
<s>
Epyxs	O
Temple	B-Application
of	I-Application
Apshai	I-Application
runs	O
slowly	O
on	O
the	O
TRS-80	B-Device
.	O
</s>
<s>
Infocom	O
ported	O
its	O
series	O
of	O
interactive	O
text-based	O
adventure	O
games	B-Application
to	O
the	O
Models	O
I/III	O
;	O
the	O
first	O
,	O
Zork	B-Application
I	I-Application
,	O
was	O
marketed	O
by	O
Radio	O
Shack	O
.	O
</s>
<s>
Adventure	O
International	O
's	O
text	O
adventures	O
began	O
on	O
the	O
TRS-80	B-Device
,	O
as	O
did	O
Sea	B-Application
Dragon	I-Application
by	O
Westmoreland	O
and	O
Gilman	O
,	O
later	O
ported	O
to	O
the	O
other	O
home	O
micros	O
.	O
</s>
<s>
Android	B-Application
Nim	I-Application
by	O
Leo	O
Christopherson	O
was	O
rewritten	O
for	O
the	O
Commodore	B-Device
PET	I-Device
and	O
Apple	O
.	O
</s>
<s>
Many	O
games	B-Application
are	O
unique	O
to	O
the	O
TRS-80	B-Device
,	O
including	O
Duel-N-Droids	O
,	O
also	O
by	O
Christopherson	O
,	O
an	O
early	O
first-person	O
shooter	O
13	O
Ghosts	O
by	O
Software	O
Affair	O
(	O
the	O
Orchestra-80	O
,	O
-85	O
and	O
-90	O
people	O
)	O
and	O
shooters	O
like	O
Cosmic	O
Fighter	O
and	O
Defence	O
Command	O
,	O
and	O
strange	O
experimental	O
programs	O
such	O
as	O
Christopherson	O
's	O
Dancing	O
Demon	O
,	O
in	O
which	O
the	O
player	O
composes	O
a	O
song	O
for	O
a	O
devil	O
and	O
choreographs	O
his	O
dance	O
steps	O
to	O
the	O
music	O
.	O
</s>
<s>
Other	O
utility	O
software	O
such	O
as	O
Stewart	O
Software	O
's	O
Toolkit	O
offered	O
the	O
first	O
sorted	O
directory	O
,	O
decoding	O
or	O
reset	O
of	O
passwords	O
,	O
and	O
the	O
ability	O
to	O
eliminate	O
parts	O
of	O
TRSDOS	B-Operating_System
that	O
were	O
not	O
needed	O
in	O
order	O
to	O
free	O
up	O
floppy	B-Device
disk	I-Device
space	O
.	O
</s>
<s>
They	O
also	O
produced	O
the	O
On-Line	O
80	O
BBS	O
,	O
a	O
TRSDOS	B-Operating_System
based	O
Bulletin	O
Board	O
System	O
.	O
</s>
<s>
Misosys	O
Inc	O
.	O
was	O
a	O
prolific	O
producer	O
of	O
sophisticated	O
TRS-80	B-Device
utility	O
and	O
language	O
software	O
for	O
all	O
models	O
of	O
TRS-80	B-Device
from	O
the	O
very	O
beginning	O
.	O
</s>
<s>
Perhaps	O
because	O
of	O
the	O
lack	O
of	O
information	O
on	O
TRSDOS	B-Operating_System
and	O
its	O
bugs	O
,	O
by	O
1982	O
perhaps	O
more	O
operating	B-General_Concept
systems	I-General_Concept
existed	O
for	O
the	O
TRS-80	B-Device
than	O
for	O
any	O
other	O
computer	O
.	O
</s>
<s>
TRSDOS	B-Operating_System
is	O
limited	O
in	O
its	O
capabilities	O
,	O
since	O
like	O
Apple	O
DOS	O
3.3	O
on	O
the	O
Apple	B-Device
II	I-Device
,	O
it	O
is	O
mainly	O
conceived	O
