<s>
The	O
TRS-80	B-Device
Model	I-Device
II	I-Device
is	O
a	O
computer	O
system	O
launched	O
by	O
Tandy	O
in	O
October	O
1979	O
,	O
and	O
targeted	O
at	O
the	O
small-business	O
market	O
.	O
</s>
<s>
It	O
is	O
not	O
an	O
upgrade	O
of	O
the	O
original	O
TRS-80	B-Device
Model	I-Device
I	I-Device
,	O
but	O
a	O
new	O
system	O
.	O
</s>
<s>
The	O
Model	O
II	O
was	O
succeeded	O
by	O
the	O
compatible	O
TRS-80	B-Device
Model	O
12	O
,	O
Model	O
16	O
,	O
Model	O
16B	O
,	O
and	O
the	O
Tandy	O
6000	O
.	O
</s>
<s>
Tandy	O
was	O
surprised	O
at	O
the	O
strong	O
demand	O
for	O
the	O
TRS-80	B-Device
Model	I-Device
I	I-Device
from	O
business	O
purchasers	O
.	O
</s>
<s>
Tandy	O
advertised	O
the	O
Model	O
II	O
as	O
"	O
a	O
business	O
computer	O
—	O
not	O
a	O
hobby	O
,	O
'	O
home	O
 '	O
or	O
personal	B-Device
computer	I-Device
"	O
.	O
</s>
<s>
It	O
claimed	O
that	O
the	O
computer	O
was	O
"	O
ideal	O
for	O
a	O
small	O
business	O
,	O
and	O
also	O
'	O
just	O
right	O
 '	O
for	O
many	O
time-consuming	O
jobs	O
within	O
larger	O
businesses	O
"	O
,	O
including	O
those	O
with	O
mainframes	B-Architecture
or	O
minicomputers	B-Architecture
.	O
</s>
<s>
As	O
a	O
professional	O
business	O
machine	O
,	O
the	O
Model	O
II	O
used	O
state-of-the-art	O
hardware	O
and	O
had	O
numerous	O
features	O
not	O
found	O
in	O
the	O
primitive	O
Model	O
I	O
such	O
as	O
the	O
high-speed	O
(	O
for	O
the	O
time	O
)	O
4MHz	O
Z80A	B-General_Concept
,	O
DMA	O
,	O
vectored	O
interrupts	O
,	O
a	O
detachable	O
keyboard	O
with	O
two	O
function	O
keys	O
and	O
numeric	O
keypad	O
,	O
and	O
port	O
instead	O
of	O
memory-mapped	O
I/O	O
.	O
</s>
<s>
The	O
video	O
memory	O
could	O
be	O
banked	O
out	O
of	O
Z80	B-General_Concept
memory	O
,	O
so	O
that	O
the	O
entire	O
64	O
KB	O
address	O
space	O
could	O
be	O
used	O
for	O
main	O
memory	O
.	O
</s>
<s>
The	O
Model	O
II	O
ran	O
the	O
TRSDOS	B-Operating_System
operating	O
system	O
(	O
renamed	O
to	O
TRSDOS-II	O
starting	O
with	O
version	O
4.0	O
)	O
and	O
BASIC	O
.	O
</s>
<s>
This	O
was	O
somewhat	O
mitigated	O
by	O
the	O
availability	O
of	O
the	O
CP/M	B-Application
operating	I-Application
system	I-Application
for	O
the	O
Model	O
II	O
from	O
third	O
parties	O
such	O
as	O
Pickles	O
&	O
Trout	O
.	O
</s>
<s>
Unlike	O
the	O
Model	O
I/III	O
,	O
the	O
Model	O
II	O
's	O
memory	O
map	O
is	O
compatible	O
with	O
standard	O
CP/M	B-Application
-80	I-Application
.	O
</s>
<s>
The	O
floppy	O
controller	O
in	O
the	O
Model	O
II	O
was	O
a	O
double-density	O
,	O
soft-sector	O
unit	O
based	O
on	O
the	O
WD	B-Device
1791	I-Device
