LGP-30 Memory Drum Update

Christian Corti cc at informatik.uni-stuttgart.de
Wed Jan 4 05:55:04 CST 2017

On Tue, 3 Jan 2017, Paul Koning wrote:
> The key questions for reconstructing such a device is what the 
> modulation scheme is, and the pulse pattern.  There might be marker 
> pulses for sector start, for example, or that might just be derived from 
> a counter in the controller.

It's in the maintenance manual. There is one flux change for a one bit, 
and a flux change to the opposite direction for a zero bit.
All timing is derived from the timing tracks S1..S3. The magic box to 
reconstruct these timing tracks must be synchronized to the base clock 
coming from the drum (137 kHz on European machines). The base clock is 
picked up with a special read head, the clock bits are "engraved" into the 
drum cylinder, so no need to write this clock track.


More information about the cctalk mailing list