[cctalk] Re: Odd IBM mass storage systems
The main storage area of the ElectroData/Burroughs Datatron 205 was 20 tracks of 200 words each for a total of 4000 words. The drum rotated at 3570 RPM, so the average access time was about 8.4ms. The four quick-access tracks (or "loops" as they were called) were 20 words each and worked as a delay line, much like the Bendix G-15's drum. These tracks had separate read and write heads. When writing was not taking place, the digits from the read head were simply copied to the write head 36 degrees behind on the surface of the drum. So as the last digit of the track was written, the first digit of the track was coming under the read head, yielding an average access time of 0.84ms. When writing, digits from the processor were shunted to the write head in lieu of those coming from the read head. When power was removed from the system, the 4000-word main memory was preserved, but the data in the high-speed bands was lost. The 205 had instructions to transfer 20-word blocks between the main memory and the high-speed tracks. There were even a couple of instructions to move a block to one of the high-speed tracks and branch to a word in that high-speed track. The high-speed tracks were addressed modulo 20 (i.e., word 4005 was the same as 4025, 4045, 4065, ... 4985). You had to get good at dealing with addresses that were congruent modulo 20. The high-speed tracks were so much faster than main storage that most programmers went to a lot of effort to "block" 20-word segments of the program to the high-speed tracks and execute at least the most active code from the faster storage.
[cctalk] Re: Odd IBM mass storage systems
The tape for the Burroughs 220 drives was not metallic. It was 3/4-inch wide, and I think a Mylar sandwich. It could be spliced much the same way you would have spliced quarter-inch reel-to-reel audio tape back in the day. If the tape controller detected a parity error, it would backspace the block and retry twice. If the error persisted on the second retry, the tape would stop with the head ready to read the bad block (hanging the processor in the middle of its I/O instruction), and the operator would have to take manual action. If the drive punched a hole in the tape, then the drive needed service -- probably a bad capstan pinch-roller solenoid.
[cctalk] Re: Paper tape in casettes...
erik＠baigar.de wrote: > > > think the Bendix G-15 had cassettes for the 5-level > > tape > > they used. > Aha, interesting! Did a short search, but have not been able to > find a picture of a casette. Just a pile of paper tape instead ;-) > > https://images.app.goo.gl/HYqkpYHJUxZeGfiA8 Bitsavers has a collection of G-15 manuals. For a picture of an open cassette, see PDF page 27 in http://bitsavers.org/pdf/bendix/g-15/60061400_G15D_Parts_Manual.pdf. Also see PDF page 18 in http://bitsavers.org/pdf/bendix/g-15/G15_Operating_Man_Jul59.pdf. David Lovett has been restoring a G-15 for the System Source Computer Museum in Maryland (US). He regularly publishes videos of his progress, such as this one: https://www.youtube.com/watch?v=WNfR4DmoZQU=ygUWYmVuZGl4IGctMTUgcGFwZXIgdGFwZQ%3D%3D To see more, try searching youtube.com for "bendix g-15 paper tape".
[cctalk] Re: mainframe vs mini
The term "mainframe" comes from telephone switching technology -- the electromechanical kind from before the time of electronic telephone switches. Its association with computers is from the earliest days of the commercial computer business and precedes the minicomputer era by quite a bit. As I understand it, in an electromechanical telephone switch, the "main frame" (note the space) was the rack where the central control and switching components for the switch were located. In a computer system, it usually applies to the cabinet where the CPU and memory reside, perhaps including the I/O controllers, as opposed to the peripheral components. The term "mainframe" is still used today for enterprise-class systems (to the horror of their marketing and advertising minions), even though the mainframe components may be wholly contained a 1U module for a 19-inch rack.