floppy	I-Device
controller	I-Device
.	O
</s>
<s>
The	O
disk	O
format	O
on	O
the	O
Model	O
II	O
closely	O
followed	O
the	O
IBM	B-Device
3740	I-Device
standard	O
,	O
which	O
specified	O
77	O
tracks	O
,	O
26	O
sectors	O
per	O
track	O
,	O
soft	O
sector	O
formatting	O
,	O
and	O
a	O
sector	O
size	O
of	O
128	O
bytes	O
for	O
a	O
formatted	O
capacity	O
of	O
about	O
250k	O
,	O
however	O
the	O
Model	O
II	O
had	O
a	O
double	O
density	O
controller	O
,	O
so	O
the	O
disk	O
format	O
used	O
256	O
byte	O
sectors	O
and	O
formatted	O
capacity	O
was	O
about	O
492k	O
.	O
</s>
<s>
The	O
Model	O
II	O
was	O
similar	O
to	O
an	O
S-100	B-Architecture
machine	O
in	O
that	O
it	O
featured	O
a	O
passive	O
backplane	O
with	O
eight	O
expansion	O
slots	O
;	O
four	O
of	O
these	O
were	O
normally	O
occupied	O
by	O
the	O
CPU	O
card	O
,	O
floppy	O
controller	O
,	O
keyboard/video	O
card	O
,	O
and	O
RAM	O
.	O
</s>
<s>
Although	O
the	O
expansion	O
slots	O
look	O
similar	O
to	O
an	O
S-100	B-Architecture
slot	O
,	O
they	O
were	O
a	O
proprietary	O
design	O
and	O
could	O
not	O
be	O
used	O
with	O
S-100	B-Architecture
boards	O
.	O
</s>
<s>
Various	O
expansion	O
cards	O
for	O
the	O
remaining	O
four	O
slots	O
included	O
a	O
hard	O
disk	O
controller	O
,	O
networking	O
card	O
,	O
a	O
68000	B-Device
CPU	O
board	O
that	O
could	O
address	O
up	O
to	O
256	O
KB	O
memory	O
,	O
and	O
a	O
board	O
for	O
pixel-addressable	O
graphics	O
with	O
640	O
by	O
240	O
resolution	O
.	O
</s>
<s>
The	O
Model	O
II	O
architecture	O
theoretically	O
supported	O
up	O
to	O
512K	O
RAM	O
via	O
a	O
bank-switchable	B-General_Concept
upper	O
32K	O
page	O
segment	O
(	O
up	O
to	O
fifteen	O
32K	O
pages	O
were	O
supported	O
)	O
.	O
</s>
<s>
This	O
deficiency	O
was	O
rectified	O
with	O
the	O
Model	O
12	O
,	O
which	O
could	O
accommodate	O
up	O
to	O
768	O
KB	O
RAM	O
using	O
the	O
newer	O
4164	O
DRAM	O
chips	O
and	O
a	O
revised	O
bank-switching	B-General_Concept
scheme	O
.	O
</s>
<s>
A	O
special-purpose	O
expansion	O
card	O
was	O
the	O
64K	O
Memory	O
Expansion	O
Board	O
(	O
catalog	O
number	O
26-4105	O
)	O
which	O
allowed	O
the	O
Model	O
II	O
(	O
without	O
the	O
expensive	O
Model	O
16	O
upgrade	O
)	O
to	O
run	O
a	O
special	O
version	O
of	O
the	O
Visicalc	B-Application
spreadsheet	O
called	O
Enhanced	O
Visicalc	B-Application
.	O
</s>
<s>
This	O
made	O
available	O
larger	O
worksheets	O
by	O
using	O
banked	O
memory	O
beyond	O
the	O
Z80	B-General_Concept
's	O
base	O
64	O
KB	O
.	O
</s>
<s>
Some	O
of	O
the	O
technical	O
advances	O
first	O
introduced	O
on	O
the	O
Model	O
