<s>
The	O
Compatible	B-Operating_System
Time-Sharing	I-Operating_System
System	I-Operating_System
(	O
CTSS	O
)	O
was	O
the	O
first	O
general	O
purpose	O
time-sharing	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Compatible	O
Time	B-General_Concept
Sharing	I-General_Concept
referred	O
to	O
time	B-General_Concept
sharing	I-General_Concept
which	O
was	O
compatible	O
with	O
batch	B-General_Concept
processing	I-General_Concept
;	O
it	O
could	O
offer	O
both	O
time	B-General_Concept
sharing	I-General_Concept
and	O
batch	B-General_Concept
processing	I-General_Concept
concurrently	O
.	O
</s>
<s>
CTSS	O
was	O
first	O
demonstrated	O
on	O
MIT	O
's	O
modified	O
IBM	B-Device
709	I-Device
in	O
November	O
1961	O
.	O
</s>
<s>
The	O
hardware	O
was	O
replaced	O
with	O
a	O
modified	O
IBM	B-Device
7090	I-Device
in	O
1962	O
and	O
later	O
a	O
modified	O
IBM	B-Device
7094	I-Device
called	O
the	O
"	O
blue	O
machine	O
"	O
to	O
distinguish	O
it	O
from	O
the	O
Project	O
MAC	O
CTSS	O
IBM	B-Device
7094	I-Device
.	O
</s>
<s>
A	O
second	O
deployment	O
of	O
CTSS	O
on	O
a	O
separate	O
IBM	B-Device
7094	I-Device
that	O
was	O
received	O
in	O
October	O
1963	O
(	O
the	O
"	O
red	O
machine	O
"	O
)	O
was	O
used	O
early	O
on	O
in	O
Project	O
MAC	O
until	O
1969	O
when	O
the	O
red	O
machine	O
was	O
moved	O
to	O
the	O
Information	O
Processing	O
Center	O
and	O
operated	O
until	O
July	O
20	O
,	O
1973	O
.	O
</s>
<s>
John	O
Backus	O
said	O
in	O
the	O
1954	O
summer	O
session	O
at	O
MIT	O
that	O
"	O
By	O
time	B-General_Concept
sharing	I-General_Concept
,	O
a	O
big	O
computer	O
could	O
be	O
used	O
as	O
several	O
small	O
ones	O
;	O
there	O
would	O
need	O
to	O
be	O
a	O
reading	O
station	O
for	O
each	O
user	O
"	O
.	O
</s>
<s>
Computers	O
at	O
that	O
time	O
,	O
like	O
IBM	B-Device
704	I-Device
,	O
were	O
not	O
powerful	O
enough	O
to	O
implement	O
such	O
system	O
,	O
but	O
at	O
the	O
end	O
of	O
1958	O
,	O
MIT	O
's	O
Computation	O
Center	O
nevertheless	O
added	O
a	O
typewriter	O
input	O
to	O
its	O
704	O
with	O
the	O
intent	O
that	O
a	O
programmer	O
or	O
operator	O
could	O
"	O
obtain	O
additional	O
answers	O
from	O
the	O
machine	O
on	O
a	O
time-sharing	B-General_Concept
basis	O
with	O
other	O
programs	O
using	O
the	O
machine	O
simultaneously	O
"	O
.	O
</s>
<s>
In	O
June	O
1959	O
,	O
Christopher	O
Strachey	O
published	O
a	O
paper	O
"	O
Time	B-General_Concept
Sharing	I-General_Concept
in	O
Large	O
Fast	O
Computers	O
"	O
at	O
the	O
UNESCO	O
Information	O
Processing	O
Conference	O
in	O
Paris	O
,	O
where	O
he	O
envisaged	O
a	O
programmer	O
debugging	O
a	O
program	O
at	O
a	O
console	O
(	O
like	O
a	O
teletype	O
)	O
connected	O