of	O
as	O
a	O
way	O
of	O
extending	O
BASIC	O
to	O
support	O
disk	O
drives	O
.	O
</s>
<s>
Numerous	O
alternative	O
DOSes	O
appeared	O
,	O
the	O
most	O
prominent	O
being	O
LDOS	B-Operating_System
because	O
Radio	O
Shack	O
licensed	O
it	O
from	O
Logical	O
Systems	O
and	O
adopted	O
it	O
as	O
its	O
official	O
DOS	O
for	O
its	O
Models	O
I	O
and	O
III	O
hard	B-Device
disk	I-Device
drive	I-Device
products	O
.	O
</s>
<s>
Other	O
alternative	O
TRS-80	B-Device
DOSes	O
included	O
NewDOS	B-Operating_System
from	O
Apparat	O
Personal	O
Computers	O
,	O
and	O
DoubleDOS	B-Device
,	O
DOSPlus	B-Operating_System
,	O
MicroDOS	B-Operating_System
,	O
UltraDOS	O
(	O
later	O
called	O
Multidos	O
)	O
.	O
</s>
<s>
The	O
DOS	O
for	O
the	O
Model	B-Device
4	I-Device
line	O
was	O
originally	O
called	O
TRSDOS	B-Operating_System
Version	O
6	O
but	O
was	O
actually	O
produced	O
by	O
and	O
licensed	O
from	O
Logical	O
Systems	O
,	O
and	O
is	O
technically	O
a	O
descendant	O
of	O
the	O
original	O
Model	O
I	O
LDOS	B-Operating_System
.	O
</s>
<s>
The	O
memory	B-General_Concept
map	I-General_Concept
of	O
the	O
Model	O
I	O
and	O
III	O
render	O
them	O
incompatible	O
with	O
the	O
standard	O
CP/M	B-Application
OS	B-General_Concept
for	O
Z80	B-General_Concept
business	O
computers	O
,	O
which	O
loads	O
at	O
hexadecimal	O
address	O
$0000	O
with	O
TPA	O
(	O
Transient	O
Program	O
Area	O
)	O
starting	O
at	O
$0100	O
;	O
the	O
TRS-80	B-Device
ROM	B-Device
resides	O
in	O
this	O
address	O
space	O
.	O
</s>
<s>
Omikron	O
Systems	O
 '	O
Mappers	O
board	O
remaps	O
the	O
ROM	B-Device
to	O
run	O
unmodified	O
CP/M	B-Application
programs	O
on	O
the	O
Model	O
I	O
.	O
</s>
<s>
A	O
customized	O
version	O
of	O
CP/M	B-Application
is	O
available	O
,	O
but	O
loses	O
its	O
portability	O
advantage	O
.	O
</s>
<s>
80	O
Micro	O
magazine	O
published	O
a	O
do-it-yourself	O
CP/M	B-Application
modification	O
for	O
the	O
Model	O
III	O
.	O
</s>
<s>
Dan	O
Fylstra	O
,	O
among	O
the	O
first	O
owners	O
,	O
wrote	O
in	O
Byte	O
in	O
April	O
1978	O
that	O
as	O
an	O
"	O
 '	O
appliance	O
 '	O
computer	O
...	O
the	O
TRS-80	B-Device
brings	O
the	O
personal	O
computer	O
a	O
good	O
deal	O
closer	O
to	O
the	O
average	O
customer	O
"	O
,	O
suitable	O
for	O
home	O
and	O
light	O
business	O
use	O
.	O
</s>
<s>
Jerry	O
Pournelle	O
wrote	O
in	O
1980	O
that	O
"	O
the	O
basic	O
TRS-80	B-Device
is	O
a	O
lot	O
of	O
computer	O
for	O
the	O
money	O
"	O
.	O
</s>
<s>
Pournelle	O
reported	O
,	O
however	O
,	O
that	O
with	O
the	O
Omikron	O
board	O
,	O
a	O
customer	O
paid	O
less	O
than	O