II	O
such	O
as	O
the	O
WD	B-Device
1791	I-Device
floppy	I-Device
controller	I-Device
and	O
the	O
improved	O
video	O
circuitry	O
would	O
later	O
go	O
into	O
the	O
Model	O
III	O
.	O
</s>
<s>
In	O
addition	O
,	O
CP/M	B-Application
versions	O
of	O
Infocom	O
text	O
adventures	O
would	O
run	O
.	O
</s>
<s>
While	O
Model	O
I/III	O
BASIC	O
include	O
a	O
startup	O
prompt	O
asking	O
if	O
the	O
user	O
would	O
like	O
to	O
reduce	O
BASIC	O
's	O
memory	O
area	O
(	O
typically	O
done	O
if	O
some	O
memory	O
is	O
to	O
be	O
reserved	O
for	O
machine	O
language	O
routines	O
)	O
,	O
Model	O
II	O
BASIC	O
instead	O
has	O
this	O
feature	O
as	O
a	O
command	O
line	O
option	O
(	O
M:address	O
)	O
when	O
started	O
from	O
the	O
TRS-DOS	B-Operating_System
prompt	O
.	O
</s>
<s>
The	O
SYSTEM	O
command	O
,	O
used	O
to	O
exit	O
BASIC	O
,	O
may	O
also	O
be	O
used	O
to	O
"	O
pass	O
"	O
a	O
command	O
to	O
TRS-DOS	B-Operating_System
without	O
exiting	O
and	O
losing	O
the	O
program	O
currently	O
in	O
memory	O
;	O
this	O
is	O
most	O
commonly	O
done	O
for	O
tasks	O
such	O
as	O
viewing	O
the	O
disk	O
directory	O
.	O
</s>
<s>
It	O
was	O
possible	O
to	O
regain	O
most	O
of	O
this	O
functionality	O
by	O
using	O
the	O
extremely	O
similar	O
MBASIC	O
provided	O
with	O
CP/M	B-Application
.	O
</s>
<s>
Microsoft	O
made	O
available	O
its	O
Fortran	B-Application
,	O
Cobol	B-Application
and	O
BASIC	O
compilers	O
,	O
as	O
well	O
as	O
its	O
MACRO-80	O
assembler	O
.	O
</s>
<s>
Some	O
were	O
produced	O
in-house	O
(	O
like	O
the	O
Scripsit	B-Protocol
word	O
processor	O
)	O
,	O
others	O
licensed	O
and	O
branded	O
as	O
Radio	O
Shack	O
products	O
(	O
like	O
the	O
Profile	O
database	O
)	O
,	O
and	O
still	O
others	O
marketed	O
by	O
Radio	O
Shack	O
,	O
such	O
as	O
VisiCalc	B-Application
.	O
</s>
<s>
The	O
company	O
also	O
offered	O
products	O
facilitating	O
data	O
transfer	O
with	O
IBM	O
mainframe	B-Architecture
computers	I-Architecture
.	O
</s>
<s>
The	O
Model	O
II	O
was	O
replaced	O
in	O
1982	O
by	O
the	O
TRS-80	B-Device
Model	O
12	O
,	O
which	O
has	O
half-height	O
(	O
"	O
thinline	O
"	O
)	O
double-sided	O
floppy	O
drives	O
,	O
and	O
integrates	O
most	O
of	O
the	O
Model	O
II	O
electronics	O
into	O
a	O
single	O
main	O
board	O
.	O
</s>
<s>
The	O
TRS-80	B-Device
Model	O
16	O
came	O
out	O
in	O
February	O
1982	O
as	O
the	O
follow-on	O
to	O
the	O
Model	O
II	O
;	O
an	O
upgrade	O
kit	O
was	O
available	O
for	O
Model	O
II	O
systems	O
.	O
</s>
<s>
The	O
Model	O
16	O
added	O
a	O
6MHz	O
,	O
16/32	O
-bit	O
Motorola	B-Device
68000	I-Device
processor	I-Device
