<s>
ICT	O
1900	O
was	O
a	O
family	O
of	O
mainframe	B-Architecture
computers	I-Architecture
released	O
by	O
International	O
Computers	O
and	O
Tabulators	O
(	O
ICT	O
)	O
and	O
later	O
International	O
Computers	O
Limited	O
(	O
ICL	O
)	O
during	O
the	O
1960s	O
and	O
1970s	O
.	O
</s>
<s>
The	O
1900	O
series	O
was	O
notable	O
for	O
being	O
one	O
of	O
the	O
few	O
non-American	O
competitors	O
to	O
the	O
IBM	B-Application
System/360	I-Application
,	O
enjoying	O
significant	O
success	O
in	O
the	O
European	O
and	O
British	O
Commonwealth	O
markets	O
.	O
</s>
<s>
In	O
order	O
to	O
sweeten	O
the	O
deal	O
,	O
Ferranti	O
demonstrated	O
to	O
ICT	O
the	O
Ferranti-Packard	B-Device
6000	I-Device
(	O
FP6000	O
)	O
machine	O
,	O
which	O
had	O
been	O
developed	O
by	O
its	O
Canadian	O
subsidiary	O
Ferranti-Packard	O
,	O
to	O
a	O
design	O
known	O
as	O
Harriac	O
that	O
had	O
been	O
initiated	O
in	O
Ferranti	O
by	O
Harry	O
Johnson	O
and	O
fleshed	O
out	O
by	O
Stanley	O
Gill	O
and	O
John	O
Iliffe	O
.	O
</s>
<s>
ICT	O
considered	O
using	O
the	O
FP6000	O
as	O
their	O
medium-sized	O
processor	O
in	O
the	O
1965	O
–	O
1968	O
timeframe	O
,	O
replacing	O
the	O
ICT	B-Device
1302	I-Device
.	O
</s>
<s>
Another	O
plan	O
being	O
considered	O
was	O
to	O
license	O
a	O
new	B-Device
range	I-Device
of	O
machines	O
being	O
developed	O
by	O
RCA	O
,	O
probably	O
compatible	O
with	O
the	O
expected	O
IBM	B-Device
8000	I-Device
.	O
</s>
<s>
On	O
7	O
April	O
1964	O
IBM	O
announced	O
the	O
System/360	B-Application
series	O
,	O
a	O
family	O
of	O
compatible	O
machines	O
spanning	O
nearly	O
the	O
complete	O
range	O
of	O
customer	O
needs	O
.	O
</s>
<s>
Two	O
paths	O
were	O
available	O
:	O
develop	O
a	O
range	O
of	O
machines	O
based	O
on	O
the	O
FP6000	O
,	O
using	O
the	O
flexibility	O
of	O
its	O
design	O
to	O
produce	O
smaller	O
or	O
larger	O
machines	O
,	O
or	O
cooperate	O
with	O
RCA	O
who	O
were	O
re-targeting	O
their	O
development	O
to	O
a	O
System/360	B-Application
compatible	O
range	O
to	O
be	O
known	O
as	O
the	O
RCA	B-Device
Spectra	I-Device
70	I-Device
.	O
</s>
<s>
The	O
centrepiece	O
of	O
the	O
new	B-Device
range	I-Device
was	O
the	O
ICT	O
1904	O
,	O
a	O
version	O
of	O
the	O
FP6000	O
with	O
the	O
ICT	O
standard	O
peripheral	O
interface	O
.	O
</s>
<s>
The	O
first	O
commercial	O
sale	O
was	O
made	O
in	O
1964	O
to	O
the	O
Morgan	O
Crucible	O
Company	O
,	O
comprising	O
a	O
16K	O
word	O
1902	O
with	O
an	O
80-column	O
980-card/minute	O
reader	O
,	O
a	O
card	B-Architecture
punch	O
,	O
a	O
600	O
line/min	O
printer	O
and	O
4	O
x	O
20kchar/s	O
tape	O
drives	O
.	O
</s>
<s>
It	O
was	O
soon	O
upgraded	O
to	O
a	O
32K	O
word	O
memory	O
and	O
a	O
floating	B-Algorithm
point	I-Algorithm
unit	O
to	O
allow	O
for	O
some	O
scientific	O
work	O
.	O
</s>
<s>
The	O
ICT	O
1900	O
was	O
a	O
word-addressing	B-General_Concept
machine	O
using	O
a	O
register-to-memory	O
architecture	O
with	O
eight	O
accumulator	O
registers	O
.	O
</s>
<s>
Three	O
of	O
the	O
accumulators	O
could	O
be	O
used	O
as	O
modifier	O
(	O
index	B-General_Concept
)	O