to	O
the	O
computer	O
,	O
while	O
another	O
program	O
was	O
running	O
in	O
the	O
computer	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
Debugging	O
programs	O
was	O
an	O
important	O
problem	O
at	O
that	O
time	O
,	O
because	O
with	O
batch	B-General_Concept
processing	I-General_Concept
,	O
it	O
then	O
often	O
took	O
a	O
day	O
from	O
submitting	O
a	O
changed	O
code	O
,	O
to	O
getting	O
the	O
results	O
.	O
</s>
<s>
John	O
McCarthy	O
wrote	O
a	O
memo	O
about	O
that	O
at	O
MIT	O
,	O
after	O
which	O
a	O
preliminary	O
study	O
committee	O
and	O
a	O
working	O
committee	O
were	O
established	O
at	O
MIT	O
,	O
to	O
develop	O
time	B-General_Concept
sharing	I-General_Concept
.	O
</s>
<s>
By	O
July	O
,	O
1961	O
a	O
few	O
time	B-General_Concept
sharing	I-General_Concept
commands	O
had	O
become	O
operational	O
on	O
the	O
Computation	O
Center	O
's	O
IBM	B-Device
709	I-Device
,	O
and	O
in	O
November	O
1961	O
,	O
Fernando	O
J	O
.	O
Corbató	O
demonstrated	O
at	O
MIT	O
what	O
was	O
called	O
the	O
Experimental	O
Time-Sharing	B-General_Concept
System	I-General_Concept
.	O
</s>
<s>
Robert	O
C	O
.	O
Daley	O
,	O
Peter	O
R	O
.	O
Bos	O
and	O
at	O
least	O
6	O
other	O
programmers	O
implemented	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
partly	O
based	O
on	O
the	O
Fortran	B-Application
Monitor	I-Application
System	I-Application
.	O
</s>
<s>
The	O
system	O
used	O
an	O
IBM	B-Device
7090	I-Device
,	O
modified	O
by	O
Herbert	O
M	O
.	O
Teager	O
,	O
with	O
added	O
3	O
Flexowriters	B-Application
for	O
user	O
consoles	O
,	O
and	O
maybe	O
a	O
timer	B-Device
.	O
</s>
<s>
Each	O
of	O
the	O
3	O
users	O
had	O
two	O
tape	B-Device
units	I-Device
,	O
one	O
for	O
the	O
user	O
's	O
file	B-Application
directory	I-Application
,	O
and	O
one	O
for	O
dumping	O
the	O
core	O
(	O
program	O
in	O
memory	O
)	O
.	O
</s>
<s>
The	O
memory	O
was	O
27	O
k	O
words	O
(	O
36-bit	O
words	O
)	O
for	O
users	O
,	O
and	O
5	O
k	O
words	O
for	O
the	O
supervisor	O
(	O
operating	B-General_Concept
system	I-General_Concept
)	O
.	O
</s>
<s>
The	O
input	O
from	O
the	O
consoles	O
was	O
written	O
to	O
the	O
buffers	O
in	O
the	O
supervisor	O
,	O
by	O
interrupts	B-Application
,	O
and	O
when	O
a	O
return	O
character	O
was	O
received	O
,	O
the	O
control	O
was	O
given	O
to	O
the	O
supervisor	O
,	O
which	O
dumped	O
the	O
running	O
code	O
to	O
the	O
tape	O
and	O
decided	O
what	O
to	O
run	O
next	O
.	O
</s>
<s>
The	O
console	O
commands	O
implemented	O
at	O
the	O
time	O
were	O
login	O
,	O
logout	O
,	O
input	O
,	O
edit	O
,	O
fap	O
,	O
mad	B-Language
,	O
madtrn	O
,	O
load	O
,	O
use	O
,	O
start	O
,	O
skippm	O
,	O
listf	O
,	O
printf	O
,	O
