Homebrew Drum Computer (magnetic heads)

[Mike Loewen]

On Fri, 14 Dec 2007, jim s wrote:

> Also all the drums I ever saw had a sort of flying head with a horizontal 
> head in a hole with a small spring mechanism that would hold it in position. 
> I don't if the head normally was out of contact with the drum while the head 
> was stopped and was then sucked in, or if it landed and was pushed back, but 
> that whole affair was delicate as well.

    Just for reference, here's some information about the drums used in the 
SAGE (AN/FSQ-7) system:

Length: 12.6 inches
Diameter: 10.7 inches
Weight: 85 lbs
Speed: 2914 RPM
Recording Surface: nickel-cobalt alloy
Word Length: 32 bits (typically, plus various control and parity bits)

    The heads were fixed, on 6 pairs of mounting bars, with a critical air 
gap between the head the drum surface.  The Q7 drums had two sets of 
heads to support simultaneous r/w operations between the computer and 
drums, and outside equipment (radar info, xtel, etc).

    Here's a picture from the Computer History Museum:

http://sturgeon.css.psu.edu/~mloewen/Q7/CHDrum.jpg

    ... and a very small picture of r/w head:

http://sturgeon.css.psu.edu/~mloewen/Q7/parts.gif

    The head is in the lower right hand corner.

    Specifics were taken from pp 125-131 of the "Theory of Programming" 
T.O.:

http://www.bitsavers.org/pdf/ibm/sage/31P2-2FSQ7-112_SagePgmNov56.pdf


Mike Loewen				mloewen at cpumagic.scol.pa.us
Old Technology	http://sturgeon.css.psu.edu/~mloewen/Oldtech/