registers	O
.	O
</s>
<s>
The	O
accumulators	O
were	O
addressable	O
as	O
if	O
they	O
were	O
the	O
first	O
eight	O
words	O
of	O
memory	O
,	O
giving	O
the	O
effect	O
of	O
register-to-register	O
instructions	O
with	O
no	O
extra	O
operation	O
codes	O
being	O
needed	O
.	O
</s>
<s>
Later	O
models	O
added	O
paging	B-Architecture
hardware	O
,	O
allowing	O
true	O
virtual	B-Architecture
memory	I-Architecture
with	O
the	O
GEORGE	B-General_Concept
4	I-General_Concept
operating	O
system	O
.	O
</s>
<s>
Instructions	O
contained	O
a	O
12-bit	O
operand	O
,	O
either	O
fixed	O
or	O
offset	O
from	O
an	O
index	B-General_Concept
register	I-General_Concept
.	O
</s>
<s>
When	O
the	O
address	O
size	O
was	O
increased	O
to	O
22	O
bits	O
,	O
replaced	O
(	O
indirect	B-Language
)	O
and	O
relative	O
branches	O
were	O
added	O
to	O
the	O
instruction	O
set	O
to	O
allow	O
access	O
to	O
the	O
larger	O
address	O
space	O
.	O
</s>
<s>
User	O
processes	O
communicated	O
with	O
the	O
executive	O
using	O
extracodes	B-Device
,	O
instructions	O
that	O
caused	O
a	O
trap	B-Application
into	O
the	O
executive	O
.	O
</s>
<s>
On	O
smaller	O
members	O
of	O
the	O
series	O
,	O
some	O
expensive	O
instructions	O
(	O
floating	B-Algorithm
point	I-Algorithm
for	O
example	O
)	O
were	O
also	O
implemented	O
as	O
extracodes	B-Device
.	O
</s>
<s>
The	O
hardware	O
floating-point	B-Algorithm
unit	O
,	O
if	O
fitted	O
,	O
ran	O
autonomously	O
.	O
</s>
<s>
After	O
a	O
floating-point	B-Algorithm
operation	O
was	O
started	O
,	O
integer	O
instructions	O
could	O
be	O
run	O
in	O
parallel	O
until	O
the	O
result	O
of	O
the	O
floating-point	B-Algorithm
operation	O
was	O
needed	O
.	O
</s>
<s>
Two-bit	O
character	O
offset	O
,	O
seven-bit	O
counter	O
and	O
15-bit	O
modifier	O
(	O
word	B-General_Concept
address	I-General_Concept
)	O
.	O
</s>
<s>
The	O
BCHX	O
(	O
branch	O
on	O
character	O
indexing	O
)	O
instruction	O
decremented	O
the	O
counter	O
and	O
incremented	O
the	O
character	O
offset	O
,	O
incrementing	O
the	O
word	B-General_Concept
address	I-General_Concept
if	O
the	O
character	O
offset	O
overflowed	O
,	O
branching	O
if	O
the	O
count	O
had	O
not	O
reached	O
zero	O
.	O
</s>
<s>
In	O
22-bit	O
addressing	O
mode	O
the	O
counter	O
was	O
unavailable	O
,	O
and	O
the	O
format	O
was	O
a	O
two-bit	O
character	O
offset	O
and	O
a	O
22-bit	O
word	B-General_Concept
address	I-General_Concept
.	O
</s>
<s>
The	O
BCHX	O
instruction	O
incremented	O
the	O
character	O
offset	O
,	O
incremented	O
the	O
word	B-General_Concept
address	I-General_Concept
if	O
the	O
character	O
offset	O
overflowed	O
,	O
and	O
branched	O
unconditionally	O
.	O
</s>
<s>
A	O
24-bit	O
two	B-General_Concept
's	I-General_Concept
complement	I-General_Concept
signed	O
number	O
.	O
</s>
<s>
The	O
first	O
word	O
held	O
a	O
24-bit	O
two	B-General_Concept
's	I-General_Concept
complement	I-General_Concept
signed	O
number	O
,	O
subsequent	O
words	O
held	O
23-bit	O
extensions	O
with	O
the	O
high	O
bit	O
used	O
for	O
internal	O
carry	B-Algorithm
.	O
</s>
<s>
Two	O
words	O
holding	O
a	O
24-bit	O
