<s>
OS/8	B-Operating_System
is	O
the	O
primary	O
operating	B-General_Concept
system	I-General_Concept
used	O
on	O
the	O
Digital	O
Equipment	O
Corporation	O
's	O
PDP-8	B-Device
minicomputer	B-Architecture
.	O
</s>
<s>
PDP-8	B-Device
operating	B-General_Concept
systems	I-General_Concept
which	O
precede	O
OS/8	B-Operating_System
include	O
:	O
</s>
<s>
R-L	O
Monitor	O
,	O
also	O
referred	O
to	O
as	O
MS/8	B-Application
.	O
</s>
<s>
This	O
is	O
what	O
became	O
OS/8	B-Operating_System
in	O
1971	O
.	O
</s>
<s>
Other/related	O
DEC	O
operating	B-General_Concept
systems	I-General_Concept
are	O
OS/78	B-Device
,	O
OS/278	O
,	O
and	O
OS/12	O
.	O
</s>
<s>
The	O
latter	O
is	O
a	O
virtually	O
identical	O
version	O
of	O
OS/8	B-Operating_System
,	O
and	O
runs	O
on	O
Digital	O
's	O
PDP-12	B-Device
computer	O
.	O
</s>
<s>
Digital	O
released	O
OS/8	B-Operating_System
images	O
for	O
non-commercial	O
purposes	O
which	O
can	O
be	O
emulated	O
through	O
SIMH	B-Application
.	O
</s>
<s>
OS/8	B-Operating_System
provides	O
a	O
simple	O
operating	O
environment	O
that	O
is	O
commensurate	O
in	O
complexity	O
and	O
scale	O
with	O
the	O
PDP-8	B-Device
computers	O
on	O
which	O
it	O
ran	O
.	O
</s>
<s>
The	O
device	B-Application
drivers	I-Application
have	O
to	O
be	O
cleverly	O
written	O
as	O
they	O
can	O
occupy	O
only	O
one	O
or	O
two	O
memory	O
pages	O
of	O
128	O
12-bit	B-Device
words	O
,	O
and	O
have	O
to	O
be	O
able	O
to	O
run	O
in	O
any	O
page	O
in	O
field	O
0	O
.	O
</s>
<s>
The	O
memory-resident	O
"	O
footprint	O
"	O
of	O
OS/8	B-Operating_System
is	O
only	O
256	O
words	O
;	O
128	O
words	O
at	O
the	O
top	O
of	O
Field	O
0	O
and	O
128	O
words	O
at	O
the	O
top	O
of	O
Field	O
1	O
.	O
</s>
<s>
The	O
rest	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
(	O
the	O
USR	O
,	O
"	O
User	O
Service	O
Routines	O
"	O
)	O
swaps	O
in	O
and	O
out	O
of	O
memory	O
transparently	O
(	O
with	O
regard	O
to	O
the	O
user	O
's	O
program	O
)	O
as	O
needed	O
.	O
</s>
<s>
Early	O
versions	O
of	O
OS/8	B-Operating_System
have	O
a	O
very	O
rudimentary	O
command-line	B-Application
interpreter	O
with	O
very	O
few	O
basic	O
commands	B-Application
:	O
,	O
,	O
,	O
,	O
,	O
and	O
.	O
</s>
<s>
With	O
version	O
3	O
they	O
add	O
a	O
more	O
sophisticated	O
overlay	O
called	O
CCL	B-Operating_System
(	O
Concise	B-Operating_System
Command	I-Operating_System
Language	I-Operating_System
)	O
that	O
implements	O
many	O
more	O
commands	B-Application
.	O
</s>
<s>
OS/8	B-Operating_System
'	O
s	O
CCL	B-Operating_System
is	O
directly	O
patterned	O
after	O
the	O
CCL	B-Operating_System
found	O
on	O
Digital	O
's	O
PDP-10	B-Device
systems	O
running	O
TOPS-10	B-Operating_System
.	O
</s>
<s>
In	O
fact	O
,	O
much	O
of	O
the	O
OS/8	B-Operating_System
