<s>
The	O
Burroughs	B-Language
B2500	I-Language
through	O
Burroughs	O
B4900	O
was	O
a	O
series	O
of	O
mainframe	B-Architecture
computers	I-Architecture
developed	O
and	O
manufactured	O
by	O
Burroughs	O
Corporation	O
in	O
Pasadena	O
,	O
California	O
,	O
United	O
States	O
,	O
from	O
1966	O
to	O
1991	O
.	O
</s>
<s>
They	O
were	O
aimed	O
at	O
the	O
business	O
world	O
with	O
an	O
instruction	O
set	O
optimized	O
for	O
the	O
COBOL	B-Application
programming	I-Application
language	I-Application
.	O
</s>
<s>
They	O
were	O
also	O
known	O
as	O
Burroughs	B-Language
Medium	I-Language
Systems	I-Language
,	O
by	O
contrast	O
with	O
the	O
Burroughs	B-Device
Large	I-Device
Systems	I-Device
and	O
Burroughs	B-Device
Small	I-Device
Systems	I-Device
.	O
</s>
<s>
They	O
operated	O
directly	O
on	O
COBOL-68	O
'	O
s	O
primary	O
decimal	O
data	O
types	O
:	O
strings	O
of	O
up	O
to	O
100	O
digits	O
,	O
with	O
one	O
EBCDIC	B-Language
or	O
ASCII	B-Protocol
digit	O
character	O
or	O
two	O
4-bit	O
binary-coded	O
decimal	O
BCD	O
digits	O
per	O
byte	O
.	O
</s>
<s>
Portable	O
COBOL	B-Application
programs	O
did	O
not	O
use	O
binary	O
integers	O
at	O
all	O
,	O
so	O
the	O
B2500	O
did	O
not	O
either	O
,	O
not	O
even	O
for	O
memory	O
addresses	O
.	O
</s>
<s>
Floating	B-Algorithm
point	I-Algorithm
numbers	I-Algorithm
also	O
used	O
base	O
10	O
rather	O
than	O
some	O
binary	O
base	O
,	O
and	O
had	O
up	O
to	O
100	O
mantissa	O
digits	O
.	O
</s>
<s>
A	O
typical	O
COBOL	B-Application
statement	O
'	O
ADD	O
A	O
,	O
B	O
GIVING	O
C	O
 '	O
may	O
use	O
operands	O
of	O
different	O
lengths	O
,	O
different	O
digit	O
representations	O
,	O
and	O
different	O
sign	O
representations	O
.	O
</s>
<s>
EBCDIC	B-Language
to	O
ASCII	B-Protocol
)	O
conversion	O
table	O
into	O
that	O
buffer	O
"	O
and	O
"	O
sort	O
this	O
table	O
using	O
these	O
sort	O
requirements	O
into	O
that	O
table	O
"	O
.	O
</s>
<s>
(	O
Resumption	O
is	O
a	O
prerequisite	O
for	O
doing	O
page	O
style	O
virtual	B-Architecture
memory	I-Architecture
when	O
operands	O
cross	O
page	O
boundaries	O
.	O
)	O
</s>
<s>
The	O
machine	O
matched	O
COBOL	B-Application
so	O
closely	O
that	O
the	O
COBOL	B-Application
compiler	O
was	O
simple	O
and	O
fast	O
,	O
and	O
COBOL	B-Application
programmers	O
found	O
it	O
easy	O
to	O
do	O
assembly	B-Language
programming	I-Language
as	O
well	O
.	O
</s>
<s>
Serial	O
arithmetic	O
worked	O
very	O
well	O
for	O
COBOL	B-Application
.	O
</s>
<s>
The	O
third	O
index	B-General_Concept
register	I-General_Concept
was	O
dedicated	O
to	O
pointing	O
at	O
the	O
current	O
procedure	O
's	O
stack	O
frame	O
on	O
the	O
call/return	O
stack	O
.	O
</s>
<s>
The	O
B2500	O
had	O
a	O
maximum	O
of	O
60K	O
bytes	O
of	O
core	B-General_Concept
memory	I-General_Concept
and	O
a	O
2	O
microsecond	O
cycle	O
time	O
.	O
</s>
<s>
The	O
B2500/B3500	O
machines	O
were	O
followed	O
by	O
B2700/B3700/B4700	O
in	O
1972	O
;	O
The	O
B2800/B3800/B4800	O
in	O
1976	O
,	O
The	O
B2900/B3900/B4900	O
in	O
1980	O
(	O
which	O
was	O
the	O
first	O
of	O
the	O
range	O
to	O
load	O
its	O
microcode	B-Device
from	O
floppy	B-Device
disk	I-Device
,	O
rather	O
than	O
implementing	O
it	O
as	O
hardware	O
read-only	B-Device
