<s>
Digital	O
Equipment	O
Corporation	O
(	O
DEC	O
)	O
'	O
s	O
PDP-10	B-Device
,	O
later	O
marketed	O
as	O
the	O
DECsystem-10	B-Device
,	O
is	O
a	O
mainframe	B-Architecture
computer	I-Architecture
family	O
manufactured	O
beginning	O
in	O
1966	O
and	O
discontinued	O
in	O
1983	O
.	O
</s>
<s>
1970s	O
models	O
and	O
beyond	O
were	O
marketed	O
under	O
the	O
DECsystem-10	B-Device
name	O
,	O
especially	O
as	O
the	O
TOPS-10	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
became	O
widely	O
used	O
.	O
</s>
<s>
The	O
PDP-10	B-Device
'	O
s	O
architecture	O
is	O
almost	O
identical	O
to	O
that	O
of	O
DEC	O
's	O
earlier	O
PDP-6	B-Device
,	O
sharing	O
the	O
same	O
36-bit	O
word	O
length	O
and	O
slightly	O
extending	O
the	O
instruction	B-General_Concept
set	I-General_Concept
(	O
but	O
with	O
improved	O
hardware	O
implementation	O
)	O
.	O
</s>
<s>
Some	O
aspects	O
of	O
the	O
instruction	B-General_Concept
set	I-General_Concept
are	O
unusual	O
,	O
most	O
notably	O
the	O
byte	B-Application
instructions	O
,	O
which	O
operate	O
on	O
bit	O
fields	O
of	O
any	O
size	O
from	O
1	O
to	O
36	O
bits	O
inclusive	O
,	O
according	O
to	O
the	O
general	O
definition	O
of	O
a	O
byte	B-Application
as	O
a	O
contiguous	O
sequence	O
of	O
a	O
fixed	O
number	O
of	O
bits	O
.	O
</s>
<s>
The	O
PDP-10	B-Device
was	O
found	O
in	O
many	O
university	O
computing	O
facilities	O
and	O
research	O
labs	O
during	O
the	O
1970s	O
,	O
the	O
most	O
notable	O
being	O
Harvard	O
University	O
's	O
Aiken	O
Computation	O
Laboratory	O
,	O
MIT	O
's	O
AI	O
Lab	O
and	O
Project	O
MAC	O
,	O
Stanford	O
's	O
SAIL	O
,	O
Computer	O
Center	O
Corporation	O
(	O
CCC	O
)	O
,	O
ETH	O
(	O
ZIR	O
)	O
,	O
and	O
Carnegie	O
Mellon	O
University	O
.	O
</s>
<s>
Its	B-Application
main	O
operating	B-General_Concept
systems	I-General_Concept
,	O
TOPS-10	B-Operating_System
and	O
TENEX	B-Operating_System
,	O
were	O
used	O
to	O
build	O
out	O
the	O
early	O
ARPANET	O
.	O
</s>
<s>
For	O
these	O
reasons	O
,	O
the	O
PDP-10	B-Device
looms	O
large	O
in	O
early	O
hacker	O
folklore	O
.	O
</s>
<s>
Projects	O
to	O
extend	O
the	O
PDP-10	B-Device
line	O
were	O
eclipsed	O
by	O
the	O
success	O
of	O
the	O
unrelated	O
VAX	B-Device
superminicomputer	B-Device
,	O
and	O
the	O
cancellation	O
of	O
the	O
PDP-10	B-Device
line	O
was	O
announced	O
in	O
1983	O
.	O
</s>
<s>
According	O
to	O
reports	O
,	O
DEC	O
sold	O
"	O
about	O
1500	O
DECsystem-10s	B-Device
by	O
the	O
end	O
of	O
1980.	O
"	O
</s>
<s>
The	O
original	O
PDP-10	B-Device
processor	O
is	O
the	O
KA10	O
,	O
introduced	O
in	O
1968	O
.	O
</s>
<s>
It	O
uses	O
discrete	O
transistors	B-Application
packaged	O
in	O
DEC	O
's	O
Flip-Chip	B-Device
technology	O
,	O
with	O
backplanes	O
wire	O
wrapped	O
via	O
a	O
semi-automated	O
manufacturing	O
process	O
.	O
</s>
<s>
Its	B-Application
cycle	O
time	O
is	O
1μs	O
and	O
its	B-Application
add	O
time	O
2.1μs	O
.	O
</s>
<s>
In	O
1973	O
,	O
the	O
KA10	O
was	O
replaced	O
by	O
the	O
KI10	B-Device
,	O
which	O
uses	O
transistor	B-General_Concept
–	I-General_Concept
transistor	I-General_Concept
logic	I-General_Concept
(	O
TTL	B-General_Concept
)	O
SSI	O
.	O
</s>
<s>
This	O
was	O
joined	O
in	O
1975	O
by	O
the	O
higher-performance	O
KL10	B-Device
(	O
later	O
faster	O
variants	O
)	O
,	O
which	O
is	O
built	O
from	O
emitter-coupled	B-General_Concept
logic	I-General_Concept
(	O
ECL	O
)	O
,	O
microprogrammed	O
,	O
and	O
has	O
cache	B-General_Concept
memory	O
.	O
</s>
<s>
The	O
KL10	B-Device
's	O
performance	O
was	O
about	O
1	O
megaflops	O
using	O
36-bit	O
floating	O
point	O
numbers	O
on	O
matrix	O
row	O
reduction	O
.	O
</s>
<s>
It	O
was	O
slightly	O
faster	O
than	O
the	O
newer	O
VAX-11/750	O
,	O
although	O
more	O
limited	O
in	O
memory	O
.	O
</s>
<s>
A	O
smaller	O
,	O
less	O
expensive	O
model	O
,	O
the	O
KS10	B-Device
,	O
was	O
introduced	O
in	O
1978	O
,	O
using	O
TTL	B-General_Concept
and	O
Am2901	B-General_Concept
bit-slice	B-General_Concept
components	O
and	O
including	O
the	O
PDP-11	B-Device
Unibus	B-Device