signed	O
argument	O
(	O
mantissa	B-Algorithm
)	O
and	O
a	O
nine-bit	O
exponent	O
.	O
</s>
<s>
Handled	O
in	O
software	O
on	O
all	O
but	O
1906/7	O
processors	O
with	O
the	O
extended	O
floating-point	B-Algorithm
feature	O
.	O
</s>
<s>
In	O
order	O
to	O
deal	O
with	O
data	O
on	O
paper	O
tape	O
or	O
from	O
communications	O
equipment	O
,	O
a	O
system	O
of	O
shifts	O
could	O
be	O
used	O
to	O
represent	O
the	O
full	O
128	O
characters	O
of	O
ASCII	B-Protocol
.	O
</s>
<s>
Thus	O
the	O
ASCII	B-Protocol
string	O
"	O
Hello	O
World	O
"	O
would	O
be	O
encoded	O
as	O
"	O
αHβELLO	O
αWβORLD	O
"	O
.	O
</s>
<s>
The	O
1900	O
used	O
a	O
variant	O
of	O
ASCII-63	O
,	O
known	O
by	O
ICT	O
as	O
the	O
ECMA	O
character	O
set	O
,	O
with	O
differences	O
in	O
five	O
character	O
codes	O
:	O
</s>
<s>
Both	O
the	O
1900	O
series	O
and	O
IBM	B-Application
System/360	I-Application
provided	O
hardware	O
support	O
for	O
multi-programming	B-Operating_System
.	O
</s>
<s>
On	O
the	O
1900	O
,	O
all	O
user	O
memory	O
addresses	O
were	O
modified	O
by	O
a	O
datum	O
(	O
base	O
address	O
)	O
register	B-General_Concept
and	O
checked	O
against	O
a	O
limit	O
register	B-General_Concept
,	O
preventing	O
one	O
program	O
interfering	O
with	O
another	O
.	O
</s>
<s>
The	O
System/360	B-Application
gave	O
each	O
process	O
and	O
every	O
2048-byte	O
block	O
of	O
memory	O
a	O
four-bit	O
key	O
,	O
and	O
if	O
a	O
process	O
key	O
did	O
not	O
match	O
the	O
memory	O
block	O
key	O
an	O
exception	O
would	O
result	O
.	O
</s>
<s>
The	O
System/360	B-Application
had	O
the	O
advantage	O
of	O
a	O
larger	O
word	O
and	O
character	O
size	O
;	O
its	O
32-bit	O
words	O
were	O
large	O
enough	O
for	O
(	O
low	O
accuracy	O
)	O
floating	B-Algorithm
point	I-Algorithm
numbers	I-Algorithm
whereas	O
the	O
1900	O
needed	O
at	O
least	O
two	O
words	O
.	O
</s>
<s>
The	O
eight-bit	O
byte	O
of	O
the	O
System/360	B-Application
allowed	O
manipulation	O
of	O
lowercase	O
characters	O
without	O
the	O
complex	O
shift	O
sequences	O
of	O
the	O
1900	O
.	O
</s>
<s>
A	O
very	O
small	O
machine	O
with	O
a	O
6-bit	O
wide	O
mill	O
(	O
arithmetic	B-General_Concept
unit	I-General_Concept
)	O
.	O
</s>
<s>
The	O
1901	O
was	O
announced	O
and	O
released	O
after	O
the	O
other	O
members	O
of	O
the	O
initial	O
range	O
,	O
in	O
response	O
to	O
the	O
IBM	B-Device
System/360	I-Device
Model	I-Device
20	I-Device
,	O
and	O
was	O
a	O
great	O
success	O
.	O
</s>
<s>
Like	O
the	O
1901	O
the	O
1902	O
performed	O
multiply	O
and	O
divide	O
operations	O
as	O
extracodes	B-Device
.	O
</s>
<s>
An	O
optional	O
floating	B-Algorithm
point	I-Algorithm
unit	O
,	O
the	O
scientific	O
computing	O
facility	O
,	O
SCF	O
was	O
also	O
available	O
as	O
a	O
super-set	O
of	O
the	O
CCF	O
.	O
</s>
<s>
A	O
1904	O
with	O
an	O
autonomous	O
hardware	O
floating	B-Algorithm
point	I-Algorithm
unit	O
.	O
</s>
<s>
A	O
1906	O
with	O
a	O
floating	B-Algorithm
point	I-Algorithm
unit	O
.	O
</s>
<s>
Designed	O
for	O
Universities	O
who	O
needed	O
floating	B-Algorithm
point	I-Algorithm
but	O
found	O
the	O
1905	O
too	O
expensive	O
.	O
</s>
<s>
The	O
execution	O
time	O
for	O
an	O
addition	O
instruction	O
(	O
"	O
add	O
the	O
contents	O
of	O
store	O
location	O
x	O
to	O
register	B-General_Concept
y	O
"	O
)	O
ranged	O
from	O
2.5	O
μs	O
for	O
a	O
1906	O
or	O
1907	O
with	O
1.1	O
μs	O
core	O
store	O
,	O
to	O
34	O
μs	O
for	O
a	O
1901	O
with	O
6	O
μs	O
core	O
store	O
.	O
</s>
<s>
All	O
machines	O
except	O
the	O
1901	O
were	O
operated	O
from	O
a	O
modified	O
Teletype	B-Application
Model	I-Application
33	I-Application
ASR	O
used	O
to	O
give	O
commands	O
to	O
the	O
executive	O
.	O
</s>
<s>
A	O
range	O
of	O
peripherals	O
was	O
available	O
,	O
including	O
80-column	B-Architecture
card	I-Architecture
punches	O
and	O
readers	O
,	O
8	O
track	O
paper	O
tape	O
punches	O
and	O
readers	O
and	O
solid	O
barrel	O
line	O
printers	O
.	O
</s>
<s>
Magnetic	B-Architecture
disk	I-Architecture
storage	O
became	O
available	O
in	O
1966	O
.	O
</s>
<s>
The	O
1904E	O
with	O
a	O
floating	B-Algorithm
point	I-Algorithm
unit	O
.	O
</s>
<s>
A	O
1906E	O
with	O
a	O
special	O
higher	O
performance	O
floating	B-Algorithm
point	I-Algorithm
unit	O
.	O
</s>
<s>
(	O
ICT	O
merged	O
with	O
English	B-Device
Electric	I-Device
Computers	I-Device
to	O
form	O
ICL	O
on	O
9	O
July	O
1968	O
.	O
</s>
<s>
The	O
original	O
discrete	O
germanium	O
semiconductor	O
implementations	O
were	O
replaced	O
by	O
Texas	O
Instruments	O
7400	O
series	O
TTL	B-General_Concept
integrated	O
circuits	O
in	O
most	O
of	O
the	O
range	O
and	O
Motorola	O
MECL	O
10K	O
ECL	B-General_Concept
integrated	O
circuits	O
in	O
the	O
new	O
1906A	O
(	O
which	O
was	O
based	O
on	O
the	O
original	O
1906	O
rather	O
than	O
the	O
dual	O
processor	O
1904	O
of	O
the	O
1906E/F	O
)	O
.	O
</s>
<s>
There	O
was	O
a	O
proposal	O
to	O
build	O
a	O
multiprocessor	O
version	O
of	O
the	O
1906A	O
,	O
the	O
1908A	O
(	O
known	O
internally	O
as	O
Project	O
51	O
)	O
,	O
which	O
would	O
allow	O
ICL	O
to	O
compete	O
with	O
the	O
large	O
CDC	O
and	O
IBM	O
machines	O
in	O
Universities	O
and	O
research	O
centers	O
but	O
it	O
was	O
eventually	O
abandoned	O
in	O
favor	O
of	O
accelerating	O
work	O
on	O
the	O
New	B-Device
Range	I-Device
which	O
was	O
being	O
designed	O
to	O
replace	O
both	O
the	O
1900	O
series	O
and	O
the	O
ICL	B-Device
System	I-Device
4	I-Device
.	O
</s>
<s>
With	O
the	O
A	O
series	O
a	O
hardware	O
floating	B-Algorithm
point	I-Algorithm
unit	O
was	O
made	O
an	O
optional	O
feature	O
of	O
all	O
machines	O
,	O
instead	O
of	O
having	O
a	O
different	O
model	O
number	O
for	O
floating	B-Algorithm
point	I-Algorithm
equipped	O
machines	O
.	O
</s>
<s>
ICL	O
introduced	O
a	O
paging	B-Architecture
unit	O
to	O
the	O
higher	O
end	O
machines	O
(	O
1904A	O
,	O
1906A	O
)	O
and	O
a	O
new	O
version	O
of	O
the	O
GEORGE	B-General_Concept
operating	O
system	O
,	O
GEORGE	B-General_Concept
4	I-General_Concept
which	O
was	O
compatible	O
with	O
GEORGE	B-General_Concept
3	I-General_Concept
but	O
used	O
paged	O
virtual	B-Architecture
memory	I-Architecture
in	O
place	O
of	O
the	O
simple	O
base/limit	O
system	O
of	O
the	O
