[cctalk] Re: Bendix G-15 Restoration

[Dave Wade G4UGM via cctalk]

> -Original Message-
> From: Jon Elson via cctalk 
> Sent: 08 October 2022 03:10
> To: ben via cctalk 
> Cc: Jon Elson 
> Subject: [cctalk] Re: Bendix G-15 Restoration
> 
> On 10/7/22 18:14, ben via cctalk wrote:
> > On 2022-10-07 1:09 p.m., paul.kimpel--- via cctalk wrote:
> >> We'd all like to see the ALGO compiler, but be forewarned
> >> -- it's something like 14 passes on paper tape, with intermediate
> >> results punched on paper tape. I understand it's a bit more
> >> convenient to use if you have magnetic tape drives, but it's still
> >> going to be slow -- there's only so much you can do with 2K words of
> >> memory.
> >
> > Trying to hide the fact  the drum makes it slow.
> > Did any one ever replace the drum with core memory, on the early
> > serial computers?
> > Ben.
> >
> Tghe G-15 was a serial computer with an 90 KHz bit clock. The entire
> organization of teh computer revolved around the drum (pun intended).  There
> was an optimizer that organized instructions around the drum so that the next
> instruction came up on the read head just as the last instruction
> finished.  Without tearing the entire machine apart and redesigning the logic,
> core would not make it faster.
> 

I know the Ferranti Pegasus which is/was a serial machine everything was 
clocked to the drum. If the drum failed there was a special set of hardware to 
re-write the clock track.
Whilst replacing the clock would not have been hard, I don't think adding core 
would have helped there because everything was so integrated.
.. it used delay lines for registers which ran at the same speed so everything 
just worked...

> The PDP-8S did have core memory, and for a bit serial computer, it was fairly
> fast.
> 

For calculation, I believe the G-15 was fast. I can't believe any one would 
seriously run a high level compiler on such a machine.

> Jon

Dave

[cctalk] Re: Bendix G-15 Restoration

[paul.kimpel--- via cctalk]

Paul Pierce in Portland, Oregon has a copy on paper tape, but the tapes have 
been water-damaged and will require restoration. He told me that is on his list 
of projects, but it will be a while until he can get to it. There may be other 
copies, but I don't know of them at present.

[cctalk] Re: Bendix G-15 Restoration

[Paul Kimpel via cctalk]

*From:* Jon Elson via cctalk 
*Subject:* [cctalk] Re: Bendix G-15 Restoration
*Date:* Friday, October 7, 2022 at 7:10 PM
*To:* ben via cctalk 
*Cc:* Jon Elson 


On 10/7/22 18:14, ben via cctalk wrote:

On 2022-10-07 1:09 p.m., paul.kimpel--- via cctalk wrote:
We'd all like to see the ALGO compiler, but be forewarned -- it's 
something like 14 passes on paper tape, with intermediate results 
punched on paper tape. I understand it's a bit more convenient to 
use if you have magnetic tape drives, but it's still going to be 
slow -- there's only so much you can do with 2K words of memory.


Trying to hide the fact  the drum makes it slow.
Did any one ever replace the drum with core memory, on the early 
serial computers?

Ben.

Tghe G-15 was a serial computer with an 90 KHz bit clock.  The entire 
organization of teh computer revolved around the drum (pun intended).  
There was an optimizer that organized instructions around the drum so 
that the next instruction came up on the read head just as the last 
instruction finished.  Without tearing the entire machine apart and 
redesigning the logic, core would not make it faster.


The PDP-8S did have core memory, and for a bit serial computer, it was 
fairly fast.


Jon


With respect to timing, it depends what you mean by "bit clock." The 
drum rotated at 1800 rpm and there were 3596 bits recorded along its 
circumference (124 words of 29 bits), so that works out to 107,880 
bits/s. That is a bit period of 9.3 µs, which is what the G-15 Theory of 
Operation manual calls a "pulse period." A pulse period, however, was 
divided by the clock chassis into phases of 1 µs, 6.3 µs, and 2 µs, so 
the internal frequency of the logic was higher, if somewhat irregular.


That said, Jon is absolutely right about replacing the drum with some 
sort of random-access memory -- you would need to extensively redesign 
the logic of the machine to take advantage of the new memory. You would 
also have to modify a lot of the software. Timing dependencies aside, 
G-15 instructions didn't have addresses -- they had "timing numbers" 
that effectively told the hardware how long to wait before reading or 
writing a word on the drum.


Paul

[cctalk] Re: Bendix G-15 Restoration

[Van Snyder via cctalk]

On Fri, 2022-10-07 at 18:17 -0700, Chuck Guzis via cctalk wrote:
> 
> I recall that the IBM 650 had an upgrade option where core was used
> for
> some of the registers.  It was small--maybe 50 words.

Until it moved from Sindelfingen to the IBM Tech Center in Böblingen,
the collection at Haus zur Geschichte der IBM Datebverarbeitung (House
of the History of IBM Data Processing) included a 650 in working order.
It belonged to a museum or university in Vienna and was returned when
the collection moved. I hope it survived the return journey. Hans
Spengler  was one of the staff who maintained the
650. He would likely know whether a core accessory had been available.

[cctalk] Re: Bendix G-15 Restoration

[Cory Heisterkamp via cctalk]

> On Oct 7, 2022, at 6:14 PM, ben via cctalk  wrote:
> 
> Trying to hide the fact  the drum makes it slow.
> Did any one ever replace the drum with core memory, on the early serial 
> computers?
> Ben.
> 

While not in the interest of increasing throughput, “vintage” computers with 
drums that continued to soldier on well after their expiration date did require 
a more modern memory alternative. The LINK GP-4 that I posted about in 2016 at 
the Northwest Airlines Simulation Center was one such computer. Sadly sold for 
scrap, it had a “solid state drum emulator", loadable via 3.5” diskette. Pics 
here: https://goo.gl/photos/yb83SJSj67gS96n39 
-C