<s>
KDF9	B-Device
was	O
an	O
early	O
British	O
48-bit	O
computer	O
designed	O
and	O
built	O
by	O
English	O
Electric	O
(	O
which	O
in	O
1968	O
was	O
merged	O
into	O
International	O
Computers	O
Limited	O
(	O
ICL	O
)	O
)	O
.	O
</s>
<s>
The	O
KDF9	B-Device
was	O
designed	O
for	O
,	O
and	O
used	O
almost	O
entirely	O
in	O
,	O
the	O
mathematical	O
and	O
scientific	O
processing	O
fields	O
in	O
1967	O
,	O
nine	O
were	O
in	O
use	O
in	O
UK	O
universities	O
and	O
technical	O
colleges	O
.	O
</s>
<s>
The	O
KDF8	B-Device
,	O
developed	O
in	O
parallel	O
,	O
was	O
aimed	O
at	O
commercial	O
processing	O
workloads	O
.	O
</s>
<s>
The	O
KDF9	B-Device
was	O
an	O
early	O
example	O
of	O
a	O
machine	O
that	O
directly	O
supported	O
multiprogramming	O
,	O
using	O
offsets	O
into	O
its	O
core	B-General_Concept
memory	I-General_Concept
to	O
separate	O
the	O
programs	O
into	O
distinct	O
virtual	O
address	O
spaces	O
.	O
</s>
<s>
Several	O
operating	B-General_Concept
systems	I-General_Concept
were	O
developed	O
for	O
the	O
platform	O
,	O
including	O
some	O
that	O
provided	O
fully	O
interactive	O
use	O
through	O
PDP-8	B-Device
machines	O
acting	O
as	O
smart	O
terminal	B-Device
servers	I-Device
.	O
</s>
<s>
A	O
number	O
of	O
compilers	B-Language
were	O
available	O
,	O
notably	O
both	O
checkout	O
and	O
globally	O
optimizing	O
compilers	B-Language
for	O
Algol	B-Language
60	I-Language
.	O
</s>
<s>
The	O
logic	O
circuits	O
of	O
the	O
KDF9	B-Device
were	O
entirely	O
solid-state	O
.	O
</s>
<s>
The	O
KDF9	B-Device
used	O
transformer-coupled	O
diode	B-General_Concept
–	I-General_Concept
transistor	I-General_Concept
logic	I-General_Concept
,	O
built	O
from	O
germanium	O
diodes	O
,	O
about	O
20,000	O
transistors	O
,	O
and	O
about	O
2,000	O
toroid	O
pulse	O
transformers	O
.	O
</s>
<s>
The	O
maximum	O
configuration	O
incorporated	O
32K	O
words	O
of	O
48-bit	O
core	O
storage	O
(	O
192K	O
bytes	B-Application
)	O
with	O
a	O
cycle	O
time	O
of	O
6	O
microseconds	O
.	O
</s>
<s>
Each	O
word	O
could	O
hold	O
a	O
single	O
48-bit	O
integer	O
or	O
floating-point	B-Algorithm
number	I-Algorithm
,	O
two	O
24-bit	O
integer	O
or	O
floating-point	B-Algorithm
numbers	I-Algorithm
,	O
six	O
8-bit	O
instruction	O
syllables	B-General_Concept
,	O
or	O
eight	O
6-bit	O
characters	O
.	O
</s>
<s>
There	O
was	O
also	O
provision	O
for	O
efficient	O
handling	O
of	O
double-word	O
(	O
96-bit	O
)	O
numbers	O
in	O
both	O
integer	O
and	O
floating	B-Algorithm
point	I-Algorithm
formats	I-Algorithm
.	O
</s>
<s>
However	O
,	O
there	O
was	O
no	O
facility	O
for	O
byte	B-Application
or	O
character	O
addressing	O
,	O
so	O
that	O
non-numerical	O
work	O
suffered	O
by	O
comparison	O
.	O
</s>
<s>
Its	O
standard	O
character	O
set	O
was	O
a	O
version	O
of	O
the	O
Friden	B-Application