software	O
system	O
is	O
deliberately	O
designed	O
to	O
mimic	O
,	O
as	O
closely	O
as	O
possible	O
,	O
the	O
TOPS-10	B-Operating_System
operating	O
environment	O
.	O
</s>
<s>
(	O
The	O
CCL	B-Operating_System
command	O
language	O
is	O
used	O
on	O
PDP-11	B-Device
computers	O
running	O
RT-11	B-Operating_System
,	O
RSX-11	B-Application
,	O
and	O
RSTS/E	B-Operating_System
,	O
providing	O
a	O
similar	O
user	O
operating	O
environment	O
across	O
all	O
three	O
architectures	O
:	O
PDP-8s	B-Device
,	O
PDP-10s	B-Device
,	O
and	O
PDP-11s	B-Device
.	O
)	O
</s>
<s>
The	O
basic	O
OS	O
and	O
CCL	B-Operating_System
implements	O
many	O
rather	O
sophisticated	O
commands	B-Application
,	O
many	O
of	O
which	O
still	O
do	O
not	O
exist	O
in	O
modern	O
command	O
languages	O
,	O
not	O
even	O
in	O
MS-DOS	B-Application
,	O
Windows	B-Application
,	O
or	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
The	O
and	O
commands	B-Application
permit	O
the	O
use	O
of	O
logical	O
device	O
names	O
in	O
a	O
program	O
instead	O
of	O
physical	O
names	O
(	O
as	O
required	O
in	O
MS-DOS	B-Application
)	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
program	O
can	O
write	O
to	O
device	O
,	O
and	O
with	O
an	O
initial	O
""	O
then	O
the	O
file	O
is	O
created	O
on	O
physical	O
device	O
RXA2	O
(	O
the	O
second	O
floppy	B-Device
disk	I-Device
drive	I-Device
)	O
.	O
</s>
<s>
VAX/VMS	B-Operating_System
and	O
the	O
Amiga	B-Device
's	O
operating	B-General_Concept
system	I-General_Concept
AmigaOS	B-Application
(	O
and	O
other	O
OSes	O
built	O
around	O
TRIPOS	B-Operating_System
)	O
make	O
considerable	O
use	O
of	O
this	O
feature	O
.	O
</s>
<s>
One	O
of	O
them	O
,	O
a	O
command	O
under	O
OS-78	O
,	O
is	O
,	O
which	O
re-enables	O
the	O
MONITOR	O
commands	B-Application
that	O
are	O
not	O
part	O
of	O
OS-78	O
.	O
</s>
<s>
The	O
command	O
can	O
reconfigure	O
the	O
OS	O
on	O
the	O
fly	O
,	O
even	O
adding	O
device	B-Application
drivers	I-Application
,	O
often	O
without	O
having	O
to	O
reboot	O
the	O
OS	O
.	O
</s>
<s>
The	O
OS	O
can	O
boot	O
from	O
a	O
hard	O
disk	B-Device
and	O
present	O
the	O
command	O
prompt	O
in	O
under	O
half	O
a	O
second	O
.	O
</s>
<s>
OS/8	B-Operating_System
supports	O
a	O
simple	O
,	O
flat	O
file	B-Application
system	I-Application
on	O
a	O
variety	O
of	O
mass	B-Device
storage	I-Device
devices	I-Device
including	O
:	O
</s>
<s>
Filenames	B-Operating_System
on	O
the	O
PDP-8	B-Device
take	O
the	O
form	O
of	O
where	O
"	O
F	O
"	O
represents	O
an	O
uppercase	O
,	O
alphanumeric	O
character	O
of	O
the	O
filename	O
and	O
"	O
X	O
"	O
represents	O
an	O
uppercase	O
,	O
alphanumeric	O
character	O
of	O
the	O
extension	O
(	O
filetype	O
)	O
.	O
</s>
<s>
PIP	B-Application
includes	O
an	O