earlier	O
machines	O
.	O
</s>
<s>
The	O
1904A	O
had	O
an	O
optional	O
paging	B-Architecture
unit	O
and	O
so	O
could	O
run	O
GEORGE	B-General_Concept
4	I-General_Concept
.	O
</s>
<s>
The	O
1906A	O
had	O
a	O
paging	B-Architecture
unit	O
and	O
so	O
could	O
run	O
GEORGE	B-General_Concept
4	I-General_Concept
.	O
</s>
<s>
In	O
April	O
1971	O
ICL	O
announced	O
the	O
S	O
series	O
of	O
machines	O
,	O
replacing	O
the	O
core	O
store	O
of	O
the	O
earlier	O
machines	O
with	O
semiconductor	O
memory	O
in	O
most	O
of	O
the	O
range	O
and	O
very	O
fast	O
Plessey	O
nickel	O
plated	B-General_Concept
wire	I-General_Concept
memory	I-General_Concept
for	O
the	O
top	O
of	O
the	O
range	O
1906S	O
.	O
</s>
<s>
Nickel	O
plated	B-General_Concept
wire	I-General_Concept
memory	I-General_Concept
with	O
a	O
250ns	O
cycle	O
speed	O
.	O
</s>
<s>
As	O
the	O
larger	O
models	O
of	O
the	O
new	B-Device
range	I-Device
were	O
being	O
introduced	O
it	O
was	O
decided	O
that	O
the	O
lower	O
models	O
of	O
the	O
1900	O
range	O
were	O
becoming	O
uncompetitive	O
.	O
</s>
<s>
As	O
the	O
1903T	O
was	O
based	O
on	O
the	O
1904S	O
it	O
was	O
available	O
with	O
a	O
paging	B-Architecture
unit	O
and	O
could	O
run	O
George	B-General_Concept
4	I-General_Concept
.	O
</s>
<s>
During	O
and	O
after	O
the	O
production	O
of	O
the	O
1900	O
series	O
a	O
number	O
of	O
compatible	O
(	O
or	O
clone	B-General_Concept
)	O
machines	O
were	O
produced	O
by	O
ICL	O
licensees	O
,	O
as	O
well	O
as	O
competitors	O
.	O
</s>
<s>
In	O
1969	O
IBM	O
had	O
introduced	O
the	O
System/3	B-Device
entry-level	O
machine	O
,	O
which	O
began	O
to	O
cut	O
into	O
sales	O
of	O
the	O
ICL	O
1901	O
and	O
1902	O
models	O
.	O
</s>
<s>
Despite	O
their	O
New	B-Device
Range	I-Device
numbering	O
,	O
these	O
machines	O
used	O
the	O
ICL	O
1900	O
instruction	O
set	O
and	O
ran	O
1900	O
software	O
,	O
although	O
a	O
microprogram	B-Device
was	O
available	O
that	O
provided	O
an	O
IBM-360	O
instruction	O
set	O
to	O
allow	O
them	O
to	O
run	O
IBM	O
software	O
.	O
</s>
<s>
The	O
2903/2904	O
were	O
released	O
with	O
an	O
RPG	B-Language
compiler	O
to	O
better	O
compete	O
with	O
System/3	B-Device
.	O
</s>
<s>
An	O
EMMY	O
processor	O
emulating	B-Application
the	O
IBM	B-Application
360	I-Application
order	O
code	O
was	O
estimated	O
to	O
be	O
around	O
the	O
speed	O
of	O
an	O
IBM	B-Device
System/360	I-Device
Model	I-Device
50	I-Device
,	O
implying	O
that	O
the	O
ME29	O
was	O
faster	O
than	O
the	O
original	O
ICT	O
1904	O
,	O
approaching	O
the	O
speed	O
of	O
the	O
ICT	O
1906	O
.	O
</s>
<s>
In	O
an	O
effort	O
to	O
increase	O
sales	O
to	O
ICL	O
customers	O
,	O
and	O
to	O
profit	O
from	O
the	O
difficulties	O
ICL	O
were	O
having	O
moving	O
customers	O
from	O
the	O
1900	O
to	O
the	O
New	B-Device
Range	I-Device
,	O
IBM	O
introduced	O
a	O
microcode	B-Device
package	O
for	O
the	O
370/145	B-Device
allowing	O
execution	O
of	O
1900	O
series	O
programs	O
.	O
</s>
<s>
The	O
Odra	B-Device
1300	O
series	O
(	O
Odra	B-Device
1304	O
,	O
Odra	B-Device
1305	O
and	O
Odra	B-Device
1325	O
)	O
were	O
a	O
range	O
