of Microprocessors

MICROPROCESSORS 143
that was quickly reduced to 8 inches and later to 5 inches. With each size
reduction, the typical capacity range remained about the same, which means
that the bit and track density figures of current 5-inch units are truly
remarkable.
Today, miniature 5-inch Winchester disk drives (sometimes called
"mini-winnies") are fairly common on high-end microcomputers. The most
popular capacities are 5 and 10M bytes on one and two sides, respectively, of
a single platter, and the data transfter rate is typically 625K bytes/sec.
Greater capacities up to 40M bytes are possible by stacking up additional
platters, while experimental units have attained up to 160M bytes by
increasing the bit and track density. Although the 5- and 10M-byte drive
prices have gradually declined to under $500, the real impetus to their
increased use was availability of controller ICs. Prior to that, a rigid disk
controller board might have 50-100 IC packages and could easily cost in
excess of $1,000.
One fundamental problem with any kind of Winchester disk drive is
that the recording medium is fixed in place within the drive. Archiving and
keeping backup copies of data (in case of computer or disk drive failure)
required that it be read off the Winchester disk and rewritten onto a
different, removable medium. Although special cartridge tape drives are
often promoted for this purpose, in most cases the floppy disk drive (which
still must be present to get new software loaded into the machine) is used
instead. Another problem is that when the application fills up the
Winchester disk, one does not have the option of just changing the medium
and continuing; another drive or a capacity upgrade is necessary. Attempts
have been made to retain the high bit and track densities of Winchester
technology while offering removable media and still keeping the cost
reasonable. After several false starts, it appears that this goal will ultimately
be reached.
One unique approach that is creating quite a bit of interest is "Bernouli
technology" pioneered by IoMega Corporation. The floppy medium is fixed
to a simple metal hub and packaged in a rigid plastic case. When inserted
into the drive, the disk is spun at high speed, typically 1,500 rpm, which
makes it rigid due to centrifugal force. The speed is also high enough to
make the disk pull toward yet float over the head on an air cushion (Bernouli
effect). The real advantage is that momentary contact between the disk and
head (called a "crash" in rigid disk terminology) is not detrimental, which
makes the units rugged and reliable. Problems with dimensional stability of
the medium are solved by using a servo positioner (rather than stepping
motor), which does tend to increase the drive cost. The removable cartridges,
however, are potentially very inexpensive. This feature makes a Bernouli
technology system very attractive in direct computer synthesis applications in
which the media cost for storing digitized audio data must be minimized.