xdump	O
and	O
xundump	O
.	O
</s>
<s>
This	O
became	O
the	O
initial	O
version	O
of	O
the	O
Compatible	B-Operating_System
Time-Sharing	I-Operating_System
System	I-Operating_System
.	O
</s>
<s>
This	O
was	O
apparently	O
the	O
first	O
ever	O
public	O
demonstration	O
of	O
time-sharing	B-General_Concept
;	O
there	O
are	O
other	O
claims	O
,	O
but	O
they	O
refer	O
to	O
special-purpose	O
systems	O
,	O
or	O
with	O
no	O
known	O
papers	O
published	O
.	O
</s>
<s>
The	O
"	O
compatibility	O
"	O
of	O
CTSS	O
was	O
with	O
background	O
jobs	O
run	O
on	O
the	O
same	O
computer	O
,	O
which	O
generally	O
used	O
more	O
of	O
the	O
compute	O
resources	O
than	O
the	O
time-sharing	B-General_Concept
functions	O
.	O
</s>
<s>
As	O
MIT	O
CTSS	O
was	O
an	O
academic	O
system	O
,	O
a	O
research	O
vehicle	O
and	O
not	O
a	O
system	O
for	O
commercial	O
computing	O
,	O
two	O
years	O
later	O
a	O
version	O
of	O
DOTSYS	O
stripped	O
of	O
CTSS	O
dependencies	O
for	O
software	O
portability	O
was	O
used	O
on	O
an	O
IBM	B-Device
709	I-Device
at	O
the	O
American	O
Printing	O
House	O
for	O
the	O
Blind	O
to	O
print	O
the	O
first	O
braille	O
edition	O
of	O
a	O
book	O
produced	O
from	O
teletypesetter	O
input	O
,	O
only	O
a	O
few	O
weeks	O
after	O
the	O
ink-print	O
version	O
.	O
</s>
<s>
A	O
short	O
FORTRAN	B-Application
II	O
program	O
was	O
written	O
to	O
produce	O
a	O
conversion	O
table	O
from	O
inches	O
to	O
millimeters	O
in	O
braille	O
via	O
the	O
BRAILLEMBOSS	O
braille	O
page	O
printer	O
.	O
</s>
<s>
A	O
deployment	O
of	O
three	O
BRISC	O
CRT	B-Device
consoles	O
for	O
testing	O
at	O
the	O
MIT	O
Engineering	O
Library	O
showed	O
that	O
it	O
was	O
preferred	O
over	O
two	O
other	O
systems	O
,	O
ARDS	O
and	O
DATEL	O
.	O
</s>
<s>
The	O
original	O
ELIZA	B-Application
ran	O
on	O
CTSS	O
.	O
</s>
<s>
CTSS	O
had	O
one	O
of	O
the	O
first	O
computerized	O
text	O
editing	O
and	O
formatting	O
utilities	O
,	O
called	O
TYPSET	B-Protocol
and	I-Protocol
RUNOFF	I-Protocol
(	O
the	O
successors	O
of	O
MEMO	O
,	O
MODIFY	O
and	O
DITTO	O
)	O
.	O
</s>
<s>
CTSS	O
had	O
one	O
of	O
the	O
first	O
instant	B-Application
messaging	I-Application
systems	O
similar	O
to	O
write	B-Device
.	O
</s>
<s>
MIT	O
Computation	O
Center	O
staff	O
member	O
Louis	O
Pouzin	O
created	O
for	O
CTSS	O
a	O
command	O
called	O
RUNCOM	B-Device
,	O
which	O
executed	O
a	O
list	O
of	O
commands	O
contained	O
in	O
a	O
file	B-Operating_System
.	O
</s>
<s>
RUNCOM	B-Device
also	O
provided	O
for	O
parameter	O
substitution	O
.	O
</s>
<s>
He	O
later	O
created	O
a	O
design	O
for	O
the	O
Multics	B-Application
shell	B-Operating_System
that	O
was	O
implemented	O
by	O
Glenda	O
Schroeder	O