to	O
connect	O
peripherals	O
.	O
</s>
<s>
The	O
KS10	B-Device
was	O
marketed	O
as	O
the	O
DECSYSTEM-2020	O
,	O
part	O
of	O
the	O
DECSYSTEM-20	B-Device
range	O
;	O
it	O
was	O
DEC	O
's	O
entry	O
in	O
the	O
distributed	B-Architecture
processing	I-Architecture
arena	O
,	O
and	O
it	O
was	O
introduced	O
as	O
"	O
the	O
world	O
's	O
lowest	O
cost	O
mainframe	B-Architecture
computer	I-Architecture
system.	O
"	O
</s>
<s>
As	O
supplied	O
by	O
DEC	O
,	O
it	O
did	O
not	O
include	O
paging	B-Architecture
hardware	O
;	O
memory	B-General_Concept
management	I-General_Concept
consists	O
of	O
two	O
sets	O
of	O
protection	O
and	O
relocation	O
registers	O
,	O
called	O
base	B-General_Concept
and	I-General_Concept
bounds	I-General_Concept
registers	O
.	O
</s>
<s>
This	O
allows	O
each	O
half	O
of	O
a	O
user	O
's	O
address	B-General_Concept
space	I-General_Concept
to	O
be	O
limited	O
to	O
a	O
set	O
section	O
of	O
main	O
memory	O
,	O
designated	O
by	O
the	O
base	O
physical	O
address	O
and	O
size	O
.	O
</s>
<s>
This	O
allows	O
the	O
model	O
of	O
separate	O
read-only	O
shareable	O
code	O
segment	O
(	O
normally	O
the	O
high	O
segment	O
)	O
and	O
read-write	B-General_Concept
data/stack	O
segment	O
(	O
normally	O
the	O
low	O
segment	O
)	O
used	O
by	O
TOPS-10	B-Operating_System
and	O
later	O
adopted	O
by	O
Unix	B-Application
.	O
</s>
<s>
Some	O
KA10	O
machines	O
,	O
first	O
at	O
MIT	O
,	O
and	O
later	O
at	O
Bolt	O
,	O
Beranek	O
and	O
Newman	O
(	O
BBN	O
)	O
,	O
were	O
modified	O
to	O
add	O
virtual	B-Architecture
memory	I-Architecture
and	O
support	O
for	O
demand	B-General_Concept
paging	I-General_Concept
,	O
and	O
more	O
physical	O
memory	O
.	O
</s>
<s>
The	O
KI10	B-Device
introduced	O
support	O
for	O
paged	B-Architecture
memory	I-Architecture
management	O
,	O
and	O
also	O
support	O
a	O
larger	O
physical	O
address	B-General_Concept
space	I-General_Concept
of	O
4	O
megawords	O
.	O
</s>
<s>
KI10	B-Device
models	O
include	O
1060	O
,	O
1070	O
and	O
1077	O
,	O
the	O
latter	O
incorporating	O
two	O
CPUs	B-Device
.	O
</s>
<s>
The	O
original	O
KL10	B-Device
PDP-10	B-Device
(	O
also	O
marketed	O
as	O
DECsystem-10	B-Device
)	O
models	O
(	O
1080	O
,	O
1088	O
,	O
etc	O
.	O
)	O
</s>
<s>
use	O
the	O
original	O
PDP-10	B-Device
memory	O
bus	O
,	O
with	O
external	O
memory	O
modules	O
.	O
</s>
<s>
The	O
processors	O
used	O
in	O
the	O
DECSYSTEM-20	B-Device
(	O
2040	O
,	O
2050	O
,	O
2060	O
,	O
2065	O
)	O
,	O
commonly	O
but	O
incorrectly	O
called	O
"	O
KL20	O
"	O
,	O
use	O
internal	O
memory	O
,	O
mounted	O
in	O
the	O
same	O
cabinet	O
as	O
the	O
CPU	B-General_Concept
.	O
</s>
<s>
The	O
10xx	O
models	O
also	O
have	O
different	O
packaging	O
;	O
they	O
come	O
in	O
the	O
original	O
tall	O
PDP-10	B-Device
cabinets	O
,	O
rather	O
than	O
the	O
short	O
ones	O
used	O
later	O
on	O
for	O
the	O
DECSYSTEM-20	B-Device
.	O
</s>
<s>
The	O
differences	O
between	O
the	O
10xx	O
and	O
20xx	O
models	O
were	O
primarily	O
which	O
operating	B-General_Concept
system	I-General_Concept
they	O
ran	O
,	O
either	O
TOPS-10	B-Operating_System
or	O
TOPS-20	B-Operating_System
.	O
</s>
<s>
Apart	O
from	O
that	O
,	O
differences	O
are	O
more	O
cosmetic	O
than	O
real	O
;	O
some	O
10xx	O
systems	O
have	O
"	O
20-style	O
"	O
internal	O
memory	O
and	O
I/O	B-General_Concept
,	O
and	O
some	O
20xx	O
systems	O
have	O
"	O
10-style	O
"	O
external	O
memory	O
and	O
an	O
I/O	B-General_Concept
bus	O
.	O
</s>
<s>
In	O
particular	O
,	O
all	O
ARPAnet	O
TOPS-20	B-Operating_System
systems	O
had	O
an	O
I/O	B-General_Concept
bus	O
because	O
the	O
AN20	O
IMP	B-Protocol
interface	O
was	O
an	O
I/O	B-General_Concept
bus	O
device	O
.	O
</s>
<s>
Both	O
could	O
run	O
either	O
TOPS-10	B-Operating_System
or	O
TOPS-20	B-Operating_System
microcode	B-Device
and	O
thus	O
the	O
corresponding	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
later	O
Model	O
B	O
version	O
of	O
the	O
2060	O
processors	O
removes	O
the	O
256	O
kiloword	O
limit	O
on	O
the	O
virtual	O
address	B-General_Concept
