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IBM EGA Card Memory Expansion Boards

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    #46
    I posted pictures of the normal one. Here's the early? One.
    You do not have permission to view this gallery.
    This gallery has 4 photos.
    I have a Major in Post-Apocalyptic Economics.
    Wanted: Any PC-Compatible Reciprocation Dingle Arm

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      #47
      I got one of those last year from an ebay seller, he was selling like 70 or so of them.

      I do have a question: is it possible to redesign the board to use two 44256 DRAM chips? I know 64K would be wasted, but still, fewer ICs would make the board much smaller and less hot.

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        #48
        Originally posted by dhau View Post
        I got one of those last year from an ebay seller, he was selling like 70 or so of them.

        I do have a question: is it possible to redesign the board to use two 44256 DRAM chips? I know 64K would be wasted, but still, fewer ICs would make the board much smaller and less hot.
        Does yours report 256k when installed?
        I have a Major in Post-Apocalyptic Economics.
        Wanted: Any PC-Compatible Reciprocation Dingle Arm

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          #49
          Originally posted by offensive_Jerk View Post
          I posted pictures of the normal one. Here's the early? One.
          This is it exactly. Same hand-written part number on the back: 700137-000 rev. 0 and a serial number. (For the sake of Google) There's a sticker on the front that reads "International Technology Corp." -- which is not exactly a unique and identifiable name. Could be a reseller, IBM partner, or is this an early clone part? It certainly looks like a genuine IBM part.

          About the detected memory, I haven't actually tried this card yet. I just had my 5170 (which has the EGA card installed in it) out on the bench last weekend, but I didn't get around to installing the expansion yet. I have a few things I want to do on that machine, and this is one of them, but I don't power-up anything with 30 year old tantalums until I've replaced them all.

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            #50
            Originally posted by ElHack View Post

            This is it exactly. Same hand-written part number on the back: 700137-000 rev. 0 and a serial number. (For the sake of Google) There's a sticker on the front that reads "International Technology Corp." -- which is not exactly a unique and identifiable name. Could be a reseller, IBM partner, or is this an early clone part? It certainly looks like a genuine IBM part.

            About the detected memory, I haven't actually tried this card yet. I just had my 5170 (which has the EGA card installed in it) out on the bench last weekend, but I didn't get around to installing the expansion yet. I have a few things I want to do on that machine, and this is one of them, but I don't power-up anything with 30 year old tantalums until I've replaced them all.
            You guys are killing me
            I NEED to know if your cards behave like mine.
            A funny think I noticed when trouble shooting the 030201 issue is when I looked at the ram module in that bank, one of the legs was not in the socket. Not sure if whomever did that did it on accident....or......
            I have a Major in Post-Apocalyptic Economics.
            Wanted: Any PC-Compatible Reciprocation Dingle Arm

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              #51
              Originally posted by ElHack View Post

              This is it exactly. Same hand-written part number on the back: 700137-000 rev. 0 and a serial number. (For the sake of Google) There's a sticker on the front that reads "International Technology Corp." -- which is not exactly a unique and identifiable name. Could be a reseller, IBM partner, or is this an early clone part? It certainly looks like a genuine IBM part.
              Here's mine
              You do not have permission to view this gallery.
              This gallery has 1 photos.
              I have a Major in Post-Apocalyptic Economics.
              Wanted: Any PC-Compatible Reciprocation Dingle Arm

              Comment


                #52
                Is there suddenly a demand for IBM EGA + Expansion? There really isn't any advantage to other clone cards and monitors are in short supply. I wouldn't resort to dodgy computer reset versions. It makes me wonder if they were looking to repurpose unused stock for a customer request since it's being indicated there are a handful of these found there like this? They certainly don't resemble what's pictured in IBM documentation with those modifications on there.

                The expansion board has been cloned and works just fine. I have almost enough for assembling a second one here from my order, collecting dust, if someone was looking for one of these.

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                  #53
                  Monotech made a very nice replica of the IBM EGA expansion card, they did it the way I prefer, an exact pcb replica, so there are no surprises or unexpected protocols and it is very economical too as it comes as a kit. I'm glad they did it, I was about to replicate it myself at one point when I could not get one:

                  https://monotech.fwscart.com/IBM_EGA..._20493600.aspx

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                    #54
                    Originally posted by the3dfxdude View Post
                    Is there suddenly a demand for IBM EGA + Expansion? There really isn't any advantage to other clone cards and monitors are in short supply. I wouldn't resort to dodgy computer reset versions. It makes me wonder if they were looking to repurpose unused stock for a customer request since it's being indicated there are a handful of these found there like this? They certainly don't resemble what's pictured in IBM documentation with those modifications on there.
                    Probably not. This is more of an attempt to discover some history. The card I have looks like an IBM part, but with some clues that it might not be, and I'm curious about its origin story. I came across this thread while Googling for scraps of info, and figured while I was here, I might as well drop some observations and physical specs for anyone either looking for the same, or hoping to build their own. There were some questions about hole diameters and fitment that I thought I could add to, although if my card is not a genuine IBM part, it might be best taken with a grain of salt. At the very least, if someone's finding this 10 years down the road and all the hobby replicas have vanished, maybe it'll help someone cook up their own.


