<s>
Drum	B-General_Concept
memory	I-General_Concept
was	O
a	O
magnetic	O
data	B-General_Concept
storage	I-General_Concept
device	I-General_Concept
invented	O
by	O
Gustav	O
Tauschek	O
in	O
1932	O
in	O
Austria	O
.	O
</s>
<s>
Drums	O
were	O
widely	O
used	O
in	O
the	O
1950s	O
and	O
into	O
the	O
1960s	O
as	O
computer	B-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
Many	O
early	O
computers	O
,	O
called	O
drum	O
computers	O
or	O
drum	O
machines	O
,	O
used	O
drum	B-General_Concept
memory	I-General_Concept
as	O
the	O
main	O
working	O
memory	O
of	O
the	O
computer	O
.	O
</s>
<s>
Some	O
drums	O
were	O
also	O
used	O
as	O
secondary	O
storage	O
as	O
for	O
example	O
various	O
IBM	O
drum	B-General_Concept
storage	I-General_Concept
drives	O
.	O
</s>
<s>
Drums	O
were	O
displaced	O
as	O
primary	O
computer	B-General_Concept
memory	I-General_Concept
by	O
magnetic	O
core	B-General_Concept
memory	I-General_Concept
,	O
which	O
offered	O
a	O
better	O
balance	O
of	O
size	O
,	O
speed	O
,	O
cost	O
,	O
reliability	O
and	O
potential	O
for	O
further	O
improvements	O
.	O
</s>
<s>
Drums	O
in	O
turn	O
were	O
replaced	O
by	O
hard	B-Device
disk	I-Device
drives	I-Device
for	O
secondary	O
storage	O
,	O
which	O
were	O
both	O
less	O
expensive	O
and	O
offered	O
denser	O
storage	O
.	O
</s>
<s>
A	O
drum	B-General_Concept
memory	I-General_Concept
or	O
drum	B-General_Concept
storage	I-General_Concept
unit	O
contained	O
a	O
large	O
metal	O
cylinder	O
,	O
coated	O
on	O
the	O
outside	O
surface	O
with	O
a	O
ferromagnetic	O
recording	O
material	O
.	O
</s>
<s>
It	O
could	O
be	O
considered	O
the	O
precursor	O
to	O
the	O
hard	B-Device
disk	I-Device
drive	I-Device
(	O
HDD	O
)	O
,	O
but	O
in	O
the	O
form	O
of	O
a	O
drum	O
(	O
cylinder	O
)	O
rather	O
than	O
a	O
flat	O
disk	O
.	O
</s>
<s>
In	O
most	O
designs	O
,	O
one	O
or	O
more	O
rows	O
of	O
fixed	O
read-write	B-Device
heads	I-Device
ran	O
along	O
the	O
long	O
axis	O
of	O
the	O
drum	O
,	O
one	O
for	O
each	O
track	O
.	O
</s>
<s>
Some	O
,	O
such	O
as	O
the	O
English	B-Device
Electric	I-Device
DEUCE	I-Device
drum	O
and	O
the	O
UNIVAC	B-Device
FASTRAND	I-Device
had	O
multiple	O
heads	O
moving	O
a	O
short	O
distance	O
on	O
the	O
drum	O
in	O
contrast	O
to	O
modern	O
HDDs	O
,	O
which	O
have	O
one	O
head	O
per	O
platter	O
surface	O
.	O
</s>
<s>
Magnetic	B-General_Concept
drum	I-General_Concept
units	O
used	O
as	O
primary	O
memory	O
were	O
addressed	O
by	O
word	O
.	O
</s>
<s>
This	O
method	O
of	O
timing-compensation	O
,	O
called	O
the	O
"	O
skip	B-Application
factor	I-Application
"	O
or	O
"	O
interleaving	B-Application
"	O
,	O
was	O
used	O
for	O
many	O
years	O
in	O
storage	O
memory	O
controllers	O
.	O
</s>
<s>
Tauschek	O
's	O
original	O
drum	B-General_Concept
memory	I-General_Concept
(	O
1932	O
)	O
had	O
a	O
capacity	O
of	O
about	O
500,000	O
bits	O
(	O
62.5	O
kilobytes	O
)	O
.	O
</s>
<s>
One	O
of	O
the	O
earliest	O
functioning	O
computers	O
to	O
employ	O
drum	B-General_Concept
memory	I-General_Concept
was	O
the	B-Device
Atanasoff	I-Device
–	I-Device
Berry	I-Device
computer	I-Device
(	O
1942	O
)	O
.	O
</s>
<s>
Magnetic	B-General_Concept
drums	I-General_Concept
were	O
developed	O
for	O
the	O
U.S.	O
Navy	O
during	O
World	O
War	O
II	O
with	O
the	O
work	O
continuing	O
at	O
Engineering	O
Research	O
Associates	O
(	O
ERA	O
)	O
in	O
1946	O
and	O
1947	O
.	O
</s>
<s>
Other	O
early	O
drum	B-General_Concept
storage	I-General_Concept
device	O
development	O
occurred	O
at	O
Birkbeck	O
College	O
(	O
University	O
of	O
London	O
)	O
,	O
Harvard	O
University	O
,	O
IBM	O
and	O
the	O
University	O
of	O
Manchester	O
.	O
</s>
<s>
The	O
first	O
mass-produced	O
computer	O
,	O
the	O
IBM	O
650	O
,	O
initially	O
had	O
up	O
to	O
2,000	O
10-digit	O
words	O
,	O
about	O
17.5	O
kilobytes	O
,	O
of	O
drum	B-General_Concept
memory	I-General_Concept
(	O
later	O
doubled	O
to	O
4,000	O
words	O
,	O
about	O
35	O
kilobytes	O
,	O
in	O
the	O
Model	O
4	O
)	O
.	O
</s>
<s>
As	O
late	O
as	O
1980	O
,	O
PDP-11/45	B-Device
machines	O
using	O
magnetic	O
core	O
main	O
memory	O
and	O
drums	O
for	O
swapping	O
were	O
still	O
in	O
use	O
at	O
many	O
of	O
the	O
original	O
UNIX	B-Application
sites	O
.	O
</s>
<s>
In	O
BSD	B-Operating_System
Unix	I-Operating_System
and	O
its	O
descendants	O
,	O
was	O
the	O
name	O
of	O
the	O
default	O
virtual	B-Architecture
memory	I-Architecture
(	O
swap	O
)	O
device	O
,	O
deriving	O
from	O
the	O
use	O
of	O
drum	O
secondary-storage	O
devices	O
as	O
backup	O
storage	O
for	O
pages	B-General_Concept
in	O
virtual	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
Magnetic	B-General_Concept
drum	I-General_Concept
memory	I-General_Concept
units	O
were	O
used	O
in	O
the	O
Minuteman	O
ICBM	O
launch	O
control	O
centers	O
from	O
the	O
beginning	O
in	O
the	O
early	O
1960s	O
until	O
the	O
REACT	O
upgrades	O
in	O
the	O
mid-1990s	O
.	O
</s>