space	I-General_Concept
by	O
supporting	O
up	O
to	O
32	O
"	O
sections	O
"	O
of	O
up	O
to	O
256	O
kilowords	O
each	O
,	O
along	O
with	O
substantial	O
changes	O
to	O
the	O
instruction	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
The	O
two	O
versions	O
are	O
effectively	O
different	O
CPUs	B-Device
.	O
</s>
<s>
The	O
first	O
operating	B-General_Concept
system	I-General_Concept
that	O
takes	O
advantage	O
of	O
the	O
Model	O
B	O
's	O
capabilities	O
is	O
TOPS-20	B-Operating_System
release	O
3	O
,	O
and	O
user	O
mode	O
extended	O
addressing	O
is	O
offered	O
in	O
TOPS-20	B-Operating_System
release	O
4	O
.	O
</s>
<s>
TOPS-20	B-Operating_System
versions	O
after	O
release	O
4.1	O
only	O
run	O
on	O
a	O
Model	O
B	O
.	O
</s>
<s>
TOPS-10	B-Operating_System
versions	O
7.02	O
and	O
7.03	O
also	O
use	O
extended	O
addressing	O
when	O
run	O
on	O
a	O
1090	O
(	O
or	O
1091	O
)	O
Model	O
B	O
processor	O
running	O
TOPS-20	B-Operating_System
microcode	B-Device
.	O
</s>
<s>
The	O
final	O
upgrade	O
to	O
the	O
KL10	B-Device
was	O
the	O
MCA25	O
upgrade	O
of	O
a	O
2060	O
to	O
2065	O
(	O
or	O
a	O
1091	O
to	O
1095	O
)	O
,	O
which	O
gave	O
some	O
performance	O
increases	O
for	O
programs	O
which	O
run	O
in	O
multiple	O
sections	O
.	O
</s>
<s>
The	O
I/O	B-General_Concept
architecture	O
of	O
the	O
20xx	O
series	O
KL	O
machines	O
is	O
based	O
on	O
a	O
DEC	O
bus	O
design	O
called	O
the	O
Massbus	B-Architecture
.	O
</s>
<s>
While	O
many	O
attributed	O
the	O
success	O
of	O
the	O
PDP-11	B-Device
to	O
DEC	O
's	O
decision	O
to	O
make	O
the	O
PDP-11	B-Device
Unibus	B-Device
an	O
open	O
architecture	O
,	O
DEC	O
reverted	O
to	O
prior	O
philosophy	O
with	O
the	O
KL	O
,	O
making	O
Massbus	B-Architecture
both	O
unique	O
and	O
proprietary	O
.	O
</s>
<s>
Consequently	O
,	O
there	O
were	O
no	O
aftermarket	O
peripheral	O
manufacturers	O
who	O
made	O
devices	O
for	O
the	O
Massbus	B-Architecture
,	O
and	O
DEC	O
chose	O
to	O
price	O
their	O
own	O
Massbus	B-Architecture
devices	O
,	O
notably	O
the	O
RP06	O
disk	O
drive	O
,	O
at	O
a	O
substantial	O
premium	O
above	O
comparable	O
IBM-compatible	O
devices	O
.	O
</s>
<s>
CompuServe	O
for	O
one	O
,	O
designed	O
its	B-Application
own	O
alternative	O
disk	O
controller	O
that	O
could	O
operate	O
on	O
the	O
Massbus	B-Architecture
,	O
but	O
connect	O
to	O
IBM	O
style	O
3330	O
disk	O
subsystems	O
.	O
</s>
<s>
The	O
KL	O
class	O
machines	O
have	O
a	O
PDP-11/40	B-Device
front-end	B-General_Concept
processor	I-General_Concept
for	O
system	O
start-up	O
and	O
monitoring	O
.	O
</s>
<s>
The	O
PDP-11	B-Device
is	O
booted	O
from	O
a	O
dual-ported	O
RP06	O
disk	O
drive	O
(	O
or	O
alternatively	O
from	O
an	O
8	B-Device
"	I-Device
floppy	B-Device
disk	I-Device
drive	I-Device
or	O
DECtape	O
)	O
,	O
and	O
then	O
commands	O
can	O
be	O
given	O
to	O
the	O
PDP-11	B-Device
to	O
start	O
the	O
main	O
processor	O
,	O
which	O
is	O
typically	O
booted	O
from	O
the	O
same	O
RP06	O
disk	O
drive	O
as	O
the	O
PDP-11	B-Device
.	O
</s>
<s>
The	O
PDP-11	B-Device
performs	O
watchdog	O
functions	O
once	O
the	O
main	O
processor	O
is	O
running	O
.	O
</s>
<s>
Communication	O
with	O
IBM	O
mainframes	B-Architecture
,	O
including	O
Remote	B-Protocol
Job	I-Protocol
Entry	I-Protocol
(	O
RJE	B-Protocol
)	O
,	O
was	O
accomplished	O
via	O
a	O
DN61	O
or	O
DN-64	O
front-end	B-General_Concept
processor	I-General_Concept
,	O
using	O
a	O
PDP-11/40	B-Device
or	O
PDP-11/34a	O
.	O
</s>
<s>
The	O
KS10	B-Device
is	O
a	O
lower-cost	O
PDP-10	B-Device
built	O
using	O
AMD	B-General_Concept
2901	I-General_Concept
bit-slice	B-General_Concept
chips	O
,	O
with	O
an	O
Intel	B-General_Concept
8080A	I-General_Concept
microprocessor	O
as	O
a	O
control	O
processor	O
.	O
</s>
<s>
The	O
KS10	B-Device
design	O
was	O
crippled	O
to	O
be	O
a	O
Model	O
A	O
even	O
though	O
most	O
of	O
the	O
necessary	O
data	O
paths	O
needed	O
to	O
support	O
the	O
Model	O
B	O
architecture	O
are	O
present	O
.	O
</s>
<s>
This	O
was	O
no	O
doubt	O
intended	O
to	O
segment	O
the	O
market	O