Flexowriter	I-Application
paper	O
tape	O
code	O
that	O
was	O
oriented	O
to	O
Algol60	B-Language
,	O
and	O
included	O
unusual	O
characters	O
such	O
as	O
the	O
Algol	O
subscript	O
10	O
.	O
</s>
<s>
Three	O
additional	O
Nest	O
levels	O
and	O
one	O
additional	O
SJNS	O
level	O
were	O
reserved	O
to	O
Director	O
,	O
the	O
Operating	B-General_Concept
System	I-General_Concept
,	O
allowing	O
short-path	O
interrupts	O
to	O
be	O
handled	O
without	O
explicit	O
register	O
saving	O
and	O
restoring	O
.	O
</s>
<s>
Instructions	O
were	O
of	O
1	O
,	O
2	O
or	O
3	O
syllables	B-General_Concept
.	O
</s>
<s>
Most	O
arithmetic	O
took	O
place	O
at	O
the	O
top	O
of	O
the	O
Nest	O
and	O
used	O
zero-address	B-Application
,	O
1-syllable	O
instructions	O
,	O
although	O
address	O
arithmetic	O
and	O
index	O
updating	O
were	O
handled	O
separately	O
in	O
the	O
Qstore	O
.	O
</s>
<s>
QStore	O
handling	O
,	O
and	O
some	O
memory	O
reference	O
instructions	O
used	O
2	O
syllables	B-General_Concept
.	O
</s>
<s>
Memory	O
reference	O
instructions	O
with	O
a	O
16-bit	O
address	O
offset	O
,	O
most	O
jump	O
instructions	O
,	O
and	O
16-bit	O
literal	O
load	O
instructions	O
,	O
all	O
used	O
3	O
syllables	B-General_Concept
.	O
</s>
<s>
This	O
did	O
much	O
to	O
offset	O
the	O
relatively	O
slow	O
core	O
cycle	O
time	O
,	O
giving	O
the	O
KDF9	B-Device
about	O
a	O
third	O
of	O
the	O
speed	O
of	O
its	O
much	O
more	O
famous	O
,	O
but	O
8	O
times	O
more	O
expensive	O
and	O
much	O
less	O
commercially	O
successful	O
contemporary	O
,	O
the	O
Manchester/Ferranti	O
Atlas	O
Computer	O
.	O
</s>
<s>
The	O
KDF9	B-Device
was	O
one	O
of	O
the	O
earliest	O
fully	O
hardware-secured	O
multiprogramming	O
systems	O
.	O
</s>
<s>
Up	O
to	O
four	O
programs	O
could	O
be	O
run	O
at	O
once	O
under	O
the	O
control	O
of	O
its	O
elegantly	O
simple	O
operating	B-General_Concept
system	I-General_Concept
,	O
the	O
Timesharing	O
Director	O
,	O
each	O
being	O
confined	O
to	O
its	O
own	O
core	O
area	O
by	O
BA	O
(	O
Base	O
Address	O
)	O
and	O
NOL	O
(	O
Number	O
of	O
Locations	O
)	O
registers	O
.	O
</s>
<s>
Later	O
operating	B-General_Concept
systems	I-General_Concept
,	O
including	O
Eldon	O
2	O
at	O
the	O
University	O
of	O
Leeds	O
,	O
and	O
COTAN	O
,	O
developed	O
by	O
UKAEA	O
Culham	O
Laboratories	O
with	O
the	O
collaboration	O
of	O
Glasgow	O
University	O
,	O
were	O
fully	O
interactive	O
multi-access	O
systems	O
,	O
with	O
PDP-8	B-Device
front	O
ends	O
to	O
handle	O
the	O
terminals	O
.	O
</s>
<s>
The	O
Kidsgrove	O
and	O
Whetstone	O
Algol	B-Language
60	I-Language
compilers	B-Language
were	O
among	O
the	O
first	O
of	O
their	O
class	O
.	O
</s>
<s>
The	O
Kidsgrove	O
compiler	B-Language
stressed	O
optimization	O
;	O
the	O
Whetstone	O
compiler	B-Language
produced	O
an	O
interpretive	O
object	O
code	O
