10 May
2018
10 May
'18
7:37 a.m.
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 at
classiccmp.org>
Sent: May 10, 2018 7:29 AM
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
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
10 May
10 May
7:48 a.m.
There are two places I'd check. The manual for the Royal McBee LGP-30 and
the book Computer Structures: Readings and Examples by G Bell et al.
Bill
On Thu, May 10, 2018 at 10:37 AM, Grif via cctalk <cctalk at classiccmp.org>
wrote:
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 at
classiccmp.org>
Sent: May 10, 2018 7:29 AM
To: "General Discussion: On-Topic and Off-Topic Posts" <
cctalk at
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
9:29 a.m.
On May 10, 2018, at 10:37 AM, Grif <grif615 at
mindspring.com> wrote:
I wonder how the late generation paging disks (fixed head per track) like DG used in the
80's compared?
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). Transfer rate is 0.5
megabytes per second, but still, at that RPM, average latency is 8.5 ms.
paul
10:37 a.m.
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.
10:39 a.m.
there is a picture of a small 10K RPM drum here
http://museum.ipsj.or.jp/en/computer/device/magnetic_drum/0017.html
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.
from
https://ia800809.us.archive.org/27/items/TNM_Drum_memories_-_Vermont_Resear…
12:01 p.m.
On 5/10/18 10:37 AM, Al Kossow via cctalk wrote:
On 5/10/18 9:29 AM, Paul Koning via cctalk wrote:
Just checked, and the LGP-30 and RPC-4000 drums are both listed as 3600 rpm
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. 
12:05 p.m.
On 2018-05-10 4:01 PM, Al Kossow via cctalk wrote:
On 5/10/18 10:37 AM, Al Kossow via cctalk wrote:
The 4" drum in a IBM 650 is said to have rotated at 12,500 RPM.
On 5/10/18 9:29 AM, Paul Koning via cctalk wrote:
Just checked, and the LGP-30
and RPC-4000 drums are both listed as 3600 rpm
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. 
1:46 p.m.
On Thu, 10 May 2018, Al Kossow via cctalk wrote:
On 5/10/18 10:37 AM, Al Kossow via cctalk wrote:
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!):
http://bitsavers.org/pdf/ibm/sage/3-42-0_Drum_System_Sep58.pdf
Here's one of the earlier style R/W heads:
http://q7.neurotica.com/Oldtech/SAGE/DrumHead-1L.jpg
Mike Loewen mloewen at cpumagic.scol.pa.us
Old Technology http://q7.neurotica.com/Oldtech/
On 5/10/18 9:29 AM, Paul Koning via cctalk wrote:
Just checked, and the LGP-30 and RPC-4000 drums are both listed as 3600 rpm 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. 
11:18 p.m.
The good old days...
I recall the Q-7 drums would take about 15 minutes to come to a stop when
turned off, and would power up in seven seconds or less. Surge current was
around 115 amps?
Paul
On Thu, May 10, 2018 at 3:46 PM, Mike Loewen via cctalk <
cctalk at classiccmp.org> wrote:
On Thu, 10 May 2018, Al Kossow via cctalk wrote:
On 5/10/18 10:37 AM, Al Kossow via cctalk wrote:
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!):
http://bitsavers.org/pdf/ibm/sage/3-42-0_Drum_System_Sep58.pdf
Here's one of the earlier style R/W heads:
http://q7.neurotica.com/Oldtech/SAGE/DrumHead-1L.jpg
Mike Loewen mloewen at cpumagic.scol.pa.us
Old Technology http://q7.neurotica.com/Oldtech/
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
Just checked, and the LGP-30 and RPC-4000 drums are both listed as 3600
rpm
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.
11 May
11 May
4:49 a.m.
The manual says 125A per phase (3-phase, 208V) starting current.
I remember spin-down as 20 minutes, but that was a long time ago. :-)
On Fri, 11 May 2018, Paul Anderson wrote:
The good old days...
I recall the Q-7 drums would take about 15 minutes to come to a stop when
turned off, and would power up in seven seconds or less. Surge current was
around 115 amps?
Paul
On Thu, May 10, 2018 at 3:46 PM, Mike Loewen via cctalk <
cctalk at classiccmp.org> wrote:
Mike Loewen mloewen at cpumagic.scol.pa.us
Old Technology http://q7.neurotica.com/Oldtech/
On Thu, 10 May 2018, Al Kossow via cctalk wrote:
On 5/10/18 10:37 AM, Al Kossow via cctalk wrote:
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!):
http://bitsavers.org/pdf/ibm/sage/3-42-0_Drum_System_Sep58.pdf
Here's one of the earlier style R/W heads:
http://q7.neurotica.com/Oldtech/SAGE/DrumHead-1L.jpg
Mike Loewen mloewen at cpumagic.scol.pa.us
Old Technology http://q7.neurotica.com/Oldtech/
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
10 May
10 May
10:47 a.m.
The fixed head disc used on MU5 had a 20.5ms revolution time and an inner
track data rate of 2.2Mbytes/sec.
Regards
Rob
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Paul
Koning via cctalk
Sent: 10 May 2018 17:30
To: Grif <grif615 at mindspring.com>
Cc: General Discussion: On-Topic and Off-Topic Posts
<cctalk at classiccmp.org>
Subject: Re: how fast were drum memories?
> On May 10, 2018, at 10:37 AM, Grif <grif615 at mindspring.com> wrote:
>
>
> I wonder how the late generation paging disks (fixed head per track)
like
DG used in the 80's compared?
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).
Transfer rate is 0.5 megabytes per second, but still,
at that RPM, average
latency is 8.5 ms.
paul
2378
days inactive
2379
days old
10 comments
8 participants
participants (8)
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aek＠bitsavers.org -
billdegnan＠gmail.com -
grif615＠mindspring.com -
mloewen＠cpumagic.scol.pa.us -
paulkoning＠comcast.net -
phb.hfx＠gmail.com -
robert.jarratt＠ntlworld.com -
useddec＠gmail.com