option	O
to	O
compress	O
(	O
"	O
squeeze	O
"	O
)	O
the	O
filesystem	B-Application
,	O
so	O
that	O
all	O
unallocated	O
space	O
is	O
moved	O
to	O
a	O
single	O
extent	O
at	O
the	O
end	O
of	O
the	O
disk	B-Device
.	O
</s>
<s>
This	O
can	O
be	O
invoked	O
by	O
the	O
SQuish	O
CCL	B-Operating_System
command	O
,	O
much	O
as	O
MUNG	O
can	O
be	O
used	O
to	O
run	O
a	O
TECO	B-Application
macro	O
.	O
</s>
<s>
OS/8	B-Operating_System
volumes	O
have	O
a	O
limited	O
maximum	O
storage	O
size	O
(	O
4096	O
blocks	O
of	O
256	O
twelve-bit	O
words	O
)	O
and	O
the	O
RK05	O
(	O
2.4MB	O
)	O
moving-head	O
disk	B-Device
exceeds	O
this	O
size	O
:	O
"	O
1.6	O
million	O
words	O
of	O
storage	O
"	O
.	O
</s>
<s>
ASCII	O
files	O
are	O
stored	O
as	O
three	O
8-bit	O
characters	O
per	O
pair	O
of	O
12-bit	B-Device
words	O
.	O
</s>
<s>
OS/8	B-Operating_System
allocates	O
the	O
PDP-8	B-Device
'	O
s	O
12	B-Device
bit	I-Device
words	O
for	O
storing	O
dates	O
per	O
:	O
</s>
<s>
The	O
insufficiency	O
of	O
a	O
three-bit	O
year	O
field	O
,	O
capable	O
of	O
storing	O
only	O
eight	O
years	O
,	O
was	O
recognized	O
when	O
COS-310	B-Operating_System
was	O
developed	O
.	O
</s>
<s>
The	O
CUSPs	O
(	O
Commonly-Used	O
System	O
Programs	O
,	O
that	O
is	O
utilities	O
)	O
supplied	O
with	O
OS/8	B-Operating_System
include	O
:	O
</s>
<s>
MACREL	O
(	O
A	O
relocating	O
assembler	B-Language
that	O
,	O
unlike	O
PAL	O
,	O
implements	O
macros	O
.	O
</s>
<s>
FORTRAN-II	O
.	O
</s>
<s>
TECO	B-Application
(	O
Text	B-Application
Editor	I-Application
and	I-Application
COrrector	I-Application
,	O
a	O
sophisticated	O
editor	O
)	O
.	O
</s>
<s>
The	O
MUNG	O
command	O
runs	O
TECO	B-Application
macros	O
.	O
</s>
<s>
CCL	B-Operating_System
,	O
the	O
command	B-Application
line	I-Application
interpreter	O
,	O
supplied	O
in	O
source	O
form	O
and	O
user-extensible	O
.	O
</s>
<s>
The	O
single-user	O
BASIC	O
uses	O
several	O
overlays	O
to	O
provide	O
the	O
full	O
functionality	O
of	O
the	O
language	O
;	O
when	O
OS/8	B-Operating_System
is	O
booted	O
from	O
a	O
DECtape	O
,	O
a	O
noticeable	O
delay	O
occurred	O
each	O
time	O
BASIC	O
is	O
required	O
to	O
switch	O
overlays	O
as	O
they	O
need	O
to	O
be	O
read	O
from	O
tape	O
.	O
</s>
<s>
The	O
multi-user	O
versions	O
of	O
BASIC	O
(	O
EDU20	O
and	O
EDU25	O
)	O
differ	O
only	O
in	O
whether	O
or	O
not	O
they	O
support	O
block-replaceable	O
devices	O
(	O
DECtape	O
or	O
disk	B-Device
)	O
.	O
</s>
<s>
Due	O
to	O
cost	O
constraints	O
,	O
many	O
PDP-8s	B-Device
have	O
punched	O
paper	O
tape	O
readers	O
as	O
their	O
only	O
mass-storage	O
I/O	O
device	O
.	O
</s>
<s>
EDU20	O
loads	O
from	O
paper	O
tape	O
and	O
can	O
do	O
output	O
to	O
a	O
paper	O
tape	O
writer	O
if	O
the	O
machine	O
has	O
one	O
,	O
whereas	O