of	O
1900	O
compatible	O
machines	O
built	O
by	O
Elwro	O
in	O
Wrocław	O
,	O
Poland	O
between	O
1971	O
and	O
1978	O
.	O
</s>
<s>
By	O
agreement	O
with	O
ICL	O
the	O
Odra	B-Device
machines	O
ran	O
standard	O
ICL	O
software	O
(	O
executive	O
E6RM	O
,	O
George	B-General_Concept
3	I-General_Concept
)	O
.	O
</s>
<s>
Second	O
generation	O
"	O
S3E	O
"	O
(	O
microcoded	B-Device
)	O
versions	O
of	O
the	O
larger	O
New	B-Device
Range	I-Device
systems	O
(	O
such	O
as	O
the	O
2960/2966	O
from	O
West	O
Gorton	O
,	O
and	O
the	O
later	O
2940/50	O
from	O
Stevenage	O
)	O
,	O
could	O
run	O
1900	O
series	O
code	O
under	O
DME	O
(	O
Direct	B-Operating_System
Machine	I-Operating_System
Environment	I-Operating_System
)	O
as	O
an	O
emulation	B-Application
as	O
well	O
as	O
the	O
New	B-Device
Range	I-Device
instruction	O
set	O
under	O
the	O
newer	O
VME	B-General_Concept
(	O
Virtual	O
Machine	O
Environment	O
)	O
.	O
</s>
<s>
Later	O
CME	O
(	O
Concurrent	O
Machine	O
Environment	O
)	O
microcode	B-Device
was	O
developed	O
,	O
which	O
allowed	O
DME	O
and	O
VME	B-General_Concept
to	O
co-exist	O
(	O
and	O
run	O
)	O
concurrently	O
on	O
the	O
same	O
platform	O
,	O
similar	O
to	O
the	O
functionality	O
offered	O
by	O
virtualisation	B-General_Concept
software	O
such	O
as	O
VMware	O
today	O
.	O
</s>
<s>
The	O
FP6000	O
ran	O
under	O
the	O
control	O
of	O
operators	O
executive	O
,	O
a	O
simple	O
operating	O
system	O
that	O
allowed	O
the	O
operator	O
using	O
the	O
system	O
console	O
to	O
load	O
programs	O
from	O
magnetic	O
tape	O
,	O
cards	B-Architecture
or	O
paper	O
tape	O
,	O
allocate	O
peripherals	O
to	O
programs	O
and	O
attribute	O
priorities	O
to	O
running	O
programs	O
.	O
</s>
<s>
Despite	O
its	O
simplicity	O
executive	O
was	O
,	O
for	O
the	O
time	O
,	O
quite	O
powerful	O
,	O
allocating	O
memory	O
to	O
programs	O
as	O
needed	O
(	O
rather	O
than	O
the	O
fixed	O
partitions	O
provided	O
by	O
OS/360	B-Application
)	O
.	O
</s>
<s>
This	O
was	O
possible	O
because	O
the	O
FP6000	O
design	O
contained	O
hardware	O
to	O
aid	O
multi-programming	B-Operating_System
,	O
datum	O
and	O
limit	O
registers	O
which	O
made	O
programs	O
address	O
independent	O
and	O
avoided	O
one	O
program	O
accessing	O
the	O
memory	O
allocated	O
to	O
another	O
.	O
</s>
<s>
To	O
allow	O
more	O
efficient	O
use	O
of	O
peripherals	O
,	O
as	O
well	O
running	O
multiple	O
programs	O
simultaneously	O
,	O
executive	O
allowed	O
a	O
limited	O
multi-threading	B-General_Concept
within	O
programs	O
(	O
each	O
program	O
could	O
be	O
split	O
into	O
up	O
to	O
four	O
sub-programs	O
,	O
sharing	O
the	O
same	O
address	O
space	O
,	O
which	O
were	O
also	O
time	O
shared	O
.	O
</s>
<s>
An	O
important	O
task	O
of	O
these	O
different	O
versions	O
was	O
to	O
hide	O
the	O
hardware	O
differences	O
between	O
the	O
different	O
machines	O
,	O
providing	O
emulation	B-Application
of	O
missing	O
instructions	O
as	O
extracodes	B-Device
.	O
</s>
<s>
With	O
the	O
introduction	O
of	O
magnetic	B-Architecture
disk	I-Architecture
systems	O
executive	O
became	O
more	O
complex	O