which	O
in	O
turn	O
inspired	O
Unix	B-Language
shell	I-Language
scripts	I-Language
.	O
</s>
<s>
CTSS	O
had	O
an	O
implementation	O
of	O
the	O
text	O
editor	O
QED	B-Application
,	O
the	O
predecessor	O
of	O
ed	O
,	O
vi	B-Application
,	O
and	O
vim	O
,	O
with	O
regular	O
expressions	O
added	O
by	O
Ken	O
Thompson	O
.	O
</s>
<s>
CTSS	O
used	O
a	O
modified	O
IBM	B-Device
7090	I-Device
mainframe	O
computer	O
that	O
had	O
two	O
32,768	O
(	O
32K	O
)	O
36-bit-word	O
banks	O
of	O
core	B-General_Concept
memory	I-General_Concept
instead	O
of	O
the	O
default	O
configuration	O
which	O
provides	O
only	O
one	O
.	O
</s>
<s>
One	O
bank	O
was	O
reserved	O
for	O
the	O
time-sharing	B-General_Concept
supervisory	O
program	O
,	O
the	O
other	O
for	O
user	O
programs	O
.	O
</s>
<s>
CTSS	O
had	O
a	O
protected-mode	O
kernel	O
,	O
the	O
supervisor	O
's	O
functions	O
in	O
the	O
A-core	O
(	O
memory	O
bank	O
A	O
)	O
could	O
be	O
called	O
only	O
by	O
software	O
interrupts	B-Application
,	O
like	O
in	O
the	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Causing	O
memory-protection	O
interrupts	B-Application
were	O
used	O
for	O
software	O
interrupts	B-Application
.	O
</s>
<s>
Processor	B-General_Concept
allocation	O
scheduling	O
with	O
a	O
quantum	O
time	O
unit	O
200	O
ms	O
,	O
was	O
controlled	O
by	O
a	O
multilevel	B-Operating_System
feedback	I-Operating_System
queue	I-Operating_System
.	O
</s>
<s>
It	O
also	O
had	O
some	O
special	O
memory-management	O
hardware	O
,	O
a	O
clock	O
interrupt	B-Application
and	O
the	O
ability	O
to	O
trap	B-Application
certain	O
instructions	O
.	O
</s>
<s>
CTSS	O
at	O
first	O
had	O
only	O
an	O
assembler	O
,	O
FAP	O
,	O
and	O
a	O
compiler	O
,	O
MAD	B-Language
.	O
</s>
<s>
Also	O
,	O
Fortran	B-Application
II	O
code	O
could	O
be	O
translated	O
into	O
MAD	B-Language
code	O
by	O
using	O
MADTRN	O
.	O
</s>
<s>
Later	O
half	O
of	O
the	O
system	O
was	O
written	O
in	O
MAD	B-Language
.	O
</s>
<s>
Later	O
there	O
were	O
other	O
programming	O
languages	O
including	O
COMIT	B-Language
II	I-Language
,	O
LISP	B-Language
1.5	I-Language
and	O
a	O
version	O
of	O
ALGOL	B-Language
.	O
</s>
<s>
Each	O
user	O
had	O
their	O
own	O
directory	B-Application
,	O
and	O
there	O
were	O
also	O
shared	O
directories	B-Application
for	O
groups	O
of	O
people	O
with	O
the	O
same	O
"	O
problem	O
number	O
"	O
.	O
</s>
<s>
Each	O
file	B-Operating_System
had	O
two	O
names	O
,	O
the	O
second	O
indicating	O
its	O
type	O
as	O
did	O
the	O
extension	O
in	O
later	O
system	O
.	O
</s>
<s>
At	O
first	O
,	O
each	O
file	B-Operating_System
could	O
have	O
one	O
of	O
four	O
modes	O
:	O
temporary	O
,	O
permanent	O
,	O
