how fast were drum memories?

[Paul Koning]

> On May 10, 2018, at 10:57 AM, Chuck Guzis via cctalk <cctalk at classiccmp.org> wrote:
> 
> On 05/10/2018 07:29 AM, Paul Koning via cctalk wrote:
> 
>> I'm wondering what the reality of fast drum memories looked like, and whether anyone came even close to these numbers.  Also, am I right in thinking they are at least in principle achievable?  I know I could run the stress numbers, but haven't done so.
> 
> All of the STAR-100 stations, including the paging station used drums.
> 
> Jim Thornton and folks at CDC ADL were working on a 100K RPM drum
> spinning in vacuo for a paging store, but they couldn't get it to work
> reliably.   At any rate, STAR was the last system I saw fast drums on
> and you can check the figures in the Bitsavers documentation under
> cdc/cyber/cyber200.  At any rate, a head-per-track drum could be much
> faster than a disk.

Faster than a moving head disk, certainly, though head per track disks also existed.  DEC had some fast ones -- RS04 comes to mind.

I looked at the Star peripherals manual.  It describes the paging drum as a modified 865 drum, which "rotates at 1800 rpm".  So it might have a high transfer rate -- 12 bit words in parallel from 12 heads -- but clearly quite high latency.

	paul