,	O
but	O
it	O
greatly	O
shortened	O
the	O
KS10	B-Device
's	O
product	O
life	O
.	O
</s>
<s>
The	O
KS	O
system	O
uses	O
a	O
similar	O
boot	O
procedure	O
to	O
the	O
KL10	B-Device
.	O
</s>
<s>
The	O
8080	B-General_Concept
control	O
processor	O
loads	O
the	O
microcode	B-Device
from	O
an	O
RM03	O
,	O
RM80	O
,	O
or	O
RP06	O
disk	O
or	O
magnetic	O
tape	O
and	O
then	O
starts	O
the	O
main	O
processor	O
.	O
</s>
<s>
The	O
8080	B-General_Concept
switches	O
modes	O
after	O
the	O
operating	B-General_Concept
system	I-General_Concept
boots	O
and	O
controls	O
the	O
console	O
and	O
remote	O
diagnostic	O
serial	O
ports	O
.	O
</s>
<s>
A	O
mix	O
of	O
up	O
to	O
eight	O
of	O
these	O
could	O
be	O
supported	O
,	O
using	O
seven-track	B-Device
or	O
nine-track	B-Device
devices	O
.	O
</s>
<s>
The	O
TU20	O
and	O
TU30	O
each	O
came	O
in	O
A	O
(	O
9-track	B-Device
)	O
and	O
B	O
(	O
7-track	O
)	O
versions	O
,	O
and	O
all	O
of	O
the	O
aforementioned	O
tape	O
drives	O
could	O
read/write	O
from/to	O
200	O
BPI	O
,	O
556	O
BPI	O
and	O
800	O
BPI	O
IBM-compatible	O
tapes	O
.	O
</s>
<s>
From	O
the	O
first	O
PDP-6s	B-Device
to	O
the	O
KL-10	B-Device
and	O
KS-10	B-Device
,	O
the	O
user-mode	O
instruction	B-General_Concept
set	I-General_Concept
architecture	I-General_Concept
is	O
largely	O
the	O
same	O
.	O
</s>
<s>
The	O
only	O
major	O
change	O
to	O
the	O
architecture	O
is	O
the	O
addition	O
of	O
multi-section	O
extended	O
addressing	O
in	O
the	O
KL-10	B-Device
;	O
extended	O
addressing	O
,	O
which	O
changes	O
the	O
process	O
of	O
generating	O
the	O
effective	O
address	O
of	O
an	O
instruction	O
,	O
is	O
briefly	O
discussed	O
at	O
the	O
end	O
.	O
</s>
<s>
+	O
DEC	B-Device
PDP-10	I-Device
registers	O
00	O
.	O
</s>
<s>
The	O
"	O
PC	O
Word	O
"	O
register	O
is	O
split	O
in	O
half	O
;	O
the	O
right	O
18-bits	O
contains	O
the	O
program	B-General_Concept
counter	I-General_Concept
and	O
the	O
left	O
13-bits	O
contains	O
the	O
processor	O
status	O
flags	O
,	O
with	O
five	O
zeros	O
between	O
the	O
two	O
sections	O
.	O
</s>
<s>
In	O
the	O
original	O
KA-10	B-Device
systems	O
,	O
these	O
registers	O
are	O
simply	O
the	O
first	O
16	O
words	O
of	O
main	O
memory	O
.	O
</s>
<s>
The	O
"	O
fast	O
registers	O
"	O
hardware	O
option	O
implements	O
them	O
as	O
registers	O
in	O
the	O
CPU	B-General_Concept
,	O
still	O
addressable	O
as	O
the	O
first	O
16	O
words	O
of	O
memory	O
.	O
</s>
<s>
Some	O
software	O
takes	O
advantage	O
of	O
this	O
by	O
using	O
the	O
registers	O
as	O
an	O
instruction	B-General_Concept
cache	I-General_Concept
by	O
loading	O
code	O
into	O
the	O
registers	O
and	O
then	O
jumping	O
to	O
the	O
appropriate	O
address	O
;	O
this	O
is	O
used	O
,	O
for	O
example	O
,	O
in	O
Maclisp	B-Language
to	O
implement	O
one	O
version	O
of	O
the	O
garbage	B-General_Concept
collector	I-General_Concept
.	O
</s>
<s>
Later	O
models	O
all	O
have	O
registers	O
in	O
the	O
CPU	B-General_Concept
.	O
</s>
<s>
Besides	O
the	O
difference	O
in	O
memory	O
referencing	O
described	O
above	O
,	O
supervisor-mode	O
programs	O
can	O
execute	O
input/output	B-General_Concept
operations	O
.	O
</s>
<s>
The	O
major	O
datatypes	O
which	O
are	O
directly	O
supported	O
by	O
the	O
architecture	O
are	O
two	B-General_Concept
's	I-General_Concept
complement	I-General_Concept
36-bit	O
integer	O
arithmetic	O
(	O
including	O
bitwise	O
operations	O
)	O
,	O
36-bit	O
floating-point	O
,	O
and	O
halfwords	O
.	O
</s>
<s>
Byte	B-Application
pointers	O
are	O
supported	O
by	O
special	O
instructions	O
.	O
</s>
<s>
A	O
word	O
structured	O
as	O
a	O
"	O
count	O
"	O
half	O
and	O
a	O
"	O
pointer	O
"	O
half	O
facilitates	O
the	O
use	O
of	O
bounded	O
regions	O
of	O
memory	O
,	O
notably	O
stacks	B-General_Concept
.	O
</s>
<s>
+	O
DEC	B-Device
PDP-10	I-Device
instruction	O
formats	O
00	O
01	O
02	O
03	O
04	O
05	O
06	O
07	O
08	O
09	O
10	O
11	O
12	O
13	O
14	O
15	O
16	O
17	O
18	O
.	O
</s>
<s>
There	O
are	O
two	O
formats	O
,	O
general	O
instructions	O
and	O
input/output	B-General_Concept
