- cctalk - classiccmp.org

by Steve Lewis

Hey all! So, I've found myself studying up on RS-232 this year for a few reasons. I'm mulling over doing an RS232 themed talk at June VCF. Not a super exciting topic, but I do think that RS232 has an interesting history: In the SAGE relationship, and as a follow up to (essentially) prior telegraph communication. From what I've read, "50 baud" was a kind of an initial goal to beat, since that's what the top telegraph operators could achieve (in small burst, probably not all day). And those operators did have to also deal with things like start/stop "bits". Maybe it wasn't an intentional goal, but just that it establishes why "50 baud" is generally the lowest we ever see mentioned (or, if you go slower than that, might as well use the older tech). Then 75/110/130 baud to have digital-systems interoperate with classic mechanical teletypes. Going any faster and those systems jam up or overheat? These weren't yet called "serial ports", so I'm not sure what a late 50s system would even call their equipment that facilitate this data exchange (since I'm not sure what kind of crystal-clock they even had yet). Then, was it the SAGE program that demonstrated the idea of doing this kind of data exchange across copper phone lines? That is, the idea of computers collaborating not just in a room, but across long distances (miles)? And doing so by using an audio tone presentation? (they settled on around 3100MHz, which ended up translating to 300 baud? hence, that's basically why the first digital to digital system data exchange settled on that baud rate, which was reliable on both 50 and 60Hz power systems, and meaningfully faster than prior 110 baud - so a good milestone to turn it into a product, which was the Bell Model 103?). I couldn't find much details (like a manual) on the Bell 101 equipment (anyone seen one or have a manual?). But I did find the Bell 103 manual - the photo of its innards is grainy, so I don't understand how the Bell 103 did 300 baud without a UART (and one of the pinout lines I see did run power, so not sure if that's-yet RS232 or not; I know RS232 was evolving right at that same time circa 1962). I've about the 1970ish TR1402 initial DIP UART, with anything prior being an experiment (like a full board concept by DEC). I know from 1962, both RS232 and ASCII standards still took maybe another decade to really gain traction as standards (at least, from what I've read). Getting the world to comply with any standard always takes a lot of effort (for a practical reason of everyone still having invested in the older tooling that was still functional). But it's interesting how those two standards are still in use (not in their original form, but least the 1967 revisions) - extending from Baudot.and late 1800s-tech on telegraphs. Does anyone know of any grocery stories using RS232 in the 1960s? I think barcode scanning was just introduced in that era. I can just imagine a smart grocery store owner, in the backroom programming their minicomputer for payroll and inventory management. In FORTRAN and without a CRT? Actually, in the 60s, I think included software would be negotiated with the provider of the computer (well, I'm not sure how that differed between minis and mainframes). I know early microcomputers used RS232 for keyboards (1974-1976 era). The IBM PC keyboard is essentially another form of serial. Well, sorry for the rambling - have other RS232 related questions, but first wanted to focus on the historical aspects (and see if I'm somewhat on the right track at least). -Steve

1 year, 2 months

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Ad-blocking (was Re: Open source a panacea?)

by John

On Fri, 14 Feb 2025 12:00:07 -0600 cctalk-request(a)classiccmp.org wrote: > I can't believe people do use it any more without filtering. I've > used an ad-blocking web browser for some years but I occasionally see > the real thing when setting up a new machine. Absurd. It really is astonishing how bad it's gotten - fully the equal of the early '00s when sites might just spawn a dozen pop-ups and only one of the major browsers let you block them, only now there's a pile of JS mining crypto in the background, to boot :/ Been running with NoScript and an ad-blocker as my standard configuration for many, many years now, but it's always sobering to get a look at what other people see...

1 year, 2 months

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NCR EM-D2 Card reader manual

by Mattis Lind

I am about to get a NCR EM-D2 card reader, but I can not find much documentation on it. Is there anyone here that has documentation on it? Preferably a maintenance manual. A couple of years ago (perhaps in February 2021 if one studies how they indexed the file in their storage) there was a sale of a maintenance manual on Ebay according to the below Worthpoint link. https://www.worthpoint.com/worthopedia/1965-ncr-em-d2-punched-card-reader-3… Did anyone here buy this manual? I am very interested in a scan of this manual or possibly to purchase the manual. /Mattis

1 year, 2 months

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Mid-Atlantic Retro Computing Hobbyists Hack-a-Thon

by Jeffrey Brace

DATE: March 8 & 9, 2025 LOCATION: InfoAge Science and History Museums, Wall, NJ Fee: None *More info here*: https://vcfed.org/2025/02/13/march-hack-a-thon/

1 year, 2 months

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Looking for information on Megan Gentry, former RT-11 developer

by Hans-Ulrich Hölscher

Does anyone know anything about the whereabouts of Megan Gentry, former RT-11 developer? She left her last trace in 2020, when she ported ZEMU to RT-11.

1 year, 2 months

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Vintage Computer Festival Montreal Survey

by Jeffrey Brace

We invite you to take part in a brief, anonymous survey about VCF Montreal. Click here https://bit.ly/vcfm2026pre-en Nous vous invitons à participer à un bref sondage anonyme sur VCF Montréal. Cliquez ici https://bit.ly/vcfm2026pre-fr Jeff Brace Vintage Computer Federation Vice President

1 year, 2 months

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Use (abuse?) of a 7924 in a +24 PS...

by William Sudbrink

I'm repairing/restoring a later model MITS 8 inch floppy drive. I can not seem to find schematics for it. It is the same as Bill Degnan has here: https://vintagecomputer.net/MITS/88-DCDD/ You can see in his photos (and mine match) that the _plus_ 24 volt DC supply on the board uses a 7924 (note the 9. negative) voltage regulator, with a small heat sink, directly on the circuit board. Along with a couple of 7805s, there is a .Motorola 2n6045 screwed to the large black heat sink. All three of the devices drop into sockets on the circuit board to allow the heat sink to be easily installed/removed. On my unit, the socket for the 2n6045 was burnt to a crisp. I have replace the socket, the 2n6045, the 7924 and the electrolytic caps. When I test the +24 volt rail with a dummy load, it measures +41 volts. I don't understand this circuit. I know MITS was notorious for its power supplies. Does anyone have the schematics for this version of the 8 inch floppy? Any suggestions? Thanks, Bill S. -- This email has been checked for viruses by Avast antivirus software. www.avast.com

1 year, 2 months