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Metcalfe and Xerox - The Ethernet
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By
Mary
Bellis
In 1971, IBM introduced the first
"memory disk", as it was called then, or the "floppy
disk" as it is known today. The first floppy was an 8" plastic disk
coated with magnetic iron oxide; data was written to and read from the
disk's surface. The nickname "floppy" came from its flexibility. The floppy
disk was considered a revolutionary device at the time for it's portability
which provided a new and easy physical means of transporting data from
computer to computer.
The "floppy" was invented by IBM
engineers led by Alan Shugart. The first disks were designed for loading
microcodes into the controller of the Merlin (IBM 3330) disk pack file
(a 100 MB storage device). So, in effect, the first floppies were used
to fill another type of data storage device. Overnight, additional uses
for the floppy were discovered, making it the "new" program and file storage
medium.
How does a floppy work? It is a circle
of magnetic material similar to any kind of recording tape; one or two
sides of the disk are used for recording. The disk drive grabs the floppy
by its center and spins it like a record inside its housing. The read/write
head, much like the head on a tape deck, contacts the surface through an
opening in the plastic shell, or envelope. The Shugart floppy held 100
KBs of data.
In 1976, the 5 1/4" flexible disk
drive and diskette was developed by Alan Shugart for Wang Laboratories.
Wang had wanted a smaller floppy disk and drive to use with their desktop
computers. By 1978, more than 10 manufacturers were producing 5 1/4" floppy
drives.
In 1981, Sony introduced the first
3 1/2" floppy drives and diskettes. This is the floppy familiar to today's
computer user.
The following first hand information
was provided by Richard Mateosian who developed a floppy disk operating
system for the first "floppies".
The disks were 8 inches in diameter
and had a capacity of 200K, I think. Since they were so large (!) we divided
them into four partitions, each of which we regarded as a separate hardware
device -- analogous to a cassette drive (our other main peripheral storage
device). We used floppy disks and cassettes mostly as paper tape replacements,
but we also appreciated and exploited the random access nature of disks.
Our operating system had a set of
logical devices (source input, listing output, error output, binary output,
etc.) and a mechanism for establishing a correspondence between these and
the hardware devices. Our applications programs were versions of HP assemblers,
compilers, and so forth, modified (by us, with HP's blessing) to use our
logical devices for their I/O functions.
The rest of the operating system
was basically a command monitor. The commands had mainly to do with file
manipulation. There were some conditional commands (like IF DISK) for use
in batch files. The entire operating system and all of the application
programs were in HP 2100 series assembly language.
The underlying system software, which
we wrote from scratch, was interrupt driven, so we could support simultaneous
I/O operations, such as keying in commands while the printer was running
or typing ahead of the 10 character per second teletype. The structure
of the software evolved from Gary Hornbuckle's 1968 paper, a Multiprocessing
Monitor for Small Machines, and from PDP8-based systems, I worked on at
Berkeley Scientific Laboratories (BSL) in the late 1960s. The work at BSL
was largely inspired by the late Rudolph Langer, who improved significantly
on Hornbuckle's model. - Richard Mateosian Review Editor, IEEE Micro Berkeley,
CA
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Metcalfe and Xerox - The Ethernet
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