aimed	O
at	O
debugging	O
.	O
</s>
<s>
Machine	O
code	O
orders	O
were	O
written	O
in	O
a	O
form	O
of	O
octal	O
officially	O
named	O
syllabic	B-Device
octal	I-Device
(	O
also	O
known	O
as	O
'	O
slob-octal	O
'	O
or	O
'	O
slob	O
 '	O
notation	O
,	O
)	O
.	O
</s>
<s>
Although	O
the	O
word	O
'	O
byte	B-Application
 '	O
had	O
been	O
coined	O
by	O
the	O
designers	O
of	O
the	O
IBM	B-Device
7030	I-Device
Stretch	I-Device
for	O
a	O
group	O
of	O
eight	O
bits	O
,	O
it	O
was	O
not	O
yet	O
well	O
known	O
,	O
and	O
English	O
Electric	O
used	O
the	O
word	O
'	O
syllable	B-General_Concept
 '	O
for	O
what	O
is	O
now	O
called	O
a	O
byte	B-Application
.	O
</s>
<s>
Within	O
English	O
Electric	O
,	O
its	O
predecessor	O
,	O
DEUCE	B-Device
,	O
had	O
a	O
well-used	O
matrix	O
scheme	O
based	O
on	O
GIP	O
(	O
General	O
Interpretive	O
Programme	O
)	O
.	O
</s>
<s>
The	O
unreliability	O
of	O
valve	O
machines	O
led	O
to	O
the	O
inclusion	O
of	O
a	O
sum-check	B-Error_Name
mechanism	O
to	O
detect	O
errors	O
in	O
matrix	O
operations	O
.	O
</s>
<s>
The	O
scheme	O
used	O
block	O
floating-point	B-Algorithm
using	O
fixed-point	O
arithmetic	O
hardware	O
,	O
in	O
which	O
the	O
sum-checks	O
were	O
precise	O
.	O
</s>
<s>
However	O
,	O
when	O
the	O
corresponding	O
scheme	O
was	O
implemented	O
on	O
KDF9	B-Device
,	O
it	O
used	O
floating	B-Algorithm
point	I-Algorithm
,	O
a	O
new	O
concept	O
that	O
had	O
only	O
limited	O
mathematical	O
analysis	O
.	O
</s>
<s>
It	O
quickly	O
became	O
clear	O
that	O
sum	B-Error_Name
checks	I-Error_Name
were	O
no	O
longer	O
precise	O
and	O
a	O
project	O
was	O
established	O
in	O
an	O
attempt	O
to	O
provide	O
a	O
usable	O
check	O
.	O
</s>
<s>
(	O
In	O
floating	B-Algorithm
point	I-Algorithm
(	O
A	O
+	O
B	O
)	O
+	O
C	O
is	O
not	O
necessarily	O
the	O
same	O
as	O
A	O
+	O
(	O
B	O
+	O
C	O
)	O
i.e.	O
</s>
<s>
Consequently	O
,	O
the	O
idea	O
of	O
sum	B-Error_Name
checks	I-Error_Name
was	O
abandoned	O
.	O
</s>
<s>
There	O
is	O
a	O
legend	O
that	O
the	O
KDF9	B-Device
was	O
developed	O
as	O
project	O
KD9	O
(	O
Kidsgrove	O
Development	O
9	O
)	O
and	O
that	O
the	O
'	O
F	O
 '	O
in	O
its	O
designation	O
was	O
contributed	O
by	O
the	O
then	O
Chairman	O
after	O
a	O
long	O
and	O
tedious	O
discussion	O
on	O
what	O
to	O
name	O
the	O
machine	O
at	O
launch	O
—	O
"	O
I	O
do	O
n’t	O
care	O
if	O
you	O
call	O
it	O
the	O
F	O
—	O
"	O
.	O
</s>
<s>
(	O
See	O
also	O
KDF8	B-Device
for	O
the	O
parallel	O
development	O
and	O
use	O
of	O
a	O
commercially	O
oriented	O
computer	O
.	O
)	O
</s>
<s>
The	O
EGDON	O
operating	B-General_Concept
system	I-General_Concept
was	O
so	O
named	O
because	O
one	O
was	O
going	O
to	O
UKAEA	O
Winfrith	O
:	O
in	O
Thomas	O
Hardy	O
's	O
book	O
The	O
Return	O
of	O
the	O
Native	O
Winfrith	O
Heath	O
is	O
called	O
Egdon	O
Heath	O
.	O
</s>