instructions	O
.	O
</s>
<s>
In	O
general	O
instructions	O
,	O
the	O
leftmost	O
9	O
bits	O
,	O
0	O
to	O
8	O
,	O
contain	O
an	O
instruction	B-Language
opcode	I-Language
.	O
</s>
<s>
Many	O
of	O
the	O
possible	O
512	O
codes	O
are	O
not	O
defined	O
in	O
the	O
base	O
model	O
machines	O
and	O
are	O
reserved	O
for	O
expansion	O
like	O
the	O
addition	O
of	O
a	O
hardware	O
floating	B-General_Concept
point	I-General_Concept
unit	I-General_Concept
.	O
</s>
<s>
Following	O
the	O
opcode	B-Language
in	O
bits	O
9	O
to	O
12	O
is	O
the	O
number	O
of	O
a	O
register	O
which	O
will	O
be	O
used	O
for	O
the	O
instruction	O
.	O
</s>
<s>
The	O
input/output	B-General_Concept
instructions	O
all	O
start	O
with	O
bits	O
0	O
through	O
3	O
being	O
set	O
to	O
1	O
(	O
decimal	O
value	O
7	O
)	O
,	O
bits	O
3	O
through	O
9	O
containing	O
a	O
device	O
number	O
,	O
and	O
10	O
through	O
12	O
the	O
instruction	B-Language
opcode	I-Language
.	O
</s>
<s>
Later	O
architectures	O
have	O
paged	B-Architecture
memory	I-Architecture
access	O
,	O
allowing	O
non-contiguous	O
address	B-General_Concept
spaces	I-General_Concept
.	O
</s>
<s>
The	O
CPU	B-General_Concept
's	O
general-purpose	O
registers	O
can	O
also	O
be	O
addressed	O
as	O
memory	O
locations	O
0	O
–	O
15	O
.	O
</s>
<s>
The	O
mnemonics	O
for	O
these	O
instructions	O
all	O
start	O
with	O
JUMP	O
,	O
JUMPA	O
meaning	O
"	O
jump	O
always	O
"	O
and	O
JUMP	O
meaning	O
"	O
jump	O
never	O
"	O
–	O
as	O
a	O
consequence	O
of	O
the	O
symmetric	O
design	O
of	O
the	O
instruction	B-General_Concept
set	I-General_Concept
,	O
it	O
contains	O
several	O
no-ops	O
such	O
as	O
JUMP	O
.	O
</s>
<s>
On	O
the	O
KA10	O
and	O
KI10	B-Device
,	O
JRST	O
is	O
faster	O
than	O
JUMPA	O
,	O
so	O
the	O
standard	O
unconditional	O
jump	O
is	O
JRST	O
.	O
</s>
<s>
The	O
conditional	O
skip	O
operations	O
compare	O
register	O
and	O
memory	O
contents	O
and	O
skip	O
the	O
next	B-General_Concept
instruction	I-General_Concept
(	O
which	O
is	O
often	O
an	O
unconditional	O
jump	O
)	O
depending	O
on	O
the	O
result	O
of	O
the	O
comparison	O
.	O
</s>
<s>
A	O
simple	O
example	O
is	O
CAMN	O
A	O
,	O
LOC	O
which	O
compares	O
the	O
contents	O
of	O
register	O
A	O
with	O
the	O
contents	O
of	O
location	O
LOC	O
and	O
skips	O
the	O
next	B-General_Concept
instruction	I-General_Concept
if	O
they	O
are	O
not	O
equal	O
.	O
</s>
<s>
If	O
all	O
those	O
bits	O
are	O
Equal	O
to	O
zero	O
,	O
skip	O
the	O
next	B-General_Concept
instruction	I-General_Concept
;	O
and	O
in	O
any	O
case	O
,	O
replace	O
those	O
bits	O
by	O
their	O
boolean	O
complement	O
.	O
</s>
<s>
Particularly	O
notable	O
are	O
the	O
stack	B-Application
instructions	O
PUSH	B-Application
and	I-Application
POP	I-Application
,	O
and	O
the	O
corresponding	O
stack	B-Application
call	O
instructions	O
PUSHJ	O
and	O
POPJ	O
.	O
</s>
<s>
The	O
byte	B-Application
instructions	O
use	O
a	O
special	O
format	O
of	O
indirect	O
word	O
to	O
extract	O
and	O
store	O
arbitrary-sized	O
bit	O
fields	O
,	O
possibly	O
advancing	O
a	O
pointer	O
to	O
the	O
next	O
unit	O
.	O
</s>
<s>
The	O
PDP-10	B-Device
does	O
not	O
use	O
memory-mapped	O
devices	O
,	O
in	O
contrast	O
to	O
the	O
PDP-11	B-Device
and	O
later	O
DEC	O
machines	O
.	O
</s>
<s>
Finally	O
,	O
it	O
checks	O
the	O
counter	O
side	O
of	O
the	O
value	O
at	O
E	O
,	O
if	O
it	O
is	O
non-zero	O
,	O
it	O
skips	O
the	O
next	B-General_Concept
instruction	I-General_Concept
.	O
</s>
<s>
If	O
it	O
is	O
zero	O
,	O
it	O
performs	O
the	O
next	B-General_Concept
instruction	I-General_Concept
,	O
normally	O
a	O
JUMP	O
back	O
to	O
the	O
top	O
of	O
the	O
loop	O
.	O
</s>
<s>
The	O
final	O
set	O
of	O
I/O	B-General_Concept
instructions	O
are	O
used	O
to	O
write	O
and	O
read	O
condition	O
codes	O
on	O
the	O
device	O
,	O
CONO	O
and	O
CONI	O
.	O
</s>
<s>
Additionally	O
,	O
CONSZ	O
will	O
perform	O
a	O
CONI	O
,	O
bitmask	O
the	O
retrieved	O
data	O
against	O
the	O
value	O
in	O
E	O
,	O
and	O
then	O
skip	O
the	O
next	B-General_Concept
instruction	I-General_Concept
if	O
it	O