memory	I-Device
)	O
and	O
finally	O
the	O
Unisys	B-Language
V	I-Language
Series	I-Language
machines	O
V340-V560	O
in	O
1985-90	O
.	O
</s>
<s>
Machines	O
prior	O
to	O
the	O
B4800	O
had	O
no	O
cache	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
To	O
compensate	O
for	O
this	O
,	O
the	O
B3700/B4700	O
generation	O
used	O
semiconductor	B-Architecture
main	I-Architecture
memory	I-Architecture
that	O
was	O
faster	O
but	O
more	O
expensive	O
and	O
power	O
hungry	O
than	O
the	O
DRAM	O
used	O
in	O
competing	O
machines	O
.	O
</s>
<s>
The	O
unusual	O
use	O
of	O
decimal	O
numbers	O
as	O
memory	O
addresses	O
was	O
initially	O
no	O
problem	O
;	O
it	O
merely	O
involved	O
using	O
1-in-5	O
rather	O
than	O
1-in-8	O
decoder	O
logic	O
in	O
the	O
core	B-General_Concept
memory	I-General_Concept
's	O
row	O
selects	O
and	O
bank	O
selects	O
.	O
</s>
<s>
But	O
later	O
machines	O
used	O
standard	O
memory	B-Architecture
chips	I-Architecture
that	O
expected	O
binary	O
addresses	O
.	O
</s>
<s>
But	O
for	O
denser	O
chips	O
and	O
larger	O
total	O
memories	O
,	O
the	O
entire	O
decimal	O
address	O
had	O
to	O
be	O
crunched	O
into	O
a	O
shorter	O
quasi	O
binary	O
form	O
before	O
sending	O
the	O
address	O
to	O
the	O
chips	O
,	O
and	O
done	O
again	O
for	O
each	O
cache	B-General_Concept
or	O
memory	O
cycle	O
.	O
</s>
<s>
And	O
all	O
floating	B-Algorithm
point	I-Algorithm
operations	O
were	O
limited	O
to	O
17	O
digits	O
of	O
precision	O
.	O
</s>
<s>
Later	O
Medium	O
Systems	O
machines	O
added	O
an	O
accumulator	B-General_Concept
register	O
and	O
accumulator/memory	O
instructions	O
using	O
32-bit	O
,	O
7-digit	O
integers	O
and	O
48-bit	O
or	O
80-bit	O
floating	B-Algorithm
point	I-Algorithm
values	I-Algorithm
,	O
all	O
aligned	O
on	O
16-bit	O
word	O
boundaries	O
.	O
</s>
<s>
It	O
shared	O
many	O
architectural	O
features	O
with	O
the	O
MCP	O
of	O
Burroughs	O
 '	O
Large	O
Systems	O
stack	O
machines	O
,	O
but	O
was	O
entirely	O
different	O
internally	O
,	O
and	O
was	O
coded	O
in	O
assembly	B-Language
language	I-Language
,	O
not	O
an	O
ALGOL	B-Language
derivative	O
.	O
</s>
<s>
Programs	O
had	O
separate	O
address	O
spaces	O
dynamically	O
relocated	O
by	O
a	O
base	B-General_Concept
register	I-General_Concept
,	O
but	O
otherwise	O
there	O
was	O
no	O
virtual	B-Architecture
memory	I-Architecture
;	O
no	O
paging	B-Architecture
and	O
no	O
segmentation	B-General_Concept
.	O
</s>
<s>
Larger	O
programs	O
were	O
squeezed	O
into	O
the	O
limited	O
code	O
address	O
space	O
by	O
explicit	O
overlays	B-General_Concept
.	O
</s>
<s>
Instructions	O
 '	O
address	O
fields	O
were	O
extended	O
from	O
five	O
digits	O
to	O
six	O
digits	O
,	O
and	O
four	O
more	O
real	O
index	B-General_Concept
registers	I-General_Concept
were	O
added	O
.	O
</s>
<s>
Early	O
machines	O
used	O
Burroughs	O
's	O
head-per-track	O
disk	B-Device
systems	O
rather	O
than	O
the	O
now-standard	O
movable	O
head	O
platter	O
disks	B-Device
.	O
</s>
<s>
In	O
one	O
attempt	O
to	O
speed	O
up	O
MCP	O
,	O
its	O
overlays	B-General_Concept
were	O
carefully	O
laid	O
out	O
so	O
that	O
the	O
likely-next	O
overlays	B-General_Concept
would	O
soon	O
arrive	O
at	O
their	O
read	O
head	O
just	O
after	O
