<s>
The	O
GEC	B-Device
2050	I-Device
was	O
an	O
8-bit	O
minicomputer	B-Architecture
produced	O
during	O
the	O
1970s	O
,	O
initially	O
by	O
Marconi	O
Elliott	O
Computer	O
Systems	O
of	O
the	O
UK	O
,	O
before	O
the	O
company	O
renamed	O
itself	O
GEC	B-Device
Computers	I-Device
Limited	I-Device
.	O
</s>
<s>
The	O
first	O
models	O
were	O
labeled	O
MECS	O
2050	O
,	O
before	O
being	O
renamed	O
GEC	B-Device
2050	I-Device
.	O
</s>
<s>
The	O
GEC	B-Device
2050	I-Device
was	O
commonly	O
used	O
as	O
a	O
Remote	B-Protocol
Job	I-Protocol
Entry	I-Protocol
station	O
,	O
supporting	O
a	O
punched	B-Architecture
card	I-Architecture
reader	O
,	O
line	O
printer	O
,	O
system	B-Device
console	I-Device
,	O
and	O
a	O
data	O
link	O
to	O
a	O
remote	O
mainframe	B-Architecture
computer	I-Architecture
system	O
,	O
and	O
GEC	B-Device
Computers	I-Device
sold	O
a	O
complete	O
RJE	B-Protocol
package	O
including	O
the	O
system	O
,	O
peripherals	O
,	O
and	O
RJE	B-Protocol
software	O
.	O
</s>
<s>
The	O
GEC	B-Device
2050	I-Device
supported	O
up	O
to	O
64KiB	O
of	O
magnetic-core	O
memory	O
(	O
minimum	O
4KiB	O
,	O
expandable	O
by	O
8KiB	O
and	O
16KiB	O
modules	O
)	O
.	O
</s>
<s>
The	O
system	O
had	O
a	O
single	O
Channel	B-Device
Controller	I-Device
for	O
performing	O
autonomous	O
I/O	B-General_Concept
,	O
and	O
used	O
the	O
same	O
peripheral	O
I/O	B-General_Concept
controllers	O
as	O
the	O
GEC	B-Device
4000	I-Device
series	I-Device
minicomputer	B-Architecture
.	O
</s>
<s>
Although	O
CISC	B-Architecture
,	O
the	O
instruction	B-General_Concept
set	I-General_Concept
is	O
sufficiently	O
simple	O
to	O
be	O
tabulated	O
in	O
its	O
entirety	O
:	O
</s>
<s>
Thus	O
,	O
register	O
X1	O
is	O
being	O
used	O
as	O
the	O
index	O
register	O
,	O
and	O
the	O
offset	O
,	O
v	O
,	O
is	O
specified	O
in	O
the	O
second	O
byte	B-Application
of	O
the	O
instruction	O
.	O
</s>
<s>
Again	O
,	O
the	O
offset	O
of	O
the	O
jump	O
is	O
obtained	O
from	O
the	O
second	O
byte	B-Application
of	O
the	O
instruction	O
.	O
</s>
<s>
Thus	O
,	O
all	O
instructions	O
in	O
rows	O
0	O
to	O
7	O
and	O
row	O
9	O
consist	O
of	O
two	O
bytes	B-Application
(	O
the	O
opcode	O
and	O
a	O
data	O
byte	B-Application
)	O
while	O
all	O
the	O
other	O
instructions	O
consist	O
of	O
just	O
a	O
single	O
opcode	O
byte	B-Application
.	O
</s>
<s>
The	O
main	O
accumulator	B-General_Concept
register	O
,	O
A	O
,	O
can	O
be	O
set	O
to	O
be	O
1	O
,	O
2	O
,	O
3	O
or	O
4	O
bytes	B-Application
in	O
length	O
,	O
using	O
the	O
SETL	O
instructions	O
.	O
</s>
<s>
This	O
controls	O
how	O
many	O
bytes	B-Application
are	O
loaded	O
(	O
or	O