is	O
zero	O
,	O
used	O
in	O
a	O
fashion	O
similar	O
to	O
the	O
BLK	O
commands	O
.	O
</s>
<s>
A	O
second	O
use	O
of	O
the	O
CONO	O
instruction	O
is	O
to	O
set	O
the	O
device	O
's	O
priority	O
level	O
for	O
interrupt	B-Application
handling	I-Application
.	O
</s>
<s>
Level	O
1	O
is	O
the	O
highest	O
,	O
meaning	O
that	O
if	O
two	O
devices	O
raise	O
an	O
interrupt	B-Application
at	O
the	O
same	O
time	O
,	O
the	O
lowest-numbered	O
device	O
will	O
begin	O
processing	O
.	O
</s>
<s>
Level	O
0	O
means	O
"	O
no	O
interrupts	B-Application
"	O
,	O
so	O
a	O
device	O
set	O
to	O
level	O
0	O
will	O
not	O
stop	O
the	O
processor	O
even	O
if	O
it	O
does	O
raise	O
an	O
interrupt	B-Application
.	O
</s>
<s>
When	O
the	O
interrupt	B-Application
is	O
received	O
and	O
accepted	O
,	O
meaning	O
no	O
higher-priority	O
interrupt	B-Application
is	O
already	O
running	O
,	O
the	O
system	O
stops	O
at	O
the	O
next	O
memory	O
read	O
part	O
of	O
the	O
instruction	B-General_Concept
cycle	I-General_Concept
and	O
instead	O
begins	O
processing	O
at	O
the	O
address	O
stored	O
in	O
the	O
first	O
of	O
those	O
two	O
locations	O
.	O
</s>
<s>
It	O
is	O
up	O
to	O
the	O
interrupt	B-General_Concept
handler	I-General_Concept
to	O
turn	O
off	O
the	O
interrupt	B-Application
level	O
when	O
it	O
is	O
complete	O
,	O
which	O
it	O
can	O
do	O
by	O
running	O
a	O
CONO	O
,	O
DATA	O
or	O
BLK	O
instruction	O
.	O
</s>
<s>
Device	O
4	O
is	O
the	O
"	O
priority	O
interrupt	B-Application
"	O
,	O
which	O
can	O
be	O
read	O
using	O
CONI	O
to	O
gain	O
additional	O
information	O
about	O
an	O
interrupt	B-Application
that	O
has	O
occurred	O
.	O
</s>
<s>
In	O
processors	O
supporting	O
extended	O
addressing	O
,	O
the	O
address	B-General_Concept
space	I-General_Concept
is	O
divided	O
into	O
"	O
sections	O
"	O
.	O
</s>
<s>
An	O
indirect	O
word	O
can	O
either	O
be	O
a	O
"	O
local	O
indirect	O
word	O
"	O
,	O
with	O
its	B-Application
uppermost	O
bit	O
set	O
,	O
the	O
next	O
12	O
bits	O
reserved	O
,	O
and	O
the	O
remaining	O
bits	O
being	O
an	O
indirect	O
bit	O
,	O
a	O
4-bit	O
register	O
code	O
,	O
and	O
an	O
18-bit	O
displacement	O
,	O
or	O
a	O
"	O
global	O
indirect	O
word	O
"	O
,	O
with	O
its	B-Application
uppermost	O
bit	O
clear	O
,	O
the	O
next	O
bit	O
being	O
an	O
indirect	O
bit	O
,	O
the	O
next	O
4	O
bits	O
being	O
a	O
register	O
code	O
,	O
and	O
the	O
remaining	O
30	O
bits	O
being	O
a	O
displacement	O
.	O
</s>
<s>
The	O
original	O
PDP-10	B-Device
operating	B-General_Concept
system	I-General_Concept
was	O
simply	O
called	O
"	O
Monitor	O
"	O
,	O
but	O
was	O
later	O
renamed	O
TOPS-10	B-Operating_System
.	O
</s>
<s>
Eventually	O
the	O
PDP-10	B-Device
system	O
itself	O
was	O
renamed	O
the	O
DECsystem-10	B-Device
.	O
</s>
<s>
Early	O
versions	O
of	O
Monitor	O
and	O
TOPS-10	B-Operating_System
formed	O
the	O
basis	O
of	O
Stanford	O
's	O
WAITS	B-Application
operating	B-General_Concept
system	I-General_Concept
and	O
the	O
CompuServe	O
time-sharing	O
system	O
.	O
</s>
<s>
Over	O
time	O
,	O
some	O
PDP-10	B-Device
operators	O
began	O
running	O
operating	B-General_Concept
systems	I-General_Concept
assembled	O
from	O
major	O
components	O
developed	O
outside	O
DEC	O
.	O
For	O
example	O
,	O
the	O
main	O
Scheduler	O
might	O
come	O
from	O
one	O
university	O
,	O
the	O
Disk	O
Service	O
from	O
another	O
,	O
and	O
so	O
on	O
.	O
</s>
<s>
The	O
commercial	O
timesharing	O
services	O
such	O
as	O
CompuServe	O
,	O
On-Line	O
Systems	O
,	O
Inc	O
.	O
(	O
OLS	O
)	O
,	O
and	O
Rapidata	O
maintained	O
sophisticated	O
inhouse	O
systems	O
programming	O
groups	O
so	O
that	O
they	O
could	O
modify	O
the	O
operating	B-General_Concept
system	I-General_Concept
as	O
needed	O
for	O
their	O
own	O
businesses	O
without	O
being	O
dependent	O
on	O
DEC	O
or	O
others	O
.	O
</s>
<s>
BBN	O
developed	O
their	O
own	O
alternative	O
operating	B-General_Concept
system	I-General_Concept
,	O
TENEX	B-Operating_System
,	O
which	O
fairly	O
quickly	O
became	O
popular	O
in	O
the	O
research	O
community	O
.	O
</s>
