Monday, June 11, 2007

Floppy disks

In the early micro days we used cassette tapes and floppy disks. Floppies were better for many reasons but they were expensive. The Apple Disk II drives were $495 including the controller. Once you had one of these babies you still needed floppy disks. I remember pretty clearly in the early 80's spending $80 for a box of 10 floppy disks. These were Dysan disks, and were of very good quality.

However these disks probably exceeded the quality required. Later on some less expensive floppy disks became available from the likes of Maxell and memorably named Elephant Memory Systems. These were $2.50 or so per disk. The disk surfaces weren't as polished, and some cheap brands didn't have a reinforced mount but no matter really. The cheap disks were pretty much as reliable as far as anybody could tell.

Disk drive systems themselves were all quite different from each other. Apple's legendary Steve Wozniak had managed to create the ultimate in economy of design for a disk controller with a small card having only 5 ICs. Most other disk controllers were long circuitboards with 2 to 3 dozen chips. Monsters. ;-)

Some of these floppy drives used hard sector disks, meaning that there was an index hole in the media for each sector on the disk. So, if the disk was meant for a 16 sector drive, the disk would have 16 timing holes cut out of it evenly around the inner part of the disk. This would be read by an LED and a sensor. The Apple II used soft sector disks where there was only one hole cut in the disk, and the drive controller itself decided how many sectors to put on the disk by doing careful timing.

I remember that my father's H-89 had hard sector disks. The drives also made a strange clunking noise as they operated. The Apple II's drives made the much more familiar brrrr, brrr, mmm, mmm sound of most floppy drives and they were faster than the H-89 drives.


Carlo Dossi said...

And the 8-inch, hard sectored disks? If I remind correctly, I used them to write my Ph.D. thesis with Wordstar on a CP/M Z-80 machine.
Thinking of Z-80, I must tell you that it is still alive as embedded microprocessor on an Amel polarograph I am bringing to a new life; as I already told you, I am writing a complete software package in Liberty Basic to drive it thru the RS232 port.

Yours Carlo

Ray said...

The H-89 used floppies with 10
hard sectors. The clunk you
refer to was the "head load"
solenoid engaging. This released a
spring-loaded pad against
the back side of the disk to press
it against the head. Those were
Perkin-Elmer/Wangco drives.
Most other drive makes just had
the head "loaded" all
the time it was in the drive, wearing out the disks much faster.

A thunk-and-release for each
sector access was annoying, but
a later driver upgrade added a time-out on the head load so that
reads in close succession would
only load once and stay loaded
until the end.