[cctalk] Re: on the origin of home computers
Yes, the G-15 was definitely a digital computer, but I'm not aware that it had any "add-on analog element," at least not any that was a standard Bendix product. There was a differential analyzer, the DA-1, that attached to the G-15 and used some of its drum memory lines for storage, but it was a digital differential analyzer, not an analog one. There was a connector on the back of the G-15 cabinet to which a user could attach data collection equipment, but this, too, was digital -- the external signals were made available in a one-word "Input Register" the G-15 could enable, disable, and read, but any A-to-D had to be done by the external interface to the system. As to the G-15 being a personal computer, I think it was pretty much in the same league as the LGP-30 in that respect. They had similar electrical and floor-space requirements, and their costs were not all the different, either. It was definitely a single-user system, and my impression is that the G-15 was typically operated by the people programming it. Its design was not conducive to closed-shop operations. There was at least one person who used a G-15 as their personal computer -- Harry Huskey, the designer. Apparently the deal he made with Bendix to do the design included him receiving a G-15 for his personal use.
[cctalk] Re: Mechanical Selectric keyboards on video terminals (was Re: Typing class in high school)
Paul Berger wrote: > On 2023-01-29 12:25 a.m., Chuck Guzis via cctalk wrote: > > On 1/28/23 20:20, Paul Berger via cctalk wrote: > > > > [snip] > > believe it is the same > > as the 029. The printer in the 1052 is a keyboardless Selectric with no > > tab rack and they spaced via a cam on the OP shaft instead of taking a > > cycle. The ones I saw on a couple 360s (22 and 25) the space cam was so > > worn it wobbled when it took a cycle, but the customer would never let > > us do anything with it as long as it worked because they could not do > > anything with out the console. Was the 1052 more or less durable than the > > model B > > adapted for the 1620? > >With its movable carriage, it always seemed to be in danger of > > self-destructing--the thing would shake a bit then a carriage return was > > executed. > > > > --Chuck > > My experience is that they where pretty durable, I never saw a lot of > 1052s by the time I started in 1979 there was not a lot of 360s in our > branch. [snip] > > I don't know how they would compare to a model B that was used as an I/O > I never saw any systems that used one. I would imagine that moving the > heavy carriage back on something that is printing steady would be a > trouble spot. I would image that kind of use would also be hard on the > power roll that drives the type hammers into the paper. I don't image > they would be very fast, a Selectric could print at 15.5 characters per > second and at that speed the cycle clutch never latched it was just one > continuous cycle. Selectric I/Os that ran at full 15.5 chars/sec > suffered way more problems than ones that printed at a lower speed. The IBM Model B electric typewriter was used as a printer and keyboard entry device on at least the Bendix G-15 (mid 1950s) and the IBM 1620 Model 1 (1959). On the G-15 it ran at about 8cps (timing was determined by the drum rotation). On the 1620-1 it ran at 10cps. And yeah, they probably took quite a beating, since many sites did not have a line printer. The 1620 Model 2 (1962) used a Model 731 Selectric and drove it at 15.5cps. Paul K
[cctalk] Re: Bendix G-15 Restoration
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
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.
[cctalk] Re: Bendix G-15 Restoration
I would also be interested in receiving a copy.
[cctalk] Re: Bendix G-15 Restoration
I recently completed an emulator for the G-15. It supports the basic machine configuration -- just paper tape and typewriter I/O -- but I'm interested in implementing other peripheral devices as software that uses them becomes available. The emulator attempts to run at the speed of a real G-15, which is pretty slow. It successfully passes the one diagnostic test I have. The emulator is web-based and should run in reasonably recent versions of any of the popular web browsers. I've tested it with Firefox, Google Chrome, Apple Safari, and Microsoft Edge. You can run the emulator directly from my hosting site at https://www.phkimpel.us/Bendix-G15/ or you can download the files from GitHub and run it from some other web server. Once the emulator loads into the browser, there's no further interaction with the server. >From the link above there are additional links to the GitHub repo, the wiki, >and additional resources. Issues concerning the emulator can be posted on the >GitHub repo. I don't currently have much software for the emulator, but am working with Rob Kolstad to curate a large stash that recently became available. What software I do have is available on a separate GitHub repo at https://github.com/retro-software/G15-software/. Additional contributions are welcome.