read-only	O
class	O
1	O
,	O
and	O
read-only	O
class	O
2	O
.	O
</s>
<s>
Read-only	O
class	O
1	O
allowed	O
the	O
user	O
to	O
change	O
the	O
mode	O
of	O
the	O
file	B-Operating_System
.	O
</s>
<s>
Files	O
could	O
also	O
be	O
symbolically	O
linked	O
between	O
directories	B-Application
.	O
</s>
<s>
A	O
directory	B-Application
listing	O
by	O
listf	O
:	O
</s>
<s>
An	O
IBM	O
7750	O
transmission	O
control	O
unit	O
capable	O
of	O
supporting	O
up	O
to	O
112	O
teleprinter	O
terminals	O
,	O
including	O
IBM	B-Device
1050	I-Device
Selectrics	O
and	O
Model	O
35s	O
.	O
</s>
<s>
Some	O
of	O
the	O
terminals	O
were	O
located	O
remotely	O
,	O
and	O
the	O
system	O
could	O
be	O
accessed	O
using	O
the	O
public	O
Telex	B-Application
and	I-Application
TWX	I-Application
networks	O
.	O
</s>
<s>
CTSS	O
was	O
described	O
in	O
a	O
paper	O
presented	O
at	O
the	O
1962	O
Spring	O
Joint	O
Computer	O
Conference	O
,	O
and	O
greatly	O
influenced	O
the	O
design	O
of	O
other	O
early	O
time-sharing	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Maurice	O
Wilkes	O
witnessed	O
CTSS	O
and	O
the	O
design	O
of	O
the	O
Titan	B-Device
Supervisor	I-Device
was	O
inspired	O
by	O
that	O
.	O
</s>
<s>
Multics	B-Application
,	O
which	O
was	O
also	O
developed	O
by	O
Project	O
MAC	O
,	O
was	O
started	O
in	O
the	O
1960s	O
as	O
a	O
successor	O
to	O
CTSS	O
–	O
and	O
in	O
turn	O
inspired	O
the	O
development	O
of	O
Unix	O
in	O
1969	O
.	O
</s>
<s>
One	O
of	O
the	O
technical	O
terms	O
inherited	O
by	O
these	O
systems	O
from	O
CTSS	O
is	O
daemon	B-Operating_System
.	O
</s>
<s>
Incompatible	B-Application
Timesharing	I-Application
System	I-Application
(	O
ITS	O
)	O
,	O
another	O
early	O
,	O
revolutionary	O
,	O
and	O
influential	O
MIT	O
time-sharing	B-General_Concept
system	I-General_Concept
,	O
was	O
produced	O
by	O
people	O
who	O
disagreed	O
with	O
the	O
direction	O
taken	O
by	O
CTSS	O
,	O
and	O
later	O
,	O
Multics	B-Application
;	O
the	O
name	O
was	O
a	O
parody	O
of	O
"	O
CTSS	O
"	O
,	O
as	O
later	O
the	O
name	O
"	O
Unix	O
"	O
was	O
a	O
parody	O
of	O
"	O
Multics	B-Application
"	O
.	O
</s>
<s>
CTSS	O
and	O
ITS	O
file	B-Operating_System
systems	O
have	O
a	O
number	O
of	O
design	O
elements	O
in	O
common	O
.	O
</s>
<s>
(	O
master	O
file	B-Application
directory	I-Application
)	O
and	O
one	O
or	O
more	O
U.F.D.	O
</s>
<s>
(	O
user	O
file	B-Application
directories	I-Application
)	O
.	O
</s>
<s>
Neither	O
of	O
them	O
have	O
nested	O
directories	B-Application
(	O
sub-directories	O
)	O
.	O
</s>
<s>
Both	O
have	O
file	B-Operating_System
names	O
consisting	O
of	O
two	O
names	O
which	O
are	O
a	O
maximum	O
of	O
six-characters	O
long	O
.	O
</s>
