<s>
The	O
Xerox	B-Device
820	I-Device
Information	O
Processor	O
is	O
an	O
8-bit	O
desktop	O
computer	O
sold	O
by	O
Xerox	O
in	O
the	O
early	O
1980s	O
.	O
</s>
<s>
The	O
computer	O
runs	O
under	O
the	O
CP/M	B-Application
operating	I-Application
system	I-Application
and	O
uses	O
floppy	B-Device
disk	I-Device
drives	I-Device
for	O
mass	O
storage	O
.	O
</s>
<s>
The	O
microprocessor	O
board	O
is	O
a	O
licensed	O
variant	O
of	O
the	O
Big	B-Device
Board	I-Device
computer	O
.	O
</s>
<s>
Xerox	O
introduced	O
the	O
820	O
in	O
June	O
1981	O
for	O
$	O
2,995	O
with	O
two	O
-inch	O
single-density	O
disk	O
drives	O
with	O
81K	O
of	O
capacity	O
per	O
diskette	B-Device
,	O
or	O
$	O
3,795	O
with	O
two	O
8-inch	O
drives	O
with	O
241K	O
capacity	O
.	O
</s>
<s>
To	O
beat	O
the	O
IBM	B-Device
PC	I-Device
to	O
market	O
Xerox	O
created	O
little	O
of	O
the	O
computer	O
's	O
design	O
;	O
it	O
is	O
based	O
on	O
the	O
Ferguson	B-Device
Big	I-Device
Board	I-Device
computer	O
kit	O
and	O
other	O
off-the-shelf	O
components	O
,	O
including	O
a	O
Zilog	B-General_Concept
Z80	I-General_Concept
processor	O
clocked	O
at	O
2.5MHz	O
,	O
and	O
64	O
KB	O
of	O
RAM	B-Architecture
.	O
</s>
<s>
Xerox	O
chose	O
CP/M	B-Application
as	O
its	O
operating	O
system	O
because	O
of	O
the	O
large	O
software	O
library	O
—	O
The	O
820	O
is	O
compatible	O
with	O
all	O
Big	B-Device
Board	I-Device
software	O
—	O
and	O
sold	O
a	O
customized	O
version	O
of	O
WordStar	B-Application
for	O
$495	O
,	O
although	O
by	O
1982	O
the	O
company	O
offered	O
the	O
standard	O
version	O
for	O
the	O
same	O
price	O
.	O
</s>
<s>
The	O
Xerox	O
820-II	O
followed	O
in	O
1982	O
,	O
featuring	O
a	O
Z80A	B-General_Concept
processor	O
clocked	O
at	O
4.0MHz	O
.	O
</s>
<s>
Hardware	O
:	O
The	O
processor	O
board	O
is	O
located	O
inside	O
the	O
CRT	B-Device
unit	O
,	O
and	O
includes	O
the	O
Z80A	B-General_Concept
,	O
64	O
KB	O
of	O
RAM	B-Architecture
and	O
a	O
boot	O
ROM	B-Device
which	O
enables	O
booting	O
from	O
any	O
of	O
the	O
supported	O
external	O
drives	O
in	O
8-bit	O
mode	O
.	O
</s>
<s>
Screen	O
:	O
The	O
display	O
is	O
a	O
24-line	O
,	O
80-character	O
(	O
7×10	O
dot	O
matrix	O
)	O
white-on-black	O
monochrome	O
CRT	B-Device
,	O
with	O
software-selectable	O
variations	O
such	O
as	O
reverse	B-General_Concept
video	I-General_Concept
,	O
blinking	O
,	O
low-intensity	O
(	O
equivalent	O
to	O
grey	O
text	O
)	O
,	O
and	O
4×	O
4-resolution	O
graphics	O
.	O
</s>
<s>
Communication	O
ports	O
:	O
These	O
include	O
two	O
25-pin	O
RS-232	O
serial	O
ports	O
(	O
including	O
one	O
intended	O
for	O
a	O
Xerox	O
620	O
or	O
630	O
printer	O
or	O
compatible	O
,	O
and	O
one	O
intended	O
for	O
a	O
modem	O
)	O
,	O
and	O
two	O
optional	O
parallel	O
ports	O
which	O
can	O
be	O
added	O
via	O
an	O
internal	O
pin	B-Protocol
header	I-Protocol
,	O
usable	O
with	O
a	O
Xerox	O
or	O
other	O
cable	O
.	O
</s>
<s>
Keyboard	B-Device
:	O
A	O
bulky	O
96-character	O
ASCII	O
keyboard	B-Device
with	O
a	O
10-key	O
numeric	O
keypad	O
and	O
a	O
cursor	O
diamond	O
which	O
otherwise	O
defaults	O
to	O
Ctrl-A	O
to	O
Ctrl-D	O
.	O
</s>
<s>
It	O
also	O
includes	O