<s>
DEC	O
later	O
ported	O
TENEX	B-Operating_System
to	O
the	O
KL10	B-Device
,	O
enhanced	O
it	O
considerably	O
,	O
and	O
named	O
it	O
TOPS-20	B-Operating_System
,	O
forming	O
the	O
DECSYSTEM-20	B-Device
line	O
.	O
</s>
<s>
MIT	O
,	O
which	O
had	O
developed	O
CTSS	O
,	O
Compatible	B-Operating_System
Time-Sharing	I-Operating_System
System	I-Operating_System
to	O
run	O
on	O
their	O
IBM	B-Device
709	I-Device
(	O
and	O
later	O
a	O
modified	O
IBM	B-Device
7094	I-Device
system	O
)	O
,	O
also	O
developed	O
ITS	B-Application
,	O
Incompatible	B-Application
Timesharing	I-Application
System	I-Application
to	O
run	O
on	O
their	O
PDP-6	B-Device
(	O
and	O
later	O
a	O
modified	O
PDP-10	B-Device
)	O
;	O
the	O
naming	O
was	O
related	O
,	O
since	O
the	O
IBM	O
and	O
the	O
DEC/PDP	O
hardware	O
were	O
different	O
,	O
i.e.	O
</s>
<s>
"	O
incompatible	O
"	O
(	O
despite	O
each	O
having	O
a	O
36-bit	O
CPU	B-General_Concept
)	O
.	O
</s>
<s>
The	O
ITS	B-Application
name	O
,	O
selected	O
by	O
Tom	O
Knight	O
,	O
"	O
was	O
a	O
play	O
on	O
"	O
the	O
CTSS	O
name	O
.	O
</s>
<s>
Tymshare	O
developed	O
TYMCOM-X	O
,	O
derived	O
from	O
TOPS-10	B-Operating_System
but	O
using	O
a	O
page-based	O
file	O
system	O
like	O
TOPS-20	B-Operating_System
.	O
</s>
<s>
In	O
1971	O
to	O
1972	O
,	O
researchers	O
at	O
Xerox	O
PARC	O
were	O
frustrated	O
by	O
top	O
company	O
management	O
's	O
refusal	O
to	O
let	O
them	O
buy	O
a	O
PDP-10	B-Device
.	O
</s>
<s>
Instead	O
,	O
a	O
group	O
led	O
by	O
Charles	O
P	O
.	O
Thacker	O
designed	O
and	O
constructed	O
two	O
PDP-10	B-Device
clone	O
systems	O
named	O
MAXC	O
(	O
pronounced	O
as	O
Max	O
,	O
in	O
honour	O
of	O
Max	O
Palevsky	O
,	O
who	O
had	O
sold	O
SDS	O
to	O
Xerox	O
)	O
for	O
their	O
own	O
use	O
.	O
</s>
<s>
MAXC	O
ran	O
a	O
modified	O
version	O
of	O
TENEX	B-Operating_System
.	O
</s>
<s>
Third-party	O
attempts	O
to	O
sell	O
PDP-10	B-Device
clones	O
were	O
relatively	O
unsuccessful	O
;	O
see	O
Foonly	O
,	O
Systems	O
Concepts	O
,	O
and	O
XKL	O
.	O
</s>
<s>
One	O
of	O
the	O
largest	O
collections	O
of	O
DECsystem-10	B-Device
architecture	O
systems	O
ever	O
assembled	O
was	O
at	O
CompuServe	O
,	O
which	O
,	O
at	O
its	B-Application
peak	O
,	O
operated	O
over	O
200	O
loosely	O
coupled	O
systems	O
in	O
three	O
data	O
centers	O
in	O
Columbus	O
,	O
Ohio	O
.	O
</s>
<s>
While	O
the	O
first	O
such	O
systems	O
were	O
bought	O
from	O
DEC	O
,	O
when	O
DEC	O
abandoned	O
the	O
PDP-10	B-Device
architecture	O
in	O
favor	O
of	O
the	O
VAX	B-Device
,	O
CompuServe	O
and	O
other	O
PDP-10	B-Device
customers	O
began	O
buying	O
plug	B-Device
compatible	I-Device
computers	O
from	O
Systems	O
Concepts	O
.	O
</s>
<s>
,	O
CompuServe	O
was	O
operating	O
a	O
small	O
number	O
of	O
PDP-10	B-Device
architecture	O
machines	O
to	O
perform	O
some	O
billing	O
and	O
routing	O
functions	O
.	O
</s>
<s>
CompuServe	O
offered	O
to	O
license	O
the	O
design	O
for	O
its	B-Application
KL	O
supply	O
to	O
DEC	O
for	O
free	O
if	O
DEC	O
would	O
promise	O
that	O
any	O
new	O
KL	O
bought	O
by	O
CompuServe	O
would	O
have	O
the	O
more	O
efficient	O
supply	O
installed	O
.	O
</s>
<s>
Another	O
modification	O
made	O
to	O
the	O
PDP-10	B-Device
by	O
CompuServe	O
engineers	O
was	O
replacing	O
the	O
hundreds	O
of	O
incandescent	O
indicator	O
lamps	O
on	O
the	O
KI10	B-Device
processor	O
cabinet	O
with	O
LED	O
lamp	O
modules	O
.	O
</s>
<s>
The	O
picture	O
on	O
the	O
right	O
hand	O
side	O
shows	O
the	O
light	O
panel	O
of	O
the	O
MF10	O
memory	O
which	O
is	O
contemporary	O
with	O
the	O
KI10	B-Device
CPU	B-General_Concept
.	O
</s>
<s>
The	O
PDP-10	B-Device
was	O
eventually	O
eclipsed	O
by	O
the	O
VAX	B-Device
superminicomputer	B-Device
machines	O
(	O
descendants	O
of	O
the	O
PDP-11	B-Device
)	O
when	O
DEC	O
recognized	O
that	O
the	O
PDP-10	B-Device
and	O
VAX	B-Device
product	O
lines	O
were	O
competing	O
with	O
each	O
other	O
and	O
decided	O
to	O
concentrate	O
its	B-Application
software	O
development	O
effort	O
on	O
the	O
more	O
profitable	O
VAX	B-Device