$5000	O
for	O
a	O
computer	O
compatible	O
with	O
TRS-80	B-Device
and	O
CP/M	B-Application
software	O
"	O
all	O
without	O
building	O
a	O
single	O
kit	O
"	O
.	O
</s>
<s>
He	O
wrote	O
in	O
May	O
1983	O
,	O
"	O
As	O
to	O
our	O
TRS-80	B-Device
Model	I-Device
I	I-Device
,	O
we	O
trashed	O
that	O
sucker	O
long	O
ago	O
.	O
</s>
<s>
(	O
The	O
TRS-80	B-Device
Model	I-Device
II	I-Device
is	O
an	O
entirely	O
different	O
and	O
incompatible	O
design	O
)	O
.	O
</s>
<s>
Tandy	O
released	O
the	O
TRS-80	B-Device
Model	O
III	O
on	O
July	O
26	O
,	O
1980	O
.	O
</s>
<s>
The	O
improvements	O
of	O
the	O
Model	O
III	O
over	O
the	O
Model	O
I	O
include	O
:	O
built-in	O
lowercase	O
,	O
a	O
better	O
keyboard	B-Device
with	O
repeating	O
keys	O
,	O
an	O
enhanced	O
character	O
set	O
,	O
a	O
real-time	O
clock	O
,	O
1500-baud	O
cassette	O
interface	O
,	O
a	O
faster	O
(	O
2.03MHz	O
)	O
Z80	B-General_Concept
processor	O
,	O
and	O
an	O
all-in-one	O
enclosure	O
requiring	O
fewer	O
cables	O
.	O
</s>
<s>
A	O
Model	O
III	O
with	O
two	O
floppy	B-Device
drives	I-Device
requires	O
the	O
use	O
of	O
only	O
one	O
electrical	O
outlet	O
;	O
a	O
two-drive	O
Model	O
I	O
requires	O
five	O
outlets	O
.	O
</s>
<s>
Tandy	O
distinguished	O
between	O
the	O
high-end	O
Model	O
II	O
and	O
Model	O
III	O
,	O
describing	O
the	O
former	O
as	O
"	O
an	O
administrative	O
system	O
,	O
good	O
for	O
things	O
like	O
word	O
processing	O
,	O
data	O
management	O
and	O
VisiCalc	B-Application
operations	O
"	O
and	O
suitable	O
for	O
small	O
businesses	O
.	O
</s>
<s>
The	O
computer	O
's	O
CPU	B-General_Concept
board	O
has	O
three	O
banks	O
of	O
sockets	O
(	O
8	O
sockets	O
to	O
a	O
bank	O
)	O
which	O
take	O
type	O
4116	O
DRAMs	O
,	O
so	O
memory	O
configurations	O
come	O
in	O
16	O
KB	O
,	O
32	O
KB	O
,	O
or	O
48	O
KB	O
RAM	O
memory	O
sizes	O
.	O
</s>
<s>
Computers	O
with	O
32	O
KB	O
or	O
48	O
KB	O
RAM	O
can	O
be	O
upgraded	O
with	O
floppy	B-Device
disk	I-Device
drive	I-Device
storage	O
.	O
</s>
<s>
Third-party	O
suppliers	O
offered	O
double-sided	O
and	O
80-track	O
drives	O
,	O
though	O
to	O
control	O
them	O
they	O
had	O
to	O
modify	O
the	O
TRSDOS	B-Operating_System
driver	O
code	O
or	O
else	O
furnish	O
an	O
alternative	O
third-party	O
DOS	O
which	O
could	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
The	O
installation	O
of	O
floppy	B-Device
disk	I-Device
drives	I-Device
also	O
requires	O
the	O
computer	O
's	O
power	O
supply	O
to	O
be	O
upgraded	O
.	O
</s>
<s>
There	O
is	O
no	O
internal	O
cooling	O
fan	O
in	O
the	O
Model	O
III	O
;	O
it	O
uses	O
passive	O
