<s>
RL01	B-Device
and	O
RL02	B-Device
drives	O
are	O
moving	O
head	O
magnetic	B-Architecture
disk	I-Architecture
drives	O
manufactured	O
by	O
Digital	O
Equipment	O
Corporation	O
for	O
the	O
PDP-8	B-Device
and	O
PDP-11	B-Device
microcomputers	O
.	O
</s>
<s>
The	O
RL01	B-Device
and	O
RL02	B-Device
drives	O
stored	O
approximate	O
5MB	O
and	O
10MB	O
respectively	O
,	O
utilizing	O
a	O
removable	O
data	O
cartridge	O
.	O
</s>
<s>
Up	O
to	O
four	O
RL02	B-Device
or	O
RL01	B-Device
drives	O
may	O
be	O
used	O
,	O
in	O
any	O
combination	O
,	O
from	O
a	O
single	O
controller	O
.	O
</s>
<s>
Typically	O
an	O
RL11	O
in	O
the	O
case	O
of	O
a	O
Unibus	O
PDP-11	B-Device
and	O
an	O
RLV11	O
or	O
RLV12	O
in	O
the	O
case	O
of	O
a	O
Q-bus	O
PDP-11	B-Device
.	O
</s>
<s>
On	O
the	O
PDP-8/a	O
the	O
controller	O
is	O
an	O
RL8A	O
which	O
consists	O
of	O
an	O
M8433	O
Hex	O
wide	O
Omnibus	O
card	O
.	O
</s>
<s>
The	O
RL01	B-Device
and	O
RL02	B-Device
data	O
cartridges	O
are	O
based	O
on	O
IBM	O
5440	O
cartridges	O
,	O
but	O
have	O
servo	O
tracking	O
data	O
pre-encoded	O
onto	O
the	O
cartridge	O
.	O
</s>
<s>
This	O
reduces	O
the	O
need	O
for	O
strict	O
head	O
alignment	O
,	O
allowing	O
cartridges	O
to	O
be	O
used	O
in	O
several	O
drives	O
(	O
although	O
there	O
was	O
no	O
backwards	O
compatibility	O
between	O
RL02	B-Device
and	O
RL01	B-Device
cartridges	O
,	O
despite	O
similar	O
appearance	O
)	O
.	O
</s>
<s>
RL01	B-Device
cartridges	O
have	O
256	O
tracks	O
,	O
and	O
RL02	B-Device
cartridges	O
have	O
512	O
tracks	O
.	O
</s>
<s>
On	O
both	O
RL01	B-Device
and	O
RL02	B-Device
cartridges	O
,	O
each	O
track	O
is	O
divided	O
into	O
40	O
sectors	O
of	O
equal	O
length	O
.	O
</s>
<s>
Data	O
is	O
encoded	O
on	O
the	O
disk	O
using	O
Modified	B-Protocol
Frequency	I-Protocol
Modulation	I-Protocol
,	O
where	O
a	O
one	O
bit	O
will	O
result	O
in	O
a	O
magnetic	O
flux	O
reversal	O
on	O
the	O
magnetic	O
coating	O
of	O
the	O
cartridge	O
.	O
</s>
<s>
The	O
last	O
track	O
of	O
an	O
RL01	B-Device
and	O
RL02	B-Device
cartridge	O
contains	O
a	O
table	O
which	O
lists	O
all	O
of	O
the	O
bad	O
sectors	O
on	O
the	O
cartridge	O
.	O
</s>
<s>
This	O
data	O
should	O
be	O
encoded	O
in	O
Modified	B-Protocol
Frequency	I-Protocol
Modulation	I-Protocol
,	O
as	O
the	O
drive	O
does	O
not	O
encode	O
or	O
decode	O
this	O
data.System	O
ClockThe	O
system	O
clock	O
shifts	O
data	O
through	O
the	O
Drive	O
Command	O
line	O
and	O
also	O
provides	O
a	O
reference	O
for	O
the	O
disk	O
servo	O
motor	O
.	O
</s>