.	O
</s>
<s>
The	O
PDP-10	B-Device
product	O
line	O
cancellation	O
was	O
announced	O
in	O
1983	O
,	O
including	O
cancelling	O
the	O
ongoing	O
Jupiter	B-Device
project	I-Device
to	O
produce	O
a	O
new	O
high-end	O
PDP-10	B-Device
processor	O
(	O
despite	O
that	O
project	O
being	O
in	O
good	O
shape	O
at	O
the	O
time	O
of	O
the	O
cancellation	O
)	O
and	O
the	O
Minnow	O
project	O
to	O
produce	O
a	O
desktop	O
PDP-10	B-Device
,	O
which	O
may	O
then	O
have	O
been	O
at	O
the	O
prototyping	O
stage	O
.	O
</s>
<s>
This	O
event	O
spelled	O
the	O
doom	O
of	O
ITS	B-Application
and	O
the	O
technical	O
cultures	O
that	O
had	O
spawned	O
the	O
original	O
jargon	O
file	O
,	O
but	O
by	O
the	O
1990s	O
it	O
had	O
become	O
something	O
of	O
a	O
badge	O
of	O
honor	O
among	O
old-time	O
hackers	O
to	O
have	O
cut	O
one	O
's	O
teeth	O
on	O
a	O
PDP-10	B-Device
.	O
</s>
<s>
The	O
PDP-10	B-Device
assembly	B-Language
language	I-Language
instructions	O
LDB	O
and	O
DPB	O
(	O
load/deposit	O
byte	B-Application
)	O
live	O
on	O
as	O
functions	O
in	O
the	O
programming	O
language	O
Common	B-Language
Lisp	I-Language
.	O
</s>
<s>
The	O
36-bit	O
word	O
size	O
of	O
the	O
PDP-6	B-Device
and	O
PDP-10	B-Device
was	O
influenced	O
by	O
the	O
programming	O
convenience	O
of	O
having	O
2	O
LISP	O
pointers	O
,	O
each	O
18	O
bits	O
,	O
in	O
one	O
word	O
.	O
</s>
<s>
Will	O
Crowther	O
created	O
Adventure	B-Application
,	O
the	O
prototypical	O
computer	O
adventure	B-Application
game	O
,	O
for	O
a	O
PDP-10	B-Device
.	O
</s>
<s>
Don	O
Daglow	O
created	O
the	O
first	O
computer	O
baseball	B-Application
game	O
(	O
1971	O
)	O
and	O
Dungeon	B-Application
(	O
1975	O
)	O
,	O
the	O
first	O
role-playing	O
video	O
game	O
on	O
a	O
PDP-10	B-Device
.	O
</s>
<s>
Walter	O
Bright	O
originally	O
created	O
Empire	B-Application
for	O
the	O
PDP-10	B-Device
.	O
</s>
<s>
Roy	B-Protocol
Trubshaw	I-Protocol
and	O
Richard	O
Bartle	O
created	O
the	O
first	O
MUD	B-Application
on	O
a	O
PDP-10	B-Device
.	O
</s>
<s>
Zork	B-Application
was	O
written	O
on	O
the	O
PDP-10	B-Device
.	O
</s>
<s>
Infocom	O
used	O
PDP-10s	B-Device
for	O
game	O
development	O
and	O
testing	O
.	O
</s>
<s>
Bill	O
Gates	O
and	O
Paul	O
Allen	O
originally	O
wrote	O
Altair	B-Language
BASIC	I-Language
using	O
an	O
Intel	B-General_Concept
8080	I-General_Concept
simulator	O
running	O
on	O
a	O
PDP-10	B-Device
at	O
Harvard	O
University	O
.	O
</s>
<s>
Allen	O
repurposed	O
the	O
PDP-10	B-Device
assembler	B-Language
as	O
a	O
cross	B-Language
assembler	I-Language
for	O
the	O
8080	B-General_Concept
chip	O
.	O
</s>
<s>
The	O
software	O
for	O
simulation	O
of	O
historical	O
computers	O
,	O
SIMH	B-Application
,	O
contains	O
modules	O
to	O
emulate	O
all	O
the	O
PDP-10	B-Device
CPU	B-General_Concept
models	O
on	O
a	O
Windows	O
or	O
Unix-based	O
machine	O
.	O
</s>
<s>
Copies	O
of	O
DEC	O
's	O
original	O
distribution	O
tapes	O
are	O
available	O
as	O
downloads	O
from	O
the	O
Internet	O
so	O
that	O
a	O
running	O
TOPS-10	B-Operating_System
or	O
TOPS-20	B-Operating_System
system	O
may	O
be	O
established	O
.	O
</s>
<s>
ITS	B-Application
and	O
WAITS	B-Application
are	O
also	O
available	O
for	O
SIMH	B-Application
.	O
</s>
<s>
Ken	O
Harrenstien	O
's	O
KLH10	O
software	O
for	O
Unix-like	O
systems	O
emulates	O
a	O
KL10B	O
processor	O
with	O
extended	O
addressing	O
and	O
4	O
MW	O
of	O
memory	O
or	O
a	O
KS10	B-Device
processor	O
with	O
512	O
KW	O
of	O
memory	O
.	O
</s>
<s>
The	O
KL10	B-Device
emulation	O
supports	O
v.442	O
of	O
the	O
KL10	B-Device
microcode	B-Device
,	O
which	O
enables	O
it	O
to	O
run	O
the	O
final	O
versions	O
of	O
both	O
TOPS-10	B-Operating_System
and	O
TOPS-20	B-Operating_System
.	O
</s>
<s>
The	O
KS10	B-Device
emulation	O
supports	O
both	O
ITS	B-Application
v.262	O
microcode	B-Device
for	O
the	O
final	O
version	O
of	O
KS10	B-Device
ITS	B-Application
and	O
DEC	O
v.130	O
microcode	B-Device
for	O
the	O
final	O
versions	O
of	O
KS	O
TOPS-10	B-Operating_System
and	O
TOPS-20	B-Operating_System
.	O
</s>