the	O
current	O
overlay	B-General_Concept
completed	O
.	O
</s>
<s>
But	O
this	O
turned	O
out	O
to	O
be	O
impractical	O
to	O
maintain	O
after	O
software	O
changes	O
,	O
and	O
better	O
results	O
were	O
consistently	O
achieved	O
with	O
a	O
totally	O
randomized	O
layout	O
of	O
all	O
MCP	O
overlays	B-General_Concept
.	O
</s>
<s>
Other	O
than	O
the	O
operating	O
system	O
itself	O
,	O
all	O
system	O
software	O
was	O
coded	O
in	O
BPL	O
(	O
Burroughs	O
Programming	O
Language	O
)	O
,	O
a	O
systems	O
programming	O
language	O
derived	O
from	O
ALGOL	B-Language
and	O
Large	O
System	O
's	O
ESPOL	B-Language
systems	O
language	O
.	O
</s>
<s>
The	O
initial	O
COBOL	B-Application
compiler	O
supported	O
the	O
ANSI	O
68	O
specification	O
and	O
supported	O
the	O
ENTER	O
SYMBOLIC	O
syntax	O
to	O
allow	O
inline	O
assembly	B-Language
language	I-Language
coding	O
,	O
but	O
lacked	O
support	O
for	O
RELATIVE	O
and	O
INDEXED	O
file	O
support	O
;	O
these	O
were	O
later	O
added	O
into	O
the	O
ANSI	O
74	O
version	O
of	O
the	O
compiler	O
,	O
which	O
was	O
released	O
in	O
1982	O
.	O
</s>
<s>
MCP	O
allowed	O
programs	O
to	O
communicate	O
with	O
each	O
other	O
via	O
core-to-core	O
transmissions	O
(	O
CRCR	O
)	O
or	O
by	O
using	O
storage	O
queues	O
(	O
STOQ	O
)	O
,	O
implemented	O
as	O
system	B-Operating_System
calls	I-Operating_System
using	O
the	O
BCT	O
instruction	O
and	O
exposed	O
to	O
the	O
languages	O
(	O
COBOL	B-Application
FILL	O
FROM/INTO	O
)	O
.	O
</s>
<s>
This	O
was	O
unheard	O
of	O
except	O
on	O
the	O
very	O
largest	O
IBM	B-Application
System/360	I-Application
systems	O
of	O
the	O
time	O
,	O
and	O
even	O
then	O
it	O
was	O
a	O
major	O
operational	O
headache	O
to	O
manage	O
the	O
interactions	O
of	O
the	O
multiple	O
program	O
streams	O
.	O
</s>
<s>
With	O
the	O
Medium	O
System	O
,	O
a	O
computer	O
could	O
be	O
simultaneously	O
running	O
a	O
batch	O
payroll	O
system	O
,	O
inputting	O
bank	O
checks	O
on	O
a	O
MICR	O
reader	O
sorter	O
,	O
compiling	O
COBOL	B-Application
applications	O
,	O
supporting	O
on-line	O
transactions	O
,	O
and	O
doing	O
test	O
runs	O
on	O
new	O
applications	O
(	O
colloquially	O
called	O
'	O
the	O
mix	O
 '	O
,	O
as	O
the	O
console	O
command	O
'	O
MX	O
 '	O
would	O
shows	O
that	O
jobs	O
were	O
executing	O
)	O
.	O
</s>
<s>
Medium	O
System	O
installations	O
often	O
had	O
tape	B-Architecture
clusters	O
(	O
four	O
drives	O
integrated	O
into	O
a	O
mid-height	O
cabinet	O
)	O
for	O
magnetic	O
tape	B-Architecture
input	O
and	O
output	O
.	O
</s>
<s>
Free-standing	O
tape	B-Architecture
drives	O
were	O
also	O
available	O
,	O
but	O
they	O
were	O
much	O
more	O
expensive	O
.	O
</s>
<s>
Tape	B-Architecture
was	O
a	O
major	O
storage	O
medium	O
on	O
these	O
computers	O
,	O
in	O
early	O
days	O
it	O
was	O
often	O
used	O
for	O
father-son	O
batch	O
updating	O
;	O
with	O
additional	O
disk	B-Device
becoming	O
cheaper	O
as	O
time	O
moved	O
on	O
it	O
became	O
relegated	O
as	O
a	O
library/backup	O
device	O
that	O
contained	O
all	O
the	O
data	O
files	O
and	O
sometimes	O
the	O
program	O
files	O
(	O
using	O
the	O
MFSOLT	O
utility	B-Application
)	O
for	O
a	O
particular	O
application	O
or	O
customer/client	O
.	O
</s>