and	O
memory	O
card	O
,	O
keeping	O
the	O
original	O
Z80	B-General_Concept
as	I-General_Concept
an	O
I/O	O
processor	O
,	O
or	O
as	O
the	O
main	O
processor	O
when	O
8-bit	O
Model	O
II	O
software	O
was	O
loaded	O
.	O
</s>
<s>
The	O
Model	O
16	O
can	O
run	O
either	O
TRSDOS-16	O
or	O
TRS-Xenix	B-Application
,	O
a	O
variant	O
of	O
Xenix	B-Application
,	O
Microsoft	O
's	O
version	O
of	O
UNIX	O
.	O
</s>
<s>
TRSDOS-16	O
is	O
a	O
TRSDOS	B-Operating_System
II-4.1	O
application	O
providing	O
a	O
68000	B-Device
interface	O
and	O
support	O
for	O
up	O
to	O
three	O
users	O
,	O
with	O
no	O
additional	O
features	O
and	O
little	O
compatible	O
software	O
.	O
</s>
<s>
68000	B-Device
functionality	O
was	O
added	O
as	O
an	O
extension	O
,	O
loading	O
68000	B-Device
code	O
into	O
the	O
68000	B-Device
memory	O
via	O
a	O
shared	O
memory	O
window	O
with	O
the	O
Z80	B-General_Concept
.	O
</s>
<s>
Five	O
months	O
after	O
its	O
introduction	O
,	O
the	O
computer	O
still	O
had	O
no	O
TRSDOS-16	O
applications	O
;	O
owners	O
had	O
to	O
run	O
Model	O
II	O
or	O
CP/M	B-Application
software	O
and	O
applications	O
.	O
</s>
<s>
Its	O
release	O
forced	O
the	O
few	O
developers	O
of	O
Model	O
II	O
software	O
to	O
"	O
start	O
all	O
over	O
again	O
"	O
,	O
Green	O
said	O
,	O
because	O
customers	O
would	O
not	O
want	O
to	O
run	O
Z80	B-General_Concept
software	O
on	O
the	O
Model	O
16	O
.	O
</s>
<s>
Tandy	O
admitted	O
that	O
it	O
should	O
have	O
encouraged	O
third-party	O
software	O
development	O
,	O
which	O
resulted	O
in	O
the	O
killer	O
app	O
VisiCalc	B-Application
for	O
the	O
Apple	B-Device
II	I-Device
.	O
</s>
<s>
In	O
1983	O
VisiCorp	O
produced	O
an	O
update	O
of	O
Visicalc	B-Application
which	O
Tandy	O
sold	O
for	O
the	O
Model	O
16	O
called	O
Enhanced	O
VisiCalc	B-Application
.	O
</s>
<s>
This	O
version	O
runs	O
on	O
the	O
Z80	B-General_Concept
and	O
uses	O
banked	O
memory	O
beyond	O
the	O
base	O
64	O
KB	O
for	O
larger	O
worksheets	O
.	O
</s>
<s>
Rumors	O
stated	O
that	O
Tandy	O
would	O
offer	O
Xenix	B-Application
or	O
another	O
third-party	O
operating	O
system	O
for	O
the	O
computer	O
.	O
</s>
<s>
In	O
early	O
1983	O
the	O
company	O
indeed	O
switched	O
to	O
Xenix	B-Application
,	O
and	O
offered	O
it	O
for	O
free	O
to	O
existing	O
customers	O
;	O
by	O
mid-1983	O
an	O
estimated	O
5,000	O
of	O
30,000	O
Model	O
16s	O
ran	O
Xenix	B-Application
.	O
</s>
<s>
Xenix	B-Application
was	O
based	O
on	O
UNIX	B-Operating_System
System	I-Operating_System
III	I-Operating_System
,	O
also	O
supported	O
up	O
to	O
three	O
users	O