stored	O
)	O
in	O
a	O
memory-access	O
instruction	O
.	O
</s>
<s>
The	O
JIL	O
instruction	O
performs	O
a	O
Jump	O
Indirect	O
,	O
like	O
the	O
JI	O
instruction	O
,	O
but	O
saves	O
the	O
value	O
of	O
the	O
program	B-General_Concept
counter	I-General_Concept
,	O
S	O
,	O
into	O
index	O
register	O
X2	O
.	O
</s>
<s>
More	O
complex	O
subroutine	O
calls	O
involve	O
the	O
use	O
of	O
the	O
PREP	O
instruction	O
,	O
which	O
saves	O
the	O
return	O
information	O
in	O
the	O
first	O
bytes	B-Application
of	O
the	O
current	O
memory	O
segment	O
.	O
</s>
<s>
The	O
programmer	B-Application
might	O
arrive	O
,	O
to	O
work	O
on	O
a	O
Fortran-II	O
program	O
that	O
he	O
had	O
already	O
started	O
writing	O
in	O
the	O
previous	O
session	O
,	O
carrying	O
a	O
teleprinter	O
paper	O
listing	O
of	O
that	O
program	O
that	O
has	O
been	O
annotated	O
with	O
the	O
new	O
changes	O
that	O
are	O
to	O
be	O
made	O
,	O
and	O
the	O
punch	O
tape	O
that	O
contains	O
the	O
machine-readable	O
source	O
code	O
of	O
the	O
program	O
.	O
</s>
<s>
Since	O
the	O
magnetic	O
core	O
memory	O
,	O
which	O
is	O
non-volatile	B-General_Concept
memory	I-General_Concept
,	O
would	O
generally	O
still	O
contain	O
the	O
previous	O
user	O
's	O
program	O
,	O
the	O
programmer	B-Application
might	O
need	O
to	O
load	O
the	O
punched	O
tape	O
called	O
Minisystem	O
(	O
containing	O
the	O
object	B-Language
code	I-Language
of	O
a	O
small	O
,	O
memory	O
monitor	B-General_Concept
program	I-General_Concept
)	O
.	O
</s>
<s>
The	O
text	B-Application
editor	I-Application
program	O
,	O
EDIT	O
,	O
could	O
then	O
be	O
called	O
from	O
the	O
teleprinter	O
keyboard	O
,	O
at	O
the	O
Minisystem	O
's	O
'	O
>	O
'	O
prompt	O
.	O
</s>
<s>
The	O
programmer	B-Application
would	O
then	O
load	O
the	O
source	O
tape	O
into	O
the	O
reader	O
,	O
and	O
while	O
this	O
,	O
too	O
,	O
was	O
being	O
read	O
in	O
,	O
and	O
spilled	O
out	O
all	O
over	O
the	O
floor	O
,	O
the	O
programmer	B-Application
could	O
be	O
busy	O
winding	O
up	O
the	O
Minisystem	O
tape	O
,	O
into	O
a	O
tidy	O
reel	O
again	O
,	O
using	O
a	O
hand-turned	O
winch	O
.	O
</s>
<s>
Eventually	O
,	O
once	O
the	O
source	O
tape	O
had	O
finished	O
being	O
read	O
,	O
the	O
text	B-Application
editor	I-Application
program	O
would	O
prompt	O
for	O
a	O
new	O
command	O
,	O
which	O
was	O
the	O
invitation	O
to	O
edit	O
the	O
program	O
.	O
</s>
<s>
Whilst	O
the	O
paper-tape	O
punch	O
was	O
doing	O
this	O
,	O
again	O
spilling	O
out	O
its	O
product	O
(	O
albeit	O
not	O
so	O
fast	O
as	O
the	O
reader	O
,	O
and	O
off	O
to	O
the	O
left	O
of	O
the	O
machine	O
)	O
from	O
its	O