,	O
using	O
overlaying	B-General_Concept
to	O
reduce	O
its	O
memory	O
footprint	O
.	O
</s>
<s>
The	O
branch	O
was	O
initially	O
staffed	O
with	O
people	O
being	O
released	O
by	O
the	O
end	O
of	O
work	O
on	O
the	O
OMP	O
operating	O
system	O
for	O
the	O
Ferranti	B-Device
Orion	I-Device
.	O
</s>
<s>
The	O
initial	O
design	O
of	O
the	O
new	O
system	O
,	O
named	O
George	B-General_Concept
in	O
part	O
after	O
George	B-General_Concept
E	O
.	O
Felton	O
,	O
head	O
of	O
the	O
Basic	O
Programming	O
Division	O
,	O
was	O
based	O
on	O
ideas	O
from	O
the	O
Orion	O
and	O
the	O
spooling	B-Device
system	O
of	O
the	O
Atlas	B-Device
computer	I-Device
.	O
</s>
<s>
The	O
initial	O
versions	O
,	O
George	B-General_Concept
1	I-General_Concept
(	O
for	O
the	O
ICT	O
1901	O
,	O
1902	O
and	O
1903	O
machines	O
)	O
was	O
a	O
simple	O
batch	B-General_Concept
processing	I-General_Concept
system	O
.	O
</s>
<s>
Job	O
descriptions	O
were	O
read	O
in	O
from	O
cards	B-Architecture
or	O
paper	O
tape	O
,	O
peripherals	O
and	O
magnetic	O
tape	O
files	O
were	O
dynamically	O
allocated	O
to	O
the	O
job	O
which	O
was	O
then	O
run	O
,	O
producing	O
output	O
on	O
the	O
line	O
printer	O
.	O
</s>
<s>
George	B-General_Concept
2	I-General_Concept
added	O
the	O
concept	O
of	O
spooling	B-Device
.	O
</s>
<s>
Jobs	O
and	O
input	O
data	O
were	O
read	O
in	O
from	O
cards	B-Architecture
or	O
paper	O
tape	O
to	O
an	O
input	O
well	O
on	O
disk	O
or	O
tape	O
.	O
</s>
<s>
The	O
jobs	O
were	O
then	O
run	O
,	O
writing	O
output	O
to	O
disk	O
or	O
tape	O
spool	B-Device
files	O
,	O
which	O
were	O
then	O
written	O
to	O
the	O
output	O
peripherals	O
.	O
</s>
<s>
George	B-General_Concept
1	I-General_Concept
and	O
2	O
ran	O
as	O
simple	O
programs	O
under	O
executive	O
(	O
with	O
trusted	O
status	O
that	O
allowed	O
them	O
to	O
control	O
user	O
programs	O
)	O
.	O
</s>
<s>
George	B-General_Concept
3	I-General_Concept
was	O
a	O
complete	O
operating	O
system	O
in	O
itself	O
,	O
it	O
used	O
a	O
much	O
reduced	O
executive	O
responsible	O
only	O
for	O
handling	O
low	O
level	O
hardware	O
access	O
.	O
</s>
<s>
George	B-General_Concept
3	I-General_Concept
implemented	O
both	O
batch	B-General_Concept
processing	I-General_Concept
and	O
Multiple	O
online	O
programming	O
(	O
MOP	O
)	O
–	O
interactive	O
use	O
from	O
terminals	O
.	O
</s>
<s>
George	B-General_Concept
4	I-General_Concept
was	O
introduced	O
with	O
the	O
availability	O
of	O
paging	B-Architecture
hardware	O
on	O
the	O
later	O
machines	O
and	O
implemented	O
paged	O
virtual	B-Architecture
memory	I-Architecture
instead	O
of	O
the	O
simple	O
swapping	O
used	O
by	O
George	B-General_Concept
3	I-General_Concept
.	O
</s>
<s>
ICT	O
initially	O
provided	O
the	O
PLAN	O
assembly	B-Language
language	I-Language
and	O
later	O
the	O
"	O
big	O
three	O
"	O
high-level	O
languages	O
:	O
ALGOL	B-Language
60	I-Language
,	O
COBOL	B-Application
and	O
FORTRAN	O
66	O
.	O
</s>
<s>
Initially	O
paper	O
tape	O
and	O
cards	B-Architecture
were	O
used	O
for	O
input	O
and	O
output	O
;	O
later	O
magnetic	O
tape	O
and	O