convection	O
cooling	O
(	O
unless	O
an	O
unusual	O
number	O
of	O
power-hungry	O
expansions	O
were	O
installed	O
internally	O
,	O
such	O
as	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
,	O
graphics	O
board	O
,	O
speedup	O
kit	O
,	O
RS-232	O
board	O
,	O
etc	O
.	O
</s>
<s>
The	O
Model	O
III	O
's	O
memory	B-General_Concept
map	I-General_Concept
and	O
system	O
architecture	O
is	O
mostly	O
the	O
same	O
as	O
the	O
Model	O
I	O
,	O
but	O
the	O
disk	O
drives	O
and	O
printer	B-Device
port	I-Device
were	O
moved	O
from	O
memory	B-General_Concept
mapped	I-General_Concept
to	O
port	B-Architecture
I/O	I-Architecture
,	O
thus	O
Model	O
I	O
software	O
that	O
attempts	O
to	O
manipulate	O
the	O
disk	O
controller	O
directly	O
or	O
output	O
to	O
the	O
printer	O
(	O
in	O
particular	O
Model	O
I	O
DOSes	O
and	O
application	O
packages	O
such	O
as	O
Visicalc	B-Application
and	O
Scripsit	B-Protocol
)	O
will	O
not	O
work	O
.	O
</s>
<s>
Under	O
the	O
supplied	O
TRSDOS	B-Operating_System
1.3	O
operating	B-General_Concept
system	I-General_Concept
Model	O
I	O
disks	O
can	O
be	O
read	O
in	O
the	O
Model	O
III	O
,	O
but	O
not	O
vice	O
versa	O
.	O
</s>
<s>
The	O
optional	O
LDOS	B-Operating_System
OS	B-General_Concept
(	O
by	O
Logical	O
Systems	O
Inc	O
.	O
)	O
use	O
a	O
common	O
disk	O
format	O
for	O
both	O
Model	O
I	O
and	O
Model	O
III	O
versions	O
.	O
</s>
<s>
Customers	O
and	O
developers	O
complained	O
of	O
bugs	O
in	O
the	O
Model	O
III	O
's	O
Microsoft	B-Language
BASIC	I-Language
interpreter	B-Application
and	O
TRSDOS	B-Operating_System
.	O
</s>
<s>
Tandy/Radio	O
Shack	O
(	O
and	O
TRS-80	B-Device
magazines	O
like	O
80	O
Micro	O
)	O
periodically	O
published	O
many	O
software	O
patches	O
to	O
correct	O
these	O
deficiencies	O
and	O
to	O
permit	O
users	O
to	O
customize	O
the	O
software	O
to	O
their	O
preferences	O
.	O
</s>
<s>
Differences	O
in	O
the	O
WD1771	B-Device
and	O
WD1791	O
floppy	B-Device
controllers	O
created	O
problems	O
reading	O
Model	O
I	O
disks	O
on	O
a	O
Model	O
III	O
(	O
the	O
double-density	O
upgrade	O
in	O
the	O
Model	O
I	O
include	O
both	O
chips	O
while	O
a	O
Model	O
III	O
had	O
only	O
the	O
WD1791	O
)	O
.	O
</s>
<s>
The	O
WD1771	B-Device
supports	O
four	O
data	O
markers	O
while	O
the	O
WD1791	O
only	O
supports	O
two	O
,	O
and	O
some	O
versions	O
of	O
TRSDOS	B-Operating_System
for	O
the	O
Model	O
I	O
also	O
use	O
them	O
.	O
</s>
<s>
The	O
WD1791	O
supports	O
the	O
500	O
bit/s	O
bitrate	O
needed	O
for	O
high-density	O
floppy	B-Device
drives	I-Device
,	O
but	O
the	O
controller	O
is	O
