<s>
Digital	O
Equipment	O
Corporation	O
's	O
RK05	B-Device
is	O
a	O
disk	B-Device
drive	I-Device
whose	O
removable	O
disk	B-Operating_System
pack	I-Operating_System
can	O
hold	O
about	O
2.5	O
megabytes	O
of	O
data	O
.	O
</s>
<s>
Introduced	O
1972	O
,	O
it	O
is	O
similar	O
to	O
IBM	O
's	O
1964-introduced	O
2310	B-Device
,	O
and	O
uses	O
a	O
disk	B-Operating_System
pack	I-Operating_System
similar	O
to	O
IBM	O
's	O
2315	O
disk	B-Operating_System
pack	I-Operating_System
,	O
although	O
the	O
latter	O
only	O
held	O
1	O
megabyte	O
.	O
</s>
<s>
An	O
RK04	B-Device
drive	O
,	O
which	O
has	O
half	O
the	O
capacity	O
of	O
an	O
RK05	B-Device
,	O
was	O
also	O
offered	O
.	O
</s>
<s>
Systems	O
on	O
which	O
it	O
can	O
be	O
used	O
include	O
DEC	O
's	O
PDP-8	B-Device
,	O
PDP-11	B-Device
,	O
and	O
PDP-15	B-Device
.	O
</s>
<s>
The	O
RK05	B-Device
was	O
a	O
moving	O
head	O
magnetic	B-Architecture
disk	I-Architecture
drive	O
manufactured	O
by	O
DEC	O
.	O
</s>
<s>
It	O
stored	O
approximately	O
2.5	O
MB	O
on	O
a	O
14	O
"	O
,	O
single-platter	O
IBM-2315-style	O
front-loading	O
removable	O
disk	B-Device
cartridge	O
.	O
</s>
<s>
The	O
PDP	B-Device
systems	O
to	O
which	O
it	O
could	O
be	O
attached	O
had	O
numerous	O
operating	O
systems	O
for	O
each	O
computer	O
architecture	O
,	O
so	O
by	O
changing	O
disk	B-Operating_System
pack	I-Operating_System
another	O
operating	O
system	O
could	O
also	O
be	O
booted	O
.	O
</s>
<s>
unlike	O
DECtape	O
,	O
the	O
RK05	B-Device
provided	O
personal	O
,	O
portable	O
,	O
and	O
expandable	O
storage	O
.	O
</s>
<s>
Although	O
a	O
minimal	O
PDP-8/A	O
came	O
with	O
only	O
one	O
drive	O
,	O
most	O
computers	O
were	O
configured	O
with	O
at	O
least	O
one	O
additional	O
storage	O
device	O
;	O
some	O
systems	O
had	O
four	O
drives	O
.	O
</s>
<s>
Occupying	O
10.5inches	O
(	O
6U	O
)	O
of	O
space	O
in	O
a	O
standard	O
19-inch	B-Application
rack	I-Application
,	O
the	O
drive	O
was	O
competitive	O
at	O
the	O
time	O
.	O
</s>
<s>
The	O
two	O
ferrite	O
and	O
ceramic	O
read/write	B-Device
heads	I-Device
were	O
pressed	O
towards	O
the	O
disk	B-Device
by	O
spring	O
arms	O
,	O
floating	O
on	O
an	O
air	O
bearing	O
maintained	O
by	O
the	O
rotation	O
of	O
the	O
disk	B-Device
.	O
</s>
<s>
They	O
were	O
positioned	O
by	O
a	O
voice	B-Device
coil	I-Device
actuator	O
using	O
a	O
linear	O
optical	O
encoder	O
for	O
feedback	O
.	O
</s>
<s>
When	O
used	O
on	O
16-bit	O
systems	O
such	O
as	O
the	O
PDP-11	B-Device
,	O
the	O
drive	O
stored	O
roughly	O
1.2	O
megawords	O
.	O
</s>
<s>
When	O
used	O
on	O
12-bit	O
systems	O
such	O
as	O
the	O
PDP-8	B-Device
