Monthly Archives: August 2012

Identify It Challenge for 7-26-2012 Answer

Sorry for the delay in posting this, its been a very busy late summer for Harris Educational!  Mostly good stuff, but enough of that, on to the answer.

Here is the original video “Identify It Challenge” as posted on 7-26-2012

And now here is the answer:

Read/Write Head Assembly from Diablo Systems Series 30 Disk Drive

Read/Write Head Assembly from Diablo Systems Series 30 Disk Drive
Shown with late 1990’s Iomega Zip Disk for Comparison

This assembly is the read/write head from a Diablo Systems Series 30 Disk Drive manufactured around 1976.  The drive was not a traditional Hard Drive (or fixed disk) but instead took IBM 2315 disk cartridges that were about one foot in diameter and could hold a grand total of 1.25 MB!  (the later series 31 model used a disk that could hold 2.5 MB).   A photo of these disks can be found here.

The mechanism has a synchronous drive motor (with run capacitor) built into the bottom of its cast housing.  This motor drives a shaft with integral pinion gears that engage a rack gear that can move the drive’s double sided read/write heads back and forth along the disk surface.  The large solenoid and damper open and close the read/write head around the cartridge after it has been inserted into the drive.  The green marked disk on top  corresponds to the tracks on the disk itself and was used to mechanically orient the drive heads in order to synchronize them to a standard disk during manual alignment.  The green disk also contains a kind of rotational position sensor that sends pulses back to the controller based on its movement.  The micro-switches act as end-stops to keep the heads from being sent past their absolute physical end-stops.  The whole drive head assembly weighs in at about six and a half pounds.

You can see a pictures of the whole drive AND read about how it works through repair and maintenance manuals at the following links:

This drive (and two others) came into my possession around 1990.  My high school electronics lab received them as a junk donation much earlier in the mid 1980’s and they’d sit in storage taking up space until then.  My electronics teacher gave them to me when I helped him clean out the storage and I then dissected them to learn how they worked and for parts.  They were much too large and heavy for me to keep intact at the time, though I did keep the read/write mechanism intact knowing that one day it might come in handy for some kind of display, and sure enough it fits into the Identify It Challenge nicely!

This assembly (or rather the disk drive that it came from) has some significance in the history of computing because:

  • It is a predecessor to the Floppy Drive
  • It helped to show the value of removable random access storage (not just linear access storage like tape)
  • It was a peripheral for mini-computers and as such was an add on (not necessarily manufactured by the mini-computer maker) and as such helped to bring in the idea of standards and interchangeability.
  • It was used as storage for the Xerox Parc computer, the first computer with a graphical user interface and a predecessor to modern PC’s

Thanks to everyone who made guesses over on Facebook.  The  first person to make a correct guess was Duffy Toler, guessing it was a read/write head assembly.  John Sucilla came closer by guessing it was from a DEC RK-05 disk drive.  (in reality Diablo Systems was bought out and became a part of Xerox and then later Xerox sold these drives to Digital Equipment Corporation where they were used as peripherals for their PDP line of computers.)

Stay Tuned for the Next Identify It Challenge!