front	O
panel	O
mounting	O
,	O
the	O
programmer	B-Application
could	O
be	O
winding	O
up	O
the	O
old	O
version	O
of	O
the	O
source	O
tape	O
,	O
for	O
it	O
to	O
be	O
kept	O
as	O
a	O
backup	O
version	O
.	O
</s>
<s>
Unfortunately	O
,	O
with	O
only	O
16	O
KiBytes	O
of	O
core	O
store	O
,	O
the	O
Minisystem	O
and	O
Fortran	B-Application
compiler	B-Language
would	O
not	O
both	O
fit	O
in	O
memory	O
together	O
,	O
so	O
the	O
next	O
stage	O
would	O
be	O
to	O
load	O
the	O
Fortran	B-Application
compiler	B-Language
tape	O
(	O
which	O
was	O
stored	O
in	O
another	O
cardboard	O
box	O
on	O
the	O
shelf	O
in	O
the	O
computer	O
room	O
)	O
.	O
</s>
<s>
It	O
would	O
be	O
loaded	O
into	O
the	O
tape	O
reader	O
once	O
the	O
compiler	B-Language
had	O
finished	O
being	O
read	O
in	O
,	O
and	O
the	O
compiler	B-Language
tape	O
would	O
be	O
wound	O
back	O
into	O
a	O
tidy	O
reel	O
.	O
</s>
<s>
The	O
first	O
pass	O
of	O
the	O
source	O
tape	O
through	O
the	O
tape	O
reader	O
was	O
generally	O
used	O
just	O
for	O
checking	O
for	O
syntax	B-Application
errors	I-Application
in	O
the	O
program	O
,	O
so	O
the	O
generation	O
of	O
the	O
object	B-Language
tape	I-Language
from	O
the	O
tape	O
punch	O
would	O
be	O
suppressed	O
.	O
</s>
<s>
This	O
time	O
,	O
it	O
would	O
be	O
read	O
in	O
,	O
haltingly	O
,	O
whilst	O
the	O
paper	O
tape	O
punch	O
worked	O
flat-out	O
to	O
produce	O
the	O
corresponding	O
object	B-Language
tape	I-Language
(	O
usually	O
two	O
or	O
three	O
times	O
longer	O
in	O
length	O
than	O
the	O
Fortran	B-Application
source	O
tape	O
)	O
.	O
</s>
<s>
The	O
linking-loader	O
program	O
,	O
LINK	O
,	O
could	O
then	O
be	O
called	O
from	O
the	O
keyboard	O
,	O
at	O
the	O
Minisystem	O
's	O
prompt	O
,	O
and	O
the	O
object	B-Language
tape	I-Language
fed	O
through	O
the	O
reader	O
.	O
</s>
<s>
The	O
linking-loader	O
also	O
required	O
the	O
library	O
tape	O
,	O
containing	O
the	O
Fortran	B-Application
library	O
functions	O
,	O
to	O
be	O
loaded	O
into	O
the	O
reader	O
.	O
</s>
<s>
Both	O
tapes	O
would	O
eventually	O
need	O
to	O
be	O
wound	O
up	O
,	O
but	O
this	O
tended	O
not	O
to	O
be	O
done	O
immediately	O
,	O
because	O
of	O
the	O
programmer	B-Application
's	O
eagerness	O
at	O
finally	O
being	O
in	O
a	O
position	O
to	O
run	O
the	O
program	O
.	O
</s>
<s>
Depending	O
on	O
what	O
happened	O
during	O
the	O
program	O
execution	O
,	O
the	O
programmer	B-Application
might	O
need	O
to	O
read	O
the	O
newest	O
source	O
tape	O
back	O
in	O
to	O
the	O
editor	O
program	O
,	O
yet	O
again	O
,	O
ready	O
to	O
go	O
round	O
the	O
software	O
development	O
cycle	O
once	O
more	O
.	O
</s>