and	O
keys	O
,	O
and	O
is	O
attached	O
to	O
the	O
back	O
of	O
the	O
CRT	B-Device
unit	O
by	O
a	O
thick	O
cable	O
.	O
</s>
<s>
Software	O
:	O
A	O
typical	O
820-II	O
comes	O
with	O
CP/M	B-Application
2.2	O
,	O
diagnostic	O
software	O
,	O
WordStar	B-Application
,	O
and	O
Microsoft	O
's	O
BASIC-80	O
programming	O
language	O
.	O
</s>
<s>
a	O
SASI	O
hard	O
disk/floppy	O
disk	O
I/O	O
card	O
,	O
which	O
can	O
control	O
one	O
external	O
8	B-Device
"	I-Device
hard	B-Device
drive	I-Device
and	O
one	O
to	O
three	O
external	O
8	B-Device
"	I-Device
floppy	B-Device
drives	I-Device
(	O
these	O
being	O
either	O
single	O
-	O
or	O
double-sided	B-Architecture
,	O
and	O
either	O
single	O
-	O
or	O
double-density	O
)	O
.	O
</s>
<s>
The	O
820-II	O
has	O
a	O
processor	O
expansion	O
capability	O
,	O
which	O
optionally	O
supports	O
a	O
16-bit	O
Intel	B-General_Concept
8086	I-General_Concept
processor	O
card	O
with	O
its	O
own	O
128	O
KB	O
or	O
256	O
KB	O
of	O
RAM	B-Architecture
(	O
the	O
16-bit	O
processor	O
card	O
uses	O
the	O
on-mainboard	O
Z80A	B-General_Concept
for	O
all	O
peripheral	O
I/O	O
operations	O
,	O
therefore	O
the	O
8086	B-General_Concept
behaves	O
more	O
like	O
a	O
co-processor	O
)	O
.	O
</s>
<s>
The	O
820-II	O
'	O
s	O
16-bit	O
processor	O
card	O
features	O
a	O
true	O
16-bit	O
8086	B-General_Concept
processor	O
,	O
not	O
an	O
8/16	O
-bit	O
8088	O
processor	O
as	O
on	O
the	O
contemporary	O
IBM	B-Device
PC	I-Device
.	O
</s>
<s>
The	O
16-bit	O
processor	O
card	O
is	O
,	O
however	O
,	O
limited	O
to	O
128	O
KB	O
of	O
DRAM	O
(	O
256	O
KB	O
,	O
maximum	O
,	O
if	O
incorporating	O
a	O
rather	O
rare	O
RAM	B-Architecture
"	O
daughter	O
"	O
card	O
)	O
.	O
</s>
<s>
Flipping	O
the	O
820-II	O
'	O
s	O
console	O
between	O
8-bit	O
and	O
16-bit	O
modes	O
on	O
an	O
820-II	O
which	O
is	O
equipped	O
with	O
the	O
optional	O
16-bit	O
processor	O
card	O
is	O
accomplished	O
by	O
a	O
keyboard	B-Device
control	O
command	O
.	O
</s>
<s>
Xerox	O
820-II	O
component	O
parts	O
were	O
available	O
from	O
Xerox	O
outlet	O
stores	O
at	O
quite	O
reasonable	O
prices	O
,	O
and	O
it	O
was	O
not	O
uncommon	O
to	O
convert	O
surplus	O
(	O
but	O
new	O
)	O
128	O
KB	O
16-bit	O
processor	O
cards	O
to	O
512	O
KB	O
by	O
the	O
substitution	O
of	O
sixteen	O
41256	O
DRAM	O
chips	O
for	O
the	O
card	O
's	O
usual	O
sixteen	O
4164	O
DRAM	O
chips	O
(	O
both	O
are	O
16-pin	O
DIPs	O
—	O
pin	O
1	O
is	O
unused	O
on	O
a	O
4164	O
and	O
becomes	O
A8	O
on	O
a	O
41256	O
)	O
,	O
plus	O
the	O
addition	O
of	O
two	O
ICs	O
(	O
one	O
74F02	O
and	O
one	O
74F08	O
,	O
or	O
two	O
user-modified	O
PALs	O
)	O
for	O
controlling	O
the	O
41256	O
's	O
9th	O
address	O
row	O
and	O
column	O
(	O
not	O
found	O
on	O
4164s	O
)	O
,	O
thereby	O
achieving	O
a	O
four-times	O
increase	O
in	O
RAM	B-Architecture
without	O
the	O
use	O
of	O
a	O
"	O
daughter	O
"	O
card	O
(	O
which	O
can	O
only	O
achieve	O
a	O
two-times	O
increase	O
in	O
RAM	B-Architecture
)	O
.	O
</s>
<s>
A	O
simple	O
modification	O
to	O
the	O
820-II	O
'	O
s	O
BIOS	O
initialization	O
code	O
was	O
developed	O
to	O
move	O
the	O
BIOS	O
image	O
up	O
to	O
the	O
top	O
of	O