,	O
and	O
was	O
more	O
established	O
.	O
</s>
<s>
With	O
Xenix	B-Application
,	O
the	O
Model	O
16	O
family	O
became	O
a	O
popular	O
system	O
for	O
small	O
business	O
,	O
with	O
a	O
relatively	O
large	O
library	O
of	O
business	O
and	O
office	B-Application
automation	I-Application
software	I-Application
.	O
</s>
<s>
Tandy	O
offered	O
multi-user	O
word	O
processing	O
(	O
Scripsit	B-Protocol
16	O
)	O
,	O
spreadsheet	O
(	O
Multiplan	B-Device
)	O
,	O
and	O
a	O
3GL	O
"	O
database	O
"	O
(	O
Profile	O
16	O
,	O
later	O
upgraded	O
to	O
filePro	B-Application
16+	O
)	O
,	O
as	O
well	O
as	O
an	O
accounting	O
suite	O
with	O
optional	O
COBOL	B-Application
source	O
for	O
customization	O
.	O
</s>
<s>
RM-COBOL	O
,	O
BASIC	O
,	O
and	O
C	O
were	O
available	O
for	O
programming	O
,	O
with	O
Unify	O
and	O
Informix	B-Application
offered	O
as	O
relational	O
databases	O
.	O
</s>
<s>
TRS-Xenix	B-Application
was	O
notable	O
for	O
being	O
a	O
master/slave	O
implementation	O
,	O
with	O
all	O
I/O	O
being	O
performed	O
by	O
the	O
Z80	B-General_Concept
while	O
all	O
processing	O
was	O
done	O
within	O
the	O
otherwise	O
I/O	O
-free	O
68000	B-Device
subsystem	O
.	O
</s>
<s>
The	O
Model	O
16	O
evolved	O
into	O
the	O
TRS-80	B-Device
Model	O
16B	O
with	O
256	O
KB	O
in	O
July	O
1983	O
,	O
and	O
later	O
in	O
1985	O
the	O
Tandy	O
6000	O
,	O
gaining	O
an	O
internal	O
hard	O
drive	O
along	O
the	O
way	O
and	O
switching	O
to	O
an	O
8MHz	O
68000	B-Device
.	O
</s>
<s>
The	O
Model	O
6000	O
was	O
referred	O
to	O
simply	O
as	O
the	O
Tandy	O
6000	O
due	O
to	O
a	O
marketing	O
decision	O
to	O
move	O
away	O
from	O
the	O
Radio	O
Shack	O
and	O
TRS-80	B-Device
badges	O
.	O
</s>
<s>
By	O
1988	O
,	O
Radio	O
Shack	O
had	O
begun	O
offering	O
IBM-compatible	O
386	O
PCs	B-Device
for	O
their	O
professional	O
line	O
and	O
finally	O
retired	O
the	O
Model	O
II	O
family	O
.	O
</s>
<s>
BYTEs	O
review	O
in	O
January	O
1984	O
stated	O
that	O
"	O
the	O
Model	O
16B	O
is	O
a	O
fairly	O
well-implemented	O
and	O
apparently	O
well-supported	O
Xenix	B-Application
system	O
"	O
that	O
would	O
likely	O
receive	O
much	O
support	O
from	O
software	O
developers	O
.	O
</s>
<s>
While	O
criticizing	O
Xenix	B-Application
's	O
user	O
unfriendliness	O
for	O
small	O
business	O
customers	O
,	O
and	O
wondering	O
"	O
whether	O
Radio	O
Shack	O
can	O
or	O
will	O
invest	O
"	O
in	O
training	O
on	O
the	O
very	O
sophisticated	O
operating	O
system	O
for	O
its	O
dealers	O
,	O
they	O
concluded	O
that	O
the	O
Model	O
16B	O
"	O
deserves	O
serious	O
consideration	O
"	O
.	O
</s>
