I wonder how the late generation paging disks (fixed head per track) like DG used in the 80's compared?
-----Original Message----- >From: Paul Koning via cctalk <cctalk@classiccmp.org> >Sent: May 10, 2018 7:29 AM >To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk@classiccmp.org> >Subject: how fast were drum memories? > >Drums were used as main memory in a number of early computers, and as >secondary memory for a while longer. I wonder how fast real ones (actually >constructed) managed to be. > >What prompted this question is reading an interesting document: >https://ir.cwi.nl/pub/9603 (in Dutch), "Principles of electronic calculating >machines, course notes February 1948" by Prof. A. van Wijngaarden at the >Mathematical Center (now CWI) in Amsterdam. It's quite a fascinating short >introduction into computing technology of that era. (One comment in the >intro: "The field is new. At the moment, the Eniac is the only working >machine..." -- probably not quite accurate given some classified machines, but >not too far wrong.) > >The section on main memory describes a bunch of different technoly >possibilities, one of them drum memory. He writes that a drum of 8 cm >diameter (a bit over 3 inches) and "a couple of decimeters height" could hold >maybe 100k bits, with a track pitch of "a few millimeters". So far so good. >He goes on to suggest that such a drum might spin at 1000 revolutions per >second, i.e., 60,000 rpm. That seems amazingly high. I could see it being >physically possible for a drum of only 40 mm radius, but it sure doesn't sound >easy. It's a good goal to strive for given that the logic, even in the days >of vacuum tubes, can run at cycle times of just a couple of microseconds. As >one more way to speed things up he suggests having multiple rows of read/write >heads, where the addressed word would be picked up by whichever head sees it >soonest. 10 rows and 60k rpm would give you 50 microseconds average access >time which "even for a parallel computer would be a very attractive number". >(Pages 17-18) > >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. > > paul >