the	O
512	O
KB	O
RAM	B-Architecture
area	O
,	O
thereby	O
giving	O
the	O
applications	O
maximum	O
contiguous	O
RAM	B-Architecture
.	O
</s>
<s>
Otherwise	O
,	O
the	O
512	O
KB	O
of	O
the	O
converted	O
processor	O
card	O
is	O
segmented	O
into	O
a	O
lower	O
128	O
KB	O
segment	O
,	O
and	O
an	O
upper	O
384	O
KB	O
segment	O
,	O
but	O
CP/M	B-Operating_System
-86	I-Operating_System
was	O
designed	O
to	O
handle	O
such	O
segmented	O
RAM	B-Architecture
,	O
so	O
this	O
BIOS	O
modification	O
is	O
optional	O
,	O
although	O
desirable	O
.	O
</s>
<s>
Unlike	O
much	O
later	O
processors	O
from	O
Intel	O
,	O
and	O
others	O
,	O
which	O
offers	O
both	O
segmented	O
and	O
"	O
flat	O
"	O
addressing	O
,	O
the	O
8086	B-General_Concept
(	O
and	O
the	O
8088	O
)	O
offers	O
only	O
segmented	O
addressing	O
,	O
with	O
each	O
segment	O
limited	O
to	O
64	O
KB	O
.	O
</s>
<s>
By	O
effective	O
utilization	O
of	O
the	O
four	O
available	O
segment	O
registers	O
,	O
Code	O
,	O
Data	O
,	O
Stack	O
and	O
Extra	O
,	O
the	O
512	O
KB	O
address	O
space	O
possible	O
with	O
the	O
modified	O
820-II	O
8086	B-General_Concept
processor	O
card	O
can	O
be	O
very	O
effectively	O
managed	O
,	O
although	O
in	O
64	O
KB	O
chunks	O
.	O
</s>
<s>
Much	O
CP/M	B-Application
software	O
uses	O
the	O
Xerox	B-Device
820	I-Device
's	O
disk	O
format	O
,	O
and	O
other	O
computers	O
such	O
as	O
the	O
Kaypro	O
II	O
are	O
compatible	O
with	O
it	O
.	O
</s>
<s>
The	O
CRT	B-Device
unit	O
contains	O
the	O
processor	O
,	O
and	O
a	O
large	O
port	O
on	O
the	O
back	O
connected	O
via	O
heavy	O
cable	O
to	O
a	O
disk	O
drive	O
,	O
allowing	O
a	O
wide	O
variety	O
of	O
configurations	O
.	O
</s>
<s>
The	O
system	O
can	O
function	O
to	O
a	O
limited	O
extent	O
without	O
having	O
to	O
load	O
a	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
:	O
the	O
system	B-Application
monitor	I-Application
in	O
ROM	B-Device
allows	O
,	O
at	O
boot-up	O
,	O
a	O
variety	O
of	O
uses	O
via	O
one-letter	O
commands	O
followed	O
by	O
attributes	O
.	O
</s>
<s>
A	O
user	O
normally	O
uses	O
the	O
"	O
(	O
L	O
)	O
oad	O
"	O
command	O
to	O
load	O
a	O
bootstrap	O
loader	O
(	O
i.e.	O
,	O
for	O
CP/M	B-Application
)	O
from	O
a	O
floppy	B-Device
or	O
the	O
fixed	B-Device
disk	I-Device
.	O
</s>
<s>
Further	O
,	O
(	O
documented	O
)	O
calls	O
to	O
BOS	O
subroutines	O
allows	O
a	O
skilled	O
user	O
or	O
program	O
to	O
restart	O
the	O
system	O
,	O
perform	O
disk	O
operations	O
,	O
take	O
keyboard	B-Device
input	O
,	O
or	O
write	O
to	O
the	O
display	O
.	O
</s>
<s>
The	O
Model	O
16/8	O
,	O
introduced	O
in	O
May	O
1983	O
,	O
has	O
dual	O
CPUs	O
,	O
an	O
8-bit	O
Z80	B-General_Concept
and	O
16-bit	O
Intel	B-General_Concept
8086	I-General_Concept
,	O
which	O
can	O
be	O
booted	O
jointly	O
or	O
separately	O
.	O
</s>
<s>
The	O
operating	O
system	O
is	O
8-bit	O
CP/M	B-Application
-80	I-Application
and	O
16-bit	O
CP/M	B-Operating_System
-86	I-Operating_System
,	O
and	O
the	O
computer	O
was	O
supplied	O
with	O
the	O
WordStar	B-Application
word	B-General_Concept
processor	I-General_Concept
and	O
dBase	B-Application
II	I-Application
database	B-Application
