<s>
The	O
IBM	B-Device
3850	I-Device
Mass	I-Device
Storage	I-Device
System	I-Device
(	O
MSS	O
)	O
was	O
an	O
online	O
tape	B-Device
library	I-Device
used	O
to	O
hold	O
large	O
amounts	O
of	O
infrequently	O
accessed	O
data	O
.	O
</s>
<s>
It	O
was	O
one	O
of	O
the	O
earliest	O
examples	O
of	O
nearline	B-General_Concept
storage	I-General_Concept
.	O
</s>
<s>
Starting	O
in	O
the	O
late-1960s	O
IBM	O
's	O
lab	O
in	O
Boulder	O
,	O
Colorado	O
began	O
development	O
of	O
a	O
low-cost	O
mass	B-Device
storage	I-Device
system	I-Device
based	O
on	O
magnetic	O
tape	B-Architecture
cartridges	O
.	O
</s>
<s>
Originally	O
the	O
system	O
was	O
going	O
to	O
be	O
used	O
as	O
a	O
directly	O
attached	O
memory	O
device	O
,	O
but	O
as	O
the	O
speed	O
of	O
computers	O
grew	O
in	O
relation	O
to	O
the	O
storage	O
,	O
the	O
product	O
was	O
re-purposed	O
as	O
an	O
automated	O
system	O
that	O
would	O
offload	O
little-used	O
data	O
from	O
hard	B-Device
disk	I-Device
systems	O
.	O
</s>
<s>
Known	O
internally	O
as	O
Comanche	O
while	O
under	O
development	O
,	O
IBM	O
management	O
found	O
a	O
number	O
of	O
niche	O
uses	O
for	O
the	O
concept	O
,	O
and	O
announced	O
it	O
officially	O
as	O
the	O
IBM	B-Device
3850	I-Device
on	O
October	O
9	O
,	O
1974	O
.	O
</s>
<s>
After	O
more	O
than	O
a	O
decade	O
(	O
comparable	O
to	O
the	O
IBM	B-Device
2321	I-Device
Data	I-Device
Cell	I-Device
,	O
1964	O
–	O
1975	O
)	O
,	O
it	O
was	O
withdrawn	O
August	O
5	O
,	O
1986	O
.	O
</s>
<s>
The	O
Mass	B-Device
Storage	I-Device
System	I-Device
consisted	O
of	O
a	O
library	O
of	O
cylindrical	O
plastic	O
cartridges	O
,	O
two	O
inches	O
wide	O
and	O
long	O
,	O
each	O
holding	O
a	O
spool	O
of	O
tape	B-Architecture
long	O
storing	O
50MB	O
;	O
each	O
virtual	O
disk	O
required	O
a	O
pair	O
of	O
cartridges	O
.	O
</s>
<s>
The	O
data	O
were	O
accessed	O
via	O
virtual	O
IBM	B-Device
3330	I-Device
disk	O
drives	O
,	O
and	O
physically	O
cached	O
on	O
a	O
combination	O
of	O
3330	O
and	O
3350	O
staging	O
drives	O
,	O
the	O
data	O
being	O
transferred	O
automatically	O
between	O
cartridge	O
and	O
disk	O
drive	O
in	O
processes	O
called	O
staging	O
and	O
destaging	O
.	O
</s>
<s>
Stage	O
time	O
for	O
data	O
from	O
cartridge	O
to	O
disk	O
was	O
typically	O
15	O
seconds	O
,	O
including	O
about	O
two	O
seconds	O
to	O
move	O
the	O
cartridge	O
into	O
a	O
read	O
station	O
,	O
and	O
eight	O
to	O
ten	O
seconds	O
to	O
read	O
the	O
200-foot	O
tape	B-Architecture
.	O
</s>
<s>
The	O
drive	O
pulled	O
the	O
tape	B-Architecture
from	O
the	O
cartridge	O
and	O
wound	O
it	O
once	O
around	O
a	O
cylindrical	O
mandrel	O
in	O
a	O
helix	B-Application
,	O
then	O
stopped	O
the	O
tape	B-Architecture
.	O
</s>
<s>
Then	O
drive	O
then	O
wound	O
the	O
tape	B-Architecture
a	O
small	O
step	O
forward	O
and	O
the	O
head	O
rotated	O
to	O
do	O
the	O
next	O
track	O
.	O
</s>
<s>
Depending	O
on	O
technical	O
definitions	O
this	O
might	O
be	O
even	O
considered	O
a	O
first	O
example	O
of	O
a	O
digital	O
helical	O
scan	O
recording	O
,	O
long	O
before	O
Exabyte	B-Device
's	I-Device
helical	I-Device
drive	I-Device
(	O
which	O
was	O
based	O
on	O
analog	O
video	O
helical	O
recording	O
systems	O
developed	O
earlier	O
)	O
.	O
</s>
<s>
When	O
free	O
disk	O
space	O
was	O
required	O
a	O
group	O
of	O
cylinders	O
were	O
selected	O
to	O
be	O
destaged	O
to	O
tape	B-Architecture
,	O
these	O
were	O
transferred	O
with	O
minimal	O
or	O
no	O
change	O
of	O
format	O
.	O
</s>
<s>
Each	O
tape	B-Architecture
could	O
store	O
202	O
cylinder	O
images	O
of	O
19	O
tracks	O
each	O
,	O
half	O
of	O
the	O
404	O
cylinders	O
in	O
a	O
3330	O
disk	O
pack	O
.	O
</s>
<s>
Cylinder	O
locations	O
on	O
the	O
tape	B-Architecture
were	O
fixed	O
and	O
identified	O
by	O
markers	O
along	O
the	O
edge	O
.	O
</s>