finally	O
disk	O
files	O
.	O
</s>
<s>
Later	O
versions	O
for	O
the	O
George	B-General_Concept
3	I-General_Concept
and	O
4	O
operating	O
systems	O
expanded	O
to	O
sizes	O
as	O
large	O
as	O
48K	O
words	O
.	O
</s>
<s>
PLASYD	O
–	O
an	O
alternative	O
assembly	B-Language
language	I-Language
modeled	O
on	O
PL/360	B-Language
,	O
much	O
used	O
by	O
the	O
Atlas	B-Device
Computer	I-Device
Laboratory	O
.	O
</s>
<s>
A	O
simple	O
report	O
generation	O
language	O
in	O
the	O
RPG	B-Language
vein	O
,	O
much	O
used	O
on	O
the	O
small	O
1901	O
replacing	O
card	B-Architecture
tabulator	O
systems	O
.	O
</s>
<s>
JEAN	B-Language
–	O
a	O
dialect	O
of	O
JOSS	B-Language
,	O
a	O
conversational	O
language	O
similar	O
in	O
capabilities	O
to	O
BASIC	O
.	O
</s>
<s>
SOBS	B-Language
–	O
the	O
Southampton	B-Language
BASIC	I-Language
System	I-Language
.	O
</s>
<s>
POP-2	B-Language
–	O
from	O
the	O
University	O
of	O
Edinburgh	O
,	O
a	O
stack-based	O
list-processing	O
language	O
.	O
</s>
<s>
ALGOL	B-General_Concept
68R	I-General_Concept
–	O
the	O
Royal	O
Radar	O
Establishment	O
wrote	O
one	O
of	O
the	O
first	O
Algol	B-Language
68	I-Language
compilers	O
for	O
the	O
1900	O
.	O
</s>
<s>
Pascal	B-Application
–	O
Queen	O
's	O
University	O
Belfast	O
initially	O
ported	O
the	O
CDC	O
Pascal	B-Application
compiler	O
to	O
the	O
1900	O
,	O
then	O
wrote	O
a	O
completely	O
new	O
and	O
well-engineered	O
replacement	O
.	O
</s>
<s>
FORTRAN	O
77	O
–	O
the	O
University	O
of	O
Salford	O
produced	O
a	O
FORTRAN	O
77	O
compiler	O
for	O
George	B-General_Concept
3	I-General_Concept
.	O
</s>
<s>
It	O
was	O
unusual	O
in	O
that	O
it	O
used	O
8-bit	O
characters	O
and	O
the	O
ASCII	B-Protocol
character	I-Protocol
set	I-Protocol
internally	O
.	O
</s>
<s>
Silverfrost	B-Application
FTN95	I-Application
,	O
a	O
Fortran	O
95	O
compiler	O
for	O
Windows	O
is	O
a	O
distant	O
descendant	O
.	O
</s>
<s>
BCPL	B-Language
–	O
Bernard	B-Application
Sufrin	I-Application
ported	O
Martin	O
Richards	O
's	O
IBM	B-Application
360	I-Application
compiler	O
to	O
the	O
1900	O
architecture	O
in	O
mid-1969	O
at	O
Essex	O
University	O
.	O
</s>
<s>
BCPL	B-Language
is	O
antecedent	O
of	O
C	B-Language
.	O
</s>
<s>
Filetab	B-Language
–	O
A	O
tool	O
for	O
generating	O
reports	O
based	O
on	O
decision	O
tables	O
.	O
</s>
<s>
Filetab	B-Language
was	O
marketed	O
by	O
the	O
National	O
Computing	O
Centre	O
(	O
NCC	O
)	O
,	O
set	O
up	O
by	O
the	O
British	O
Government	O
in	O
Manchester	O
.	O
</s>
<s>
The	O
product	O
was	O
first	O
known	O
as	O
NITA	O
(	O
Nineteen	O
Hundred	O
Tabulator	O
)	O
and	O
later	O
became	O
known	O
as	O
TABN	B-Language
(	O
Tabulator	O
Nineteen	O
Hundred	O
)	O
.	O
</s>
<s>
TABN	B-Language
statements	O
were	O
either	O
interpreted	O
from	O
punched	B-Architecture
cards	I-Architecture
at	O
run-time	O
,	O
or	O
they	O
could	O
be	O
compiled	O
to	O
produce	O
a	O
program	O
that	O
could	O
simply	O
be	O
executed	O
.	O
</s>
<s>
One	O
of	O
the	O
attractions	O
of	O
writing	O
programs	O
in	O
Filetab	B-Language
was	O
its	O
short	O
development	O
time	O
.	O
</s>