not	O
capable	O
of	O
using	O
them	O
without	O
extensive	O
modifications	O
.	O
</s>
<s>
TRSDOS	B-Operating_System
for	O
the	O
Model	O
III	O
was	O
developed	O
in-house	O
by	O
Radio	O
Shack	O
rather	O
than	O
being	O
contracted	O
out	O
like	O
the	O
Model	O
I	O
's	O
DOS	O
.	O
</s>
<s>
Two	O
early	O
versions	O
,	O
1.1	O
and	O
1.2	O
,	O
were	O
replaced	O
by	O
version	O
1.3	O
in	O
1981	O
which	O
became	O
the	O
standard	O
Model	O
III	O
OS	B-General_Concept
.	O
</s>
<s>
TRSDOS	B-Operating_System
1.3	O
is	O
not	O
format	O
compatible	O
with	O
1.1	O
and	O
1.2	O
;	O
a	O
utility	O
called	O
XFERSYS	O
is	O
provided	O
which	O
converted	O
older	O
format	O
disks	O
to	O
TRSDOS	B-Operating_System
1.3	O
format	O
(	O
this	O
change	O
is	O
permanent	O
and	O
the	O
resultant	O
disks	O
cannot	O
be	O
read	O
with	O
the	O
older	O
DOS	O
versions	O
)	O
.	O
</s>
<s>
Instead	O
of	O
displaying	O
garbage	O
on	O
screen	O
at	O
power	O
up	O
,	O
it	O
displays	O
a	O
"	O
Diskette	B-Device
?	O
"	O
</s>
<s>
prompt	O
if	O
a	O
bootable	O
floppy	B-Device
is	O
not	O
detected	O
.	O
</s>
<s>
On	O
powerup	O
or	O
reset	O
holding	O
down	O
the	O
key	O
will	O
boot	O
the	O
computer	O
into	O
ROM-based	O
Level	O
II	O
BASIC	O
.	O
</s>
<s>
This	O
ability	O
is	O
useful	O
if	O
the	O
disk	O
drive	O
is	O
not	O
functioning	O
and	O
cannot	O
boot	O
a	O
TRSDOS	B-Operating_System
disk	O
(	O
or	O
if	O
a	O
boot	O
disk	O
is	O
not	O
available	O
)	O
;	O
it	O
permits	O
an	O
operator	O
familiar	O
with	O
the	O
machine	O
hardware	O
to	O
perform	O
diagnostics	O
using	O
BASIC	O
's	O
PEEK	O
and	O
POKE	O
commands	O
.	O
</s>
<s>
This	O
works	O
for	O
the	O
Model	B-Device
4	I-Device
as	O
well	O
,	O
but	O
not	O
for	O
the	O
4P	O
.	O
</s>
<s>
While	O
Model	O
I	O
DOS	O
is	O
fairly	O
flexible	O
in	O
its	O
capabilities	O
,	O
Model	O
III	O
DOS	O
is	O
hard	O
coded	O
to	O
only	O
support	O
180K	O
single	O
sided	O
floppies	B-Device
,	O
a	O
problem	O
fixed	O
by	O
the	O
many	O
third	O
party	O
DOSes	O
.	O
</s>
<s>
To	O
that	O
end	O
,	O
when	O
Radio	O
Shack	O
introduced	O
hard	B-Device
disks	I-Device
for	O
the	O
TRS-80	B-Device
line	O
in	O
1982	O
,	O
the	O
company	O
licensed	O
LDOS	B-Operating_System
rather	O
than	O
attempt	O
to	O
modify	O
Model	O
III	O
DOS	O
for	O
hard	B-Device
disk	I-Device
support	O
.	O
</s>
<s>
TRSDOS	B-Operating_System
1.3	O
was	O
given	O
a	O
few	O
more	O
minor	O
updates	O
,	O
the	O
last	O
being	O
in	O
1984	O
,	O
although	O
the	O
version	O
number	O
was	O
unchanged	O
.	O
</s>
<s>
The	O
Model	O
III	O
keyboard	B-Device
lacks	O
.	O
</s>
<s>
The	O
Model	O
III	O