management	I-Application
system	I-Application
.	O
</s>
<s>
It	O
has	O
double	O
8	B-Device
"	I-Device
floppy	B-Device
disk	I-Device
drives	I-Device
,	O
a	O
12	O
"	O
monochrome	O
monitor	O
and	O
a	O
daisywheel	O
printer	O
.	O
</s>
<s>
Later	O
in	O
1984	O
double	O
5.25	B-Device
"	I-Device
floppy	B-Device
disk	I-Device
drives	I-Device
,	O
a	O
portrait-size	O
blue	O
monitor	O
,	O
and	O
a	O
laser	O
printer	O
were	O
offered	O
.	O
</s>
<s>
Flipping	O
the	O
8/16	O
'	O
s	O
console	O
between	O
8	O
bit	O
and	O
16	O
bit	O
modes	O
is	O
accomplished	O
by	O
a	O
simple	O
keyboard	B-Device
control	O
command	O
.	O
</s>
<s>
While	O
less	O
expensive	O
than	O
dedicated	B-General_Concept
word	I-General_Concept
processors	I-General_Concept
such	O
as	O
the	O
Xerox	O
860	O
,	O
the	O
820	O
was	O
expensive	O
and	O
slow	O
compared	O
to	O
personal	O
computers	O
;	O
one	O
month	O
after	O
its	O
release	O
,	O
the	O
Osborne	B-Device
1	I-Device
—	O
faster	O
,	O
portable	O
,	O
and	O
with	O
bundled	O
software	O
worth	O
more	O
than	O
—	O
appeared	O
,	O
while	O
Xerox	O
charged	O
for	O
the	O
required	O
CP/M	B-Application
software	O
.	O
</s>
<s>
The	O
820	O
did	O
not	O
use	O
Xerox	O
PARC	O
's	O
sophisticated	O
technology	O
that	O
influenced	O
the	O
Apple	B-Device
Macintosh	I-Device
.	O
</s>
<s>
InfoWorld	O
in	O
1982	O
stated	O
that	O
"	O
The	O
considerable	O
virtues	O
of	O
the	O
Xerox	B-Device
820	I-Device
lie	O
mostly	O
in	O
its	O
use	O
of	O
the	O
Big	B-Device
Board	I-Device
design	O
—	O
its	O
faults	O
are	O
,	O
to	O
a	O
large	O
extent	O
,	O
Xerox	O
's	O
own	O
,	O
and	O
in	O
no	O
small	O
measure	O
due	O
to	O
its	O
rush	O
to	O
get	O
the	O
system	O
to	O
market	O
"	O
before	O
the	O
IBM	B-Device
PC	I-Device
.	O
</s>
<s>
The	O
reviewer	O
criticized	O
the	O
keyboard	B-Device
's	O
contact	O
bounce	O
,	O
slow	O
disk	O
access	O
,	O
and	O
"	O
pieced-together	O
...	O
minimal	O
"	O
documentation	O
,	O
and	O
warned	O
customers	O
against	O
the	O
Xerox-customized	O
WordStar	B-Application
.	O
</s>
<s>
While	O
noting	O
the	O
8	B-Device
"	I-Device
model	O
's	O
low	O
price	O
and	O
Xerox	O
's	O
strong	O
field	O
service	O
and	O
"	O
prestige	O
nameplate	O
"	O
,	O
and	O
expressing	O
hope	O
that	O
the	O
company	O
"	O
gets	O
it	O
act	O
together	O
"	O
and	O
fix	O
the	O
keyboard	B-Device
and	O
other	O
problems	O
,	O
he	O
suggested	O
that	O
potential	O
customers	O
consider	O
building	O
a	O
similar	O
computer	O
at	O
a	O
lower	O
price	O
around	O
the	O
Big	B-Device
Board	I-Device
.	O
</s>
<s>
InfoWorlds	O
reviewer	O
stated	O
that	O
he	O
and	O
his	O
colleagues	O
were	O
glad	O
when	O
Xerox	O
announced	O
the	O
820	O
,	O
because	O
"	O
at	O
last	O
a	O
recognized	O
business-equipment	O
manufacturer	O
had	O
brought	O
out	O
a	O
standard	O
CP/M	B-Application
"	O
computer	O
at	O
a	O
low	O
price	O
;	O
dealers	O
reportedly	O
were	O
also	O
pleased	O
to	O
sell	O
a	O
computer	O
from	O
a	O
well-known	O
company	O
.	O
</s>
<s>
In	O
November	O
it	O
stated	O
that	O
the	O
new	O
IBM	B-Device
PC	I-Device
was	O
much	O
more	O
attractive	O
;	O
"	O
we	O
think	O
the	O
bulk	O
of	O
the	O
sales	O
will	O
go	O
to	O
IBM	O
"	O
.	O
</s>
