how fast were drum memories?

Mike Loewen mloewen at
Thu May 10 15:46:36 CDT 2018

On Thu, 10 May 2018, Al Kossow via cctalk wrote:

> On 5/10/18 10:37 AM, Al Kossow via cctalk wrote:
>> On 5/10/18 9:29 AM, Paul Koning via cctalk wrote:
>>> One that comes to mind is the DEC RS04.  It spins at roughly 3600 rpm (a hair less, so obviously a 2 pole induction motor running off 3-phase 60 Hz power).
>> Vermont Research drums (model 1175B) spun at 3450 rpm 3ph 220v, The HP 2773 on the 2000A TSB was from VR so I expect RPM
>> would be similar for most drums of similar diameter.
> Just checked, and the LGP-30 and RPC-4000 drums are both listed as 3600 rpm

    The drums on the SAGE system (12 on each side), are listed as follows:

Diameter: 	10.7"
Width:	  	12.5"
Weight:	  	105 lbs (cylinder, only), 450 lbs for entire drum assembly
Speed:	  	2914 rpm
Heads:	  	Up to 12 R/W bars, with up to 40 heads on each bar, 1 erase bar
 		6 pairs, one for Compuuter-to-Drum (CD), one for
 		Other-than-computer-to-Drum (OD)
 		Head spacing 0.3" apart on each bar
Drum Layout:	2048 registers on 33 channels (tracks), 6 fields
 		Channel spacing is 0.050"
Access Time:	Maximum 20ms, average 10ms
Write Current:	110ma

    The R/W bars are arranged in pairs (CD and OD) so that I/O devices can 
access the drum independently of the computer.

    More than you ever wanted to know about SAGE drums (thanks, Al!):

    Here's one of the earlier style R/W heads:

Mike Loewen				mloewen at
Old Technology

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