keyboard	B-Device
also	O
lacks	O
;	O
to	O
caps-lock	O
the	O
alpha	O
keys	O
the	O
user	O
presses	O
.	O
</s>
<s>
Under	O
LDOS	B-Operating_System
typeahead	B-Device
is	O
supported	O
.	O
</s>
<s>
Because	O
TRSDOS	B-Operating_System
1.3	O
was	O
found	O
wanting	O
by	O
many	O
users	O
,	O
Tandy	O
offered	O
(	O
at	O
added	O
cost	O
)	O
Logical	O
System	O
's	O
LDOS	B-Operating_System
Version	O
5	O
as	O
an	O
alternative	O
.	O
</s>
<s>
As	O
with	O
the	O
Model	O
I	O
,	O
other	O
third-party	O
sources	O
also	O
offered	O
TRSDOS	B-Operating_System
alternatives	O
for	O
the	O
Model	O
III	O
,	O
including	O
NewDOS	B-Operating_System
,	O
Alphabit	O
's	O
MultiDOS	O
,	O
and	O
Micro	O
Systems	O
Software	O
's	O
DOSPlus	B-Operating_System
.	O
</s>
<s>
These	O
are	O
compatible	O
with	O
TRSDOS	B-Operating_System
1.3	O
and	O
ran	O
the	O
same	O
applications	O
programs	O
,	O
but	O
offer	O
improved	O
command	O
structures	O
,	O
more	O
and	O
better	O
system	O
utilities	O
,	O
and	O
enhancements	O
to	O
the	O
Microsoft	B-Language
BASIC	I-Language
interpreter	B-Application
.	O
</s>
<s>
After	O
writing	O
the	O
original	O
Model	O
I	O
TRSDOS	B-Operating_System
,	O
Randy	O
Cook	O
began	O
work	O
on	O
his	O
own	O
DOS	O
,	O
titled	O
VTOS	O
,	O
which	O
was	O
superseded	O
by	O
LDOS	B-Operating_System
and	O
also	O
created	O
some	O
frustration	O
for	O
users	O
as	O
it	O
is	O
the	O
only	O
TRS-80	B-Device
DOS	O
to	O
be	O
copy	O
protected	O
.	O
</s>
<s>
Radio	O
Shack	O
also	O
offered	O
a	O
4K	O
version	O
with	O
Level	B-Language
I	I-Language
BASIC	I-Language
,	O
identical	O
to	O
Model	O
I	O
Level	B-Language
I	I-Language
BASIC	I-Language
,	O
but	O
with	O
the	O
addition	O
of	O
LPRINT	O
and	O
LLIST	O
commands	O
for	O
printer	O
output	O
.	O
</s>
<s>
Disk	O
upgrades	O
purchased	O
from	O
Radio	O
Shack	O
included	O
TRSDOS	B-Operating_System
1.3	O
;	O
users	O
upgrading	O
from	O
third-party	O
vendors	O
had	O
to	O
purchase	O
DOS	O
separately	O
(	O
most	O
opted	O
for	O
LDOS	B-Operating_System
or	O
DOSPlus	B-Operating_System
)	O
,	O
though	O
a	O
great	O
many	O
Model	O
III	O
applications	O
programs	O
included	O
a	O
licensed	O
copy	O
of	O
TRSDOS	B-Operating_System
1.3	O
.	O
</s>
<s>
InfoWorld	O
approved	O
of	O
the	O
Model	O
III	O
's	O
single-unit	O
design	O
,	O
simplified	O
cable	O
management	O
,	O
and	O
improvements	O
such	O
as	O
lack	O
of	O
keyboard	B-Device
bounce	O
and	O
improved	O
disk	O
reliability	O
.	O
</s>
<s>
Don	O
French	O
,	O
who	O
had	O
left	O
Radio	O
Shack	O
to	O
found	O
FMG	O
Software	O
after	O
designing	O
the	O
Model	O
I	O
,	O
