Disk Pack Definition/Meaning:
A form of data storage medium consisting of an assembly of identical
14² diameter rigid magnetic disks that are mounted coaxially and equally
spaced. A similar nonrecording protective disk is fitted above the top recording
disk with another one below the bottom recording disk. The whole assembly is
rigidly clamped together, and is designed for dynamic stability at its intended
rotational speed on the disk drive, which can be up to 3600 revolutions per
minute. Disk packs are designed to be compatible with disk drives, mechanically and magnetically, and most types are the subjects of
international standards. The whole pack, when not mounted on the drive, is
contained within sealed plastic covers, in two parts, which help to ensure that
the pack is protected from damage, dust, and contamination. The bottom cover is
removed before mounting the pack on the drive; the top cover can only be removed
when the pack has been mounted.
The mechanical interface with the disk drive is
via an axial lockshaft in the pack, having a female thread engaging the male
spindle of the drive. On some types, a notch on the periphery of the bottom
protective disk is sensed by a transducer on the drive and signals the start of
each recording track. Additionally, a set of equispaced notches may be present
to signal the start of sectors within tracks; their presence and number depend
on the requirements of the drive controller. On other types, this information,
together with track spacing information, is prerecorded on a surface reserved
for this purpose, the servosurface.
Storage capacities range from 30 to 300
megabytes, over the range of track densities up to 400 tracks per inch,
recording densities up to 6000 bits per inch, and pack sizes of 5 to 12 disks.
Disk packs were introduced by IBM in 1963.
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