IBM 3350 Direct
Access Storage
- Models A2, A2F, B2 & B2F announced July 15,
1975 and withdrawn September 5, 1994
- Models C2 and C2F announced November 4, 1975 and
withdrawn September 5, 1994
Known during its development as "Madrid,"
the IBM 3350 was introduced in 1975 and first delivered
the following year. It extended Winchester
technology by increasing the number of disks per
drive and the recording density to provide a 4.5 times
increase in capacity per spindle. In addition, the developers
eliminated the customer-removable disk pack and circled
back to fixed disks, as in the IBM
RAMAC, to achieve higher recording densities and
lower cost per bit of online storage. In addition, the
elimination of operator handling -- and exposure to
external contamination -- provided high reliability.
The 3350 furnished a maximum storage capacity of approximately
317.5MB per drive (635MB per unit), allowing more than
2.5 billion bytes of online storage per 3350 string.
The data rate was 1198K/second and average seek time
was 25 milliseconds.
The 3350 Models A2F and B2F provided 1,144,140 bytes
of zero seek time storage per spindle (2,288,280 per
unit) when operating in 3350 native mode. Models A2
and A2F were two-drive units with associated controls,
which attached to the IBM System/370 Models 135, 155-II
and 165-II via the 3830 Model 2, and to the IBM System/370
Model 145, 158 and 168 via their ISCs and/or the 3830
Model 2. The 3350 Models B2 and B2F were two-drive units
which attached to the 3350 Model A2 or A2F. Up to three
B2 or B2F units could be attached to each A2 or A2F
unit, for a maximum of eight drives per 3350 string.
Characteristics
|
|
| |
|
| Average seek time (ms): |
25 |
| Average rotational delay (ms): |
8.4 |
| Data Rate (KB/sec.): |
1198 |
| Bytes per track: |
19,069 |
| Tracks per logical cylinder: |
30 |
| Logical cylinders per drive: |
555 |
| Capacity per drive (MB) approx. |
317.5 |
Features
- Rotational position sensing, which permitted improved
block multiplexer channel utilization.
- Error correction of single data error bursts of
up to four bits.
- Command retry, which enabled the storage control
to recover from certain subsystem errors without recourse
to system error recovery procedures.
- Read only switch, gave increased data security
by providing for each drive the means to protect data
from being overwritten or erased.
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