expressed	O
his	O
disappointment	O
in	O
the	O
new	O
machine	O
while	O
trying	O
to	O
convert	O
CP/M	B-Application
to	O
run	O
on	O
it	O
.	O
</s>
<s>
"	O
I	O
've	O
encountered	O
numerous	O
problems	O
with	O
the	O
floppy	B-Device
drive	I-Device
and	O
its	O
interface	O
.	O
</s>
<s>
You	O
run	O
out	B-General_Concept
of	I-General_Concept
memory	I-General_Concept
before	O
you	O
get	O
going	O
.	O
</s>
<s>
The	O
usual	O
selection	O
of	O
add-ons	O
and	O
peripherals	O
available	O
for	O
the	O
Model	O
I	O
were	O
offered	O
:	O
outboard	O
floppy	B-Device
drives	I-Device
(	O
one	O
or	O
two	O
could	O
be	O
plugged	O
into	O
a	O
card-edge	O
connector	O
on	O
the	O
back	O
panel	O
)	O
,	O
an	O
outboard	O
hard	B-Device
disk	I-Device
drive	I-Device
(	O
LDOS	B-Operating_System
was	O
furnished	O
as	O
Tandy	O
's	O
hard	B-Device
drive	I-Device
OS	B-General_Concept
vice	O
TRSDOS	B-Operating_System
)	O
,	O
a	O
high-resolution	O
graphics	O
board	O
(	O
resolution	O
512	O
by	O
192	O
pixels	B-Algorithm
)	O
,	O
an	O
RS-232C	O
serial	O
port	O
on	O
an	O
internal	O
circuit	O
card	O
,	O
and	O
a	O
parallel	O
printer	O
(	O
connected	O
by	O
a	O
card-edge	O
connector	O
)	O
.	O
</s>
<s>
At	O
least	O
three	O
vendors	O
produced	O
CP/M	B-Application
modifications	O
for	O
the	O
Model	O
III	O
,	O
Omikron	O
(	O
also	O
a	O
Model	O
I	O
mod	O
)	O
,	O
Holmes	O
Engineering	O
,	O
and	O
Memory	O
Merchant	O
.	O
</s>
<s>
Options	O
were	O
available	O
for	O
upgrading	O
the	O
CRT	B-Device
to	O
the	O
CP/M	B-Application
professional	O
standard	O
of	O
80	O
columns	O
and	O
24	O
rows	O
,	O
as	O
well	O
as	O
eight	O
inch	O
floppy	B-Device
drives	I-Device
.	O
</s>
<s>
The	O
improvements	O
typically	O
included	O
internal	O
hard	B-Device
disk	I-Device
drives	I-Device
,	O
greater	O
capacity	O
floppy	B-Device
drives	I-Device
,	O
4MHz	O
Z80	B-General_Concept
speedup	O
kits	O
,	O
professional	O
grade	O
green	O
or	O
amber	O
CRT	B-Device
video	O
displays	O
,	O
better	O
DOS	O
software	O
(	O
typically	O
DOSPlus	B-Operating_System
by	O
Micro	O
Systems	O
Software	O
or	O
LDOS	B-Operating_System
by	O
Logical	O
Systems	O
)	O
including	O
the	O
all-important	O
hard	B-Device
drive	I-Device
backup	O
utilities	O
,	O
and	O
custom	O
menu-driven	O
shell	O
interfaces	O
which	O
insulated	O
non-expert	O
users	O
(	O
business	O
employees	O
)	O
from	O
the	O
DOS	O
command	O
line	O
.	O
</s>
<s>
These	O
were	O
touted	O
as	O
high	O
productivity	O
turnkey	O
systems	O
for	O
small	O
businesses	O
at	O
less	O
cost	O
than	O
competing	O
business	O
systems	O
from	O
higher-end	O
providers	O