,	O
the	O
drive	O
stored	O
1.6	O
megawords	O
(	O
so	O
roughly	O
the	O
same	O
bit	O
capacity	O
,	O
albeit	O
formatted	O
differently	O
)	O
.	O
</s>
<s>
Multiple	O
drives	O
were	O
daisy	B-Application
chained	I-Application
from	O
their	O
controller	O
using	O
Unibus	B-Device
cabling	O
;	O
a	O
terminator	O
was	O
installed	O
in	O
the	O
farthest	O
drive	O
.	O
</s>
<s>
The	O
16-bit	O
(	O
Unibus	B-Device
)	O
controller	O
was	O
known	O
as	O
the	O
RK11	B-Device
;	O
it	O
allowed	O
the	O
connection	O
of	O
up	O
to	O
eight	O
RK05	B-Device
drives	O
.	O
</s>
<s>
The	O
most-common	O
12-bit	O
(	O
Omnibus	O
)	O
controller	O
was	O
known	O
as	O
the	O
RK8E	B-Device
;	O
it	O
supported	O
up	O
to	O
four	O
RK05	B-Device
drives	O
.	O
</s>
<s>
The	O
RK05	B-Device
disk	B-Device
had	O
more	O
than	O
4096	O
sectors	O
and	O
so	O
could	O
not	O
be	O
addressed	O
completely	O
by	O
a	O
single	O
PDP-8	B-Device
12-bit	O
word	O
.	O
</s>
<s>
To	O
accommodate	O
this	O
,	O
the	O
OS/8	B-Operating_System
operating	O
system	O
split	O
each	O
drive	O
into	O
two	O
logical	O
volumes	O
,	O
for	O
example	O
,	O
RKA0	O
and	O
RKB0	O
,	O
representing	O
the	O
outermost	O
and	O
innermost	O
cylinders	O
of	O
the	O
drive	O
.	O
</s>
<s>
Prior	O
to	O
the	O
introduction	O
of	O
DEC	O
's	O
own	O
drives	O
,	O
DEC	O
resold	O
two	O
drives	O
from	O
Diablo	O
Data	O
Systems	O
(	O
later	O
acquired	O
by	O
Xerox	O
)	O
,	O
the	O
1.22	O
megabyte	O
RK02	B-Device
,	O
of	O
which	O
very	O
few	O
were	O
shipped	O
,	O
and	O
the	O
2.45	O
megabyte	O
RK03	B-Device
(	O
Diablo	O
Model	O
31	O
)	O
.	O
</s>
<s>
These	O
were	O
interface	O
compatible	O
with	O
the	O
RK05	B-Device
;	O
RK03	B-Device
and	O
RK05	B-Device
disks	B-Device
could	O
be	O
interchanged	O
as	O
well	O
.	O
</s>
<s>
The	O
RK04	B-Device
was	O
DEC	O
's	O
counterpart	O
to	O
the	O
RK02	B-Device
,	O
for	O
low-density	O
storage	O
of	O
600	O
Kwords	O
,	O
and	O
the	O
RK05	B-Device
was	O
DEC	O
's	O
counterpart	O
of	O
the	O
high-density	O
RK03	B-Device
,	O
storing	O
1.2	O
Mwords	O
.	O
</s>
<s>
The	O
RK05E	O
was	O
a	O
late	O
version	O
of	O
the	O
standard-density	O
RK05	B-Device
drive	O
.	O
</s>
<s>
The	O
RK05J	O
was	O
the	O
final	O
version	O
of	O
the	O
standard-density	O
RK05	B-Device
removable	O
pack	O
drive	O
.	O
</s>
<s>
By	O
"	O
fixing	O
"	O
the	O
otherwise	O
removable	O
cartridge	O
in	O
place	O
,	O
it	O
was	O
able	O
to	O
avoid	O
the	O
cartridge-to-cartridge	O
compatibility	O
problems	O
that	O
limited	O
the	O
capacity	O
of	O
the	O
ordinary	O
RK05	B-Device
.	O
</s>
<s>
RK05-compatible	O
non-DEC	O
RK05s	B-Device
were	O
produced	O
and	O
marketed	O
.	O
</s>
