<s>
The	O
IBM	B-Device
305	I-Device
RAMAC	I-Device
was	O
the	O
first	O
commercial	O
computer	O
that	O
used	O
a	O
moving-head	O
hard	B-Device
disk	I-Device
drive	I-Device
(	O
magnetic	O
disk	B-Device
storage	I-Device
)	O
for	O
secondary	O
storage	O
.	O
</s>
<s>
It	O
replaced	O
a	O
huge	O
tub	B-Device
file	I-Device
which	O
was	O
part	O
of	O
MOPAR	O
's	O
parts	O
inventory	O
control	O
and	O
order	O
processing	O
system	O
.	O
</s>
<s>
The	O
system	O
featured	O
an	O
IBM	B-Device
RAMAC	I-Device
305	I-Device
computer	O
,	O
punched	B-Architecture
card	I-Architecture
data	O
collection	O
,	O
and	O
a	O
central	O
printing	O
facility	O
.	O
</s>
<s>
Production	O
ended	O
in	O
1961	O
;	O
the	O
RAMAC	O
computer	O
became	O
obsolete	O
in	O
1962	O
when	O
the	O
IBM	B-Device
1405	I-Device
Disk	B-Device
Storage	I-Device
Unit	O
for	O
the	O
IBM	B-Device
1401	I-Device
was	O
introduced	O
,	O
and	O
the	O
305	O
was	O
withdrawn	O
in	O
1969	O
.	O
</s>
<s>
The	O
first	O
hard	B-Device
disk	I-Device
unit	O
was	O
shipped	O
September	O
13	O
,	O
1956	O
.	O
</s>
<s>
IBM	O
touted	O
the	O
system	O
as	O
being	O
able	O
to	O
store	O
the	O
equivalent	O
of	O
64,000	O
punched	B-Architecture
cards	I-Architecture
.	O
</s>
<s>
The	O
305	O
was	O
one	O
of	O
the	O
last	O
vacuum	B-Architecture
tube	I-Architecture
computers	I-Architecture
that	O
IBM	O
built	O
.	O
</s>
<s>
The	O
IBM	B-Device
350	I-Device
disk	B-Device
system	O
stored	O
5	O
million	O
alphanumeric	O
characters	O
recorded	O
as	O
six	O
data	O
bits	O
,	O
one	O
parity	B-Error_Name
bit	I-Error_Name
and	O
one	O
space	O
bit	O
for	O
eight	O
bits	O
recorded	O
per	O
character	O
.	O
</s>
<s>
It	O
had	O
fifty	O
disks	B-Device
.	O
</s>
<s>
Two	O
independent	O
access	B-Device
arms	I-Device
moved	O
up	O
and	O
down	O
to	O
select	O
a	O
disk	B-Device
,	O
and	O
in	O
and	O
out	O
to	O
select	O
a	O
recording	O
track	O
,	O
all	O
under	O
servo	O
control	O
.	O
</s>
<s>
The	O
IBM	B-Device
RAMAC	I-Device
305	I-Device
system	O
with	O
350	O
disk	B-Device
storage	I-Device
leased	O
for	O
US$	O
3,200	O
(	O
)	O
per	O
month	O
.	O
</s>
<s>
The	O
original	O
305	B-Device
RAMAC	I-Device
computer	O
system	O
could	O
be	O
housed	O
in	O
a	O
room	O
of	O
about	O
9m	O
(	O
30ft	O
)	O
by	O
15m	O
(	O
50ft	O
)	O
;	O
the	O
350	O
disk	B-Device
storage	I-Device
unit	O
measured	O
around	O
.	O
</s>
<s>
Currie	O
Munce	O
,	O
research	O
vice	O
president	O
for	O
Hitachi	O
Global	O
Storage	O
Technologies	O
(	O
which	O
has	O
acquired	O
IBM	O
's	O
hard	B-Device
disk	I-Device
drive	I-Device
business	O
)	O
,	O
stated	O
in	O
a	O
Wall	O
Street	O
Journal	O
interview	O
that	O
the	O
RAMAC	O
unit	O
weighed	O
over	O
a	O
ton	O
,	O
had	O
to	O
be	O
moved	O
around	O
with	O
forklifts	O
,	O
and	O
was	O
delivered	O
via	O
large	O
cargo	O
airplanes	O
.	O
</s>
<s>
Programming	O
the	O
305	O
involved	O
not	O
only	O
writing	O
machine	B-Language
language	I-Language
instructions	B-General_Concept
to	O
be	O
stored	O
on	O
the	O
drum	B-General_Concept
memory	I-General_Concept
,	O
but	O
also	O
almost	O
every	O
unit	O
in	O
the	O
system	O
(	O
including	O
the	O
computer	O
itself	O
)	O
could	O
be	O
programmed	O
by	O
inserting	O
wire	O
jumpers	O
into	O
a	O
plugboard	O
control	O
panel	O
.	O
</s>
<s>
System	O
architecture	O
was	O
documented	O
in	O
the	O
305	B-Device
RAMAC	I-Device
Manual	O
of	O
Operation	O
.	O
</s>
<s>
The	O
305	O
was	O
a	O
character-oriented	O
variable	O
"	O
word	O
"	O
length	O
decimal	O
(	O
BCD	O
)	O
computer	O
with	O
a	O
drum	B-General_Concept
memory	I-General_Concept
rotating	O
at	O
6000RPM	O
that	O
held	O
3200	O
alphanumeric	O
characters	O
.	O
</s>
<s>
A	O
core	B-General_Concept
memory	I-General_Concept
buffer	O
of	O
100	O
characters	O
was	O
used	O
for	O
temporary	O
storage	O
during	O
data	O
transfers	O
.	O
</s>
<s>
Each	O
character	O
was	O