                    Originally posted by offensive_Jerk View Post
                    You guys are killing me
                    I NEED to know if your cards behave like mine.
                    Haha ... sorry man. I got some memory chips in the mail to feed a couple of my other machines, so I've got the Tandy 1000 on the bench today. But I'll try and make a point of getting this card installed this week, and I'll report back whether Check It and the AT Diags disk gives the thumbs-up. I don't know if it matters for the sake of testing, but I only have a CGA monitor available at the moment. I do have a 5154 as well, but I have not taken it apart yet since receiving it in the mail. After having received a Trinitron with a crack in the PCB under the flyback transformer, I'm careful to inspect them before applying power. And may as well go ahead and re-cap while I'm in there, too. For better but sometimes worse, I'm exhaustively thorough, which means I often have a dizzying backlog of work to do before I get to play with new toys.

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                      #55
                      Originally posted by ElHack View Post
                      Probably not. This is more of an attempt to discover some history. The card I have looks like an IBM part, but with some clues that it might not be, and I'm curious about its origin story. I came across this thread while Googling for scraps of info, and figured while I was here, I might as well drop some observations and physical specs for anyone either looking for the same, or hoping to build their own. There were some questions about hole diameters and fitment that I thought I could add to, although if my card is not a genuine IBM part, it might be best taken with a grain of salt. At the very least, if someone's finding this 10 years down the road and all the hobby replicas have vanished, maybe it'll help someone cook up their own.
                      Sure history is good to see. I'm sure they are originally IBM based on the markings, but they look modified. I thought the original daughter card came with a plastic shield for the solder side of the card, to protect it from making contact with the card in the next slot during install. Components soldered on the back side would mean it could not have that. ab0tj's clone is a good working design, and gerbers are available, and the holes can be adjusted if needed. If you had to order the ram anyway, and assembling not an issue, all you need is a pcb, which I have extra, and a few other inexpensive parts. You'd probably only spend about 10$ for the parts. Might be a better way to go.

                      Comment


                        #56
                        Originally posted by dhau View Post
                        I do have a question: is it possible to redesign the board to use two 44256 DRAM chips? I know 64K would be wasted, but still, fewer ICs would make the board much smaller and less hot.
                        Hard no. EGA uses a "Planar" memory organization in which the 16 color graphics modes each draw 1 bit of color information from four parallel banks of memory. (These bits are then combined into a single pixel through the palette register.) This memory is fetched a byte at a time from each bank and fed out pixel-by-pixel through four separate shift registers, so in essence from the video hardware's standpoint the RAM interface is 32 bits wide, not eight.

                        If you look at an old 256K VGA card with 8 RAM chips on it you'll find it's four sets of 4464s (64k by 32 bits), not one set of 41256s (256k by 8 bits). Same deal. Clone EGA cards also often (I'm actually going to go so far as say "usually") use this arrangement because, yeah, it saves a ton of space, with the only downside being that you need to sell the card with 256k already on it. (In theory you could probably make an EGA card that had sockets that could take either 4416s or 4464s, as long as you're happy with the only two memory options being 64k and 256k, nothing in-between; this is frankly what IBM probably should have done.)

                        A memory card with eight 4464s (still wasting a quarter of it because of how the memory is arranged) instead of the 24 4416s *might* be an option? You'd have to add some tricky logic to turn the separate CAS/RAS signals for the three sets of 16K in each of the four banks into memory addresses within the single 64K set you're doing instead. And there may be some additional complication relating to refresh I'm not thinking of, so I'm not going to go any further than saying it's a theoretical possibility.

                        (You know, if you really wanted to be fancy you might be able to use a 72 pin SIMM for an EGA expansion card, but it'd have to be a really tiny one, and you'd still of course need the aforementioned logic to fudge CAS lines into address bits.)
                        Last edited by Eudimorphodon; October 22, 2021, 04:31 PM.
                        My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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                          #57
                          I believe 90degree SIMM sockets are a thing, I know I've seen them in 45degree

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                            #58
                            When I said "tiny" in reference to a SIMM I was thinking in terms of capacity. The thing that makes me worry that adapting larger chips would be even harder than just turning CAS signals into address bits is you might also need to somehow regenerate/mangle the RAS signals to get proper refresh. And that problem will get harder the more rows you add? Someone more skilled in DRAM black magic would be better to answer that question.
                            My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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                              #59
                              Originally posted by Eudimorphodon View Post
                              A memory card with eight 4464s (still wasting a quarter of it because of how the memory is arranged) instead of the 24 4416s *might* be an option? You'd have to add some tricky logic to turn the separate CAS/RAS signals for the three sets of 16K in each of the four banks into memory addresses within the single 64K set you're doing instead. And there may be some additional complication relating to refresh I'm not thinking of, so I'm not going to go any further than saying it's a theoretical possibility.
                              So it has to be two SRAM chips 32-bit x 256kwords? Something like this one: https://www.digchip.com/datasheets/p...255HLJP-12.php

                              Comment


                                #60
                                Originally posted by dhau View Post
                                So it has to be two SRAM chips 32-bit x 256kwords? Something like this one: https://www.digchip.com/datasheets/p...255HLJP-12.php
                                For this in addition to deriving additional address bits from decoding the CAS lines you're also going to have to demultiplex the address lines entirely. Which might not be too terrible. There are some things about the planar memory address generation I don't know without puzzling over the EGA manual(*), though, so I can't say how complicated it'll be. Does anyone know off the top of their head if the same memory address applies to all four planes *always*, or if there are cases where one or more planes have different effective addresses? I assume its the former because later VGA cards often used 16 bit wide DRAMs (with byte select lines to control which 8 bit half is read/written if not both), but IBM's EGA supporting 64k/128k/192k configs might make it a special case?

                                (* And of course IBM's EGA used some gate arrays, not discrete circuitry, for most of the really juicy parts, including DRAM address generation, so some of it still might not be entirely clear.)
                                My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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