EDU25	O
understands	O
the	O
structure	O
of	O
a	O
filesystem	B-Application
,	O
can	O
load	O
from	O
DECtape	O
or	O
disk	B-Device
,	O
and	O
can	O
create	O
files	O
on	O
DECtape	O
or	O
disk	B-Device
.	O
</s>
<s>
Both	O
can	O
run	O
multiple	O
BASIC	O
programs	O
simultaneously	O
using	O
a	O
primitive	O
task-scheduler	O
that	O
round-robins	B-Algorithm
among	O
the	O
attached	O
terminals	O
.	O
</s>
<s>
Memory	O
is	O
always	O
tight	O
because	O
the	O
PDP-8	B-Device
uses	O
core	O
memory	O
,	O
which	O
was	O
extremely	O
expensive	O
compared	O
to	O
RAM	O
technology	O
.	O
</s>
<s>
In	O
8K	O
of	O
12-bit	B-Device
words	O
EDU20	O
can	O
support	O
up	O
to	O
4	O
terminals	O
at	O
once	O
,	O
although	O
more	O
memory	O
was	O
recommended	O
.	O
</s>
<s>
EDU25	O
requires	O
an	O
additional	O
4K	O
memory	O
bank	O
(	O
for	O
a	O
minimum	O
of	O
12K	O
)	O
because	O
the	O
code	O
contains	O
a	O
disk	B-Device
device	B-Application
driver	I-Application
and	O
a	O
filesystem	B-Application
handler	O
.	O
</s>
<s>
While	O
running	O
,	O
EDU20	O
and	O
EDU25	O
are	O
self-contained	O
programs	O
that	O
do	O
n't	O
use	O
any	O
OS/8	B-Operating_System
system	O
calls	O
.	O
</s>
<s>
Immediately	O
upon	O
being	O
invoked	O
from	O
the	O
OS/8	B-Operating_System
command	O
interpreter	O
,	O
they	O
overwrite	O
OS/8	B-Operating_System
'	O
s	O
entire	O
resident	O
portion	O
-	O
all	O
256	O
words	O
of	O
it	O
.	O
</s>
<s>
Upon	O
startup	O
,	O
EDU25	O
saves	O
the	O
contents	O
of	O
memory	O
to	O
DECtape	O
or	O
disk	B-Device
and	O
restores	O
it	O
upon	O
exit	O
.	O
</s>
<s>
In	O
addition	O
to	O
a	O
freely	O
available	O
FORTRAN	B-Application
II	O
compiler	O
,	O
there	O
is	O
also	O
a	O
rather	O
complete	O
FORTRAN	B-Application
IV	I-Application
compiler	O
available	O
.	O
</s>
<s>
This	O
compiler	O
generates	O
code	O
for	O
the	O
optional	O
FPP-8	O
floating-point	O
processor	O
,	O
which	O
is	O
essentially	O
a	O
separate	O
CPU	O
,	O
only	O
sharing	O
memory	O
with	O
the	O
PDP-8	B-Device
CPU	O
.	O
</s>
<s>
With	O
the	O
FPP-8	O
option	O
installed	O
,	O
the	O
FORTRAN	B-Application
runtime	O
code	O
detects	O
it	O
and	O
uses	O
the	O
FPP-8	O
to	O
run	O
the	O
main	O
program	O
code	O
,	O
and	O
the	O
PDP-8	B-Device
CPU	O
runs	O
as	O
an	O
I/O	O
processor	O
.	O
</s>
<s>
Lacking	O
the	O
FPP-8	O
,	O
the	O
runtime	O
code	O
instead	O
calls	O
an	O
FPP-8	O
interpreter	O
running	O
on	O
the	O
PDP-8	B-Device
CPU	O
,	O
so	O
the	O
program	O
runs	O
at	O
reduced	O
speed	O
.	O
</s>
<s>
This	O
FORTRAN	B-Application
IV	I-Application
compiler	O
in	O
version	O
1	O
has	O
the	O
interesting	O
bug	O
that	O
DO	O
loops	O
counted	O
incorrectly	O
:	O
DO	O
loops	O
would	O
count	O
1	O
,	O
2	O
,	O
3	O
,	O
5	O
,	O
6	O
,	O
7	O
,…	O
(	O
skipping	O
4	O
)	O
.	O
</s>