such	O
as	O
IBM	O
and	O
DEC	O
,	O
as	O
well	O
as	O
Radio	O
Shack	O
's	O
own	O
TRS-80	B-Device
Model	I-Device
II	I-Device
.	O
</s>
<s>
The	O
successor	O
to	O
the	O
Model	O
III	O
is	O
the	O
TRS-80	B-Device
Model	I-Device
4	I-Device
released	O
in	O
April	O
1983	O
.	O
</s>
<s>
It	O
has	O
faster	O
Z80A	B-General_Concept
CPU	B-General_Concept
,	O
a	O
larger	O
video	O
display	O
80	O
columns	O
x	O
24	O
rows	O
with	O
reverse	O
video	O
,	O
bigger	O
keyboard	B-Device
,	O
internal	O
speaker	O
,	O
and	O
its	O
64	O
KB	O
of	O
RAM	O
can	O
be	O
upgraded	O
to	O
128	O
KB	O
of	O
bank-switched	B-General_Concept
RAM	O
.	O
</s>
<s>
The	O
display	O
can	O
be	O
upgraded	O
with	O
a	O
high	O
resolution	O
graphics	O
card	O
yielding	O
640240	O
pixels	B-Algorithm
.	O
</s>
<s>
The	O
Model	B-Device
4	I-Device
is	O
fully	O
compatible	O
with	O
Model	O
III	O
and	O
CP/M	B-Application
application	O
software	O
.	O
</s>
<s>
A	O
diskless	O
Model	B-Device
4	I-Device
(	O
with	O
16	O
KB	O
RAM	O
and	O
Level	O
II	O
BASIC	O
)	O
cost	O
,	O
with	O
64	O
KB	O
RAM	O
and	O
one	O
single-sided	O
180K	O
disk	O
drive	O
,	O
and	O
two	O
drives	O
with	O
RS-232C	O
;	O
an	O
upgrade	O
for	O
Model	O
III	O
owners	O
cost	O
and	O
provided	O
a	O
new	O
motherboard	B-Device
and	O
keyboard	B-Device
.	O
</s>
<s>
The	O
Model	B-Device
4	I-Device
includes	O
all	O
of	O
the	O
Model	O
III	O
's	O
hardware	O
,	O
port	O
assignments	O
,	O
and	O
operating	O
modes	O
,	O
making	O
it	O
100%	O
compatible	O
.	O
</s>
<s>
Model	O
III	O
programs	O
running	O
on	O
a	O
Model	B-Device
4	I-Device
can	O
access	O
the	O
Model	B-Device
4	I-Device
's	O
added	O
hardware	O
features	O
(	O
like	O
4MHz	O
clock	O
rate	O
,	O
bigger	O
video	O
screen	O
and	O
keyboard	B-Device
,	O
banked	O
RAM	O
above	O
64	O
KB	O
)	O
.	O
</s>
<s>
It	O
is	O
functionally	O
the	O
same	O
as	O
the	O
dual-drive	O
desktop	O
model	O
but	O
lacks	O
the	O
card	O
edge	O
connector	O
for	O
two	O
outboard	O
diskette	B-Device
drives	O
and	O
for	O
cassette	B-Device
tape	I-Device
interface	O
.	O
</s>
<s>
The	O
Model	O
4D	O
with	O
bundled	O
Deskmate	B-Device
productivity	O
suite	O
was	O
introduced	O
in	O
early	O
1985	O
.	O
</s>
<s>
It	O
has	O
a	O
revised	O
CPU	B-General_Concept
board	O
using	O
faster	O
gate	O
array	O
logic	O
which	O
includes	O
the	O
floppy	B-Device
controller	O
and	O
RS-232C	O
circuitry	O
,	O
all	O
on	O
a	O
single	O
board	O
.	O
</s>
<s>
The	O
computer	O
has	O
two	O
internal	O
double-sided	O
diskette	B-Device
drives	O
,	O
and	O
is	O
the	O
last	O
model	O
descended	O
from	O
the	O
1977	O
Model	O
I	O
.	O
</s>