six	O
bits	O
plus	O
one	O
odd	B-Error_Name
parity	I-Error_Name
bit	O
(	O
"	O
R	O
"	O
)	O
composed	O
of	O
two	O
zone	O
bits	O
(	O
"	O
X	O
"	O
and	O
"	O
O	O
"	O
)	O
and	O
remaining	O
four	O
binary	O
bits	O
for	O
the	O
value	O
of	O
the	O
digit	O
in	O
the	O
following	O
format	O
:	O
</s>
<s>
Instructions	B-General_Concept
could	O
only	O
be	O
stored	O
on	O
20	O
tracks	O
of	O
the	O
drum	B-General_Concept
memory	I-General_Concept
and	O
were	O
fixed	O
length	O
(	O
10	O
characters	O
)	O
,	O
in	O
the	O
following	O
format	O
:	O
</s>
<s>
The	O
305	O
's	O
control	O
panel	O
programming	O
determines	O
the	O
action(s )	O
performed.QControl	O
code	O
;	O
modifies	O
the	O
operation	O
(	O
similar	O
to	O
an	O
op	B-Language
code	I-Language
)	O
,	O
the	O
default	O
operation	O
being	O
a	O
copy	O
from	O
source	O
to	O
destination	O
.	O
</s>
<s>
Fixed-point	O
data	O
"	O
words	O
"	O
could	O
be	O
any	O
size	O
from	O
one	O
decimal	O
digit	O
up	O
to	O
100	O
decimal	O
digits	O
,	O
with	O
the	O
X	O
bit	O
of	O
the	O
least	O
significant	O
digit	O
storing	O
the	O
sign	O
(	O
signed	B-Algorithm
magnitude	I-Algorithm
)	O
.	O
</s>
<s>
The	O
drum	B-General_Concept
memory	I-General_Concept
was	O
organized	O
into	O
32	O
tracks	O
of	O
100	O
characters	O
each	O
.	O
</s>
<s>
L	O
and	O
M	O
select	O
the	O
same	O
track	O
,	O
containing	O
ten	O
10-character	O
"	O
Accumulators	B-General_Concept
"	O
.	O
</s>
<s>
(	O
Numbers	O
in	O
these	O
accumulators	B-General_Concept
were	O
stored	O
in	O
ten	B-Algorithm
's	I-Algorithm
complement	I-Algorithm
form	O
,	O
with	O
the	O
X	O
bit	O
of	O
the	O
most	O
significant	O
digit	O
storing	O
the	O
sign	O
.	O
</s>
<s>
The	O
sign	O
of	O
each	O
accumulator	B-General_Concept
was	O
also	O
held	O
in	O
a	O
relay	O
.	O
</s>
<s>
However	O
the	O
305	O
automatically	O
converted	O
between	O
its	O
standard	O
signed	B-Algorithm
magnitude	I-Algorithm
format	O
and	O
this	O
format	O
without	O
the	O
need	O
for	O
special	O
programming	O
.	O
)	O
</s>
<s>
The	O
305	O
's	O
instruction	B-General_Concept
set	I-General_Concept
does	O
not	O
include	O
any	O
jumps	O
,	O
instead	O
these	O
are	O
programmed	O
on	O
the	O
control	O
panel	O
:	O
</s>
<s>
Conditional	O
jump	O
the	O
program	O
exit	O
code	O
(	O
P	O
field	O
)	O
specifies	O
a	O
Program	O
exit	O
hub	O
on	O
the	O
control	O
panel	O
,	O
which	O
has	O
a	O
wire	O
plugged	O
into	O
it	O
and	O
the	O
appropriate	O
Condition	O
selector	O
common	O
hub	O
to	O
be	O
tested	O
,	O
the	O
corresponding	O
two	O
Condition	O
selector	O
output	O
hubs	O
have	O
wires	O
plugged	O
into	O
them	O
and	O
the	O
Program	O
entry	O
hubs	O
specifying	O
the	O
instructions	B-General_Concept
to	O
jump	O
to	O
or	O
the	O
Program	O
advance	O
hub	O
to	O
continue	O
in	O
sequence	O
.	O
</s>
<s>
Complicated	O
conditions	O
involving	O
many	O
Condition	O
selectors	O
could	O
be	O
wired	O
to	O
execute	O
in	O
a	O
single	O
instruction	O
(	O
e.g.	O
,	O
Testing	O
the	O
sign	O
and	O
zero	O
states	O
of	O
multiple	O
accumulators	B-General_Concept
)	O
,	O
with	O
one	O
of	O
several	O
Program	O
entry	O
hubs	O
activated	O
.	O
</s>
<s>
Multi-way	O
jump	O
the	O
destination	O
track	O
(	O
T2	O
field	O
)	O
is	O
set	O
to	O
-	O
and	O
the	O
appropriate	O
Character	O
selector	O
hubs	O
on	O
the	O
control	O
panel	O
have	O
wires	O
plugged	O
into	O
them	O
and	O
the	O
Program	O
entry	O
hubs	O
specifying	O
the	O
instructions	B-General_Concept
to	O
jump	O
to	O
or	O
the	O
Program	O
advance	O
hub	O
to	O
continue	O
in	O
sequence	O
.	O
</s>
<s>
Certain	O
instructions	B-General_Concept
though	O
took	O
far	O
longer	O
than	O
the	O
typical	O
30ms	O
to	O
50ms	O
.	O
</s>
<s>
Input/Output	O
instructions	B-General_Concept
could	O
interlock	O
the	O
processor	O
for	O
as	O
many	O
revolutions	O
of	O
the	O
drum	O
as	O
needed	O
by	O
the	O
hardware	O
.	O
</s>
