Back to DASD.
The oldest disk drive artifact we have in the collection is a read/write head from an IBM 2311 disk drive.
This is NOT a 2311 disk drive, it is a 1312 disk drive, but very similar.
You can see the disk pack under the cover which opened upwards.
The nice thing about this disk drive is that you can see the heads moving.
This was useful because when your program was running,
reading data from one file (they were called datasets in those days),
and writing it to another,
if the heads moved between the centre and outer edge of the disk,
you could change the position of the files physically closer to each other
so that the heads had much less distance to move,
so your program ran much faster.
|Mus.Cat. NEWUC:2004.25||Mnfctr: IBM||Date: 1964||Ser. No: 439161||Model: -|
|Comp: Disk Read/Write Head||Length: 123mm||Width: 23mm||Depth: 6mm||Weight: 18g|
This is the read/write head assemby. Each disk pack contained six 14-inch diameter disks.
So there was twelve surfaces, each having a single read/write head.
The twelve arms were connected together like tines of a fork and the read/write heads floated above
the surfaces on a boundary layer of air being dragged round by the disk.
Wherever the head assembly stopped each head flew over a circle, this circle is called a track.
So when the head assembly stopped moving it was over twelve tracks.
Each could be accessed without moving head assembly simply by electronically selecting one of the welve.
These twelve tracks were called a cylinder. So information was written in cylinders of 12 tracks
before the read/write head had to be moved which took a long time, milliseconds instead of microseconds.
A close-up of the head itself shows it is made of metal with a curved leading edge.
The curve trapped the boundary layer of air attached to the disk sweeping it under the head.
The head was mounted on a stainless steel gimbal that allowed it to 'fly' over the surface of the disk.
The two holes assist aerodynamic stability, and the centre rectangle is the gap between the poles
of the magnet. A winding (unseen), around the magnet had an electric current that was controlled to
produce a magnetic field, one way or the other, that could write a magnetic pattern on the disk that
was the data to be recorded.
Reading involved sensing the current induced in the winding as the magnet passed over a pattern.
That is a millimeter scale on the right hand side.
There is a wonderful amount of information about this disk drive at: