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replacement for 80286

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    #16
    more to the point: why? clock for clock the 386sx is not faster than a 286, so unless you need to run 32bit code it's not gaining you anything

    Comment


      #17
      Originally posted by AndyM1981 View Post
      Is that even a thing? Even though they both use a 16-bit bus I would assume that there are enough differences that you just can't pop in a 386SX and have it work. There are the likely differences in pin out, communications with the bus and BIOS support to name a few off the top of my head.
      Not all that much difference. Some of the very early 386SX computers used 286 motherboards with a tiny daughtercard to hold the 386SX. Everex was one that did that in the rush to get a 386SX out the door.

      Note that some of the upgrade boards included an oscillator allowing for a nice clock speed boost.
      Last edited by krebizfan; March 26, 2020, 07:12 AM.

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        #18
        Originally posted by maxtherabbit View Post
        more to the point: why? clock for clock the 386sx is not faster than a 286, so unless you need to run 32bit code it's not gaining you anything
        The one reason I can think of for it is if you have a 286 with a lot of extended memory you’d like to be able to use as EMS, or to run multitaskers like Desqview.

        Note of course that *most* 386sx upgrade boards sold commercially did have more than just the CPU on them because they often included some cache memory and a circuit to allow the CPU to run faster than the bus, but a very few “feature only” adapters that ran the CPU at the native speed did exist. It would be sort of amusing to have one of those in an original 6mhz AT.
        My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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          #19
          Very interesting! I had no idea that the 386SX was that close to the 286 electrically. Thanks for the interesting lesson all!

          Comment


            #20
            It's kind of strange in retrospect that when clone CPUs from AMD and Cyrix became a thing that nobody released a 386sx variant in PGA and PLCC packages to directly plug into 286s. (From a strategic standpoint it makes sense that Intel didn't, because they really wanted to push new computer sales.) Cyrix in particular made internally clock-doubled 386sx clone CPUs that they could have packaged as plug-and-play boardless upgrades.
            My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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              #21
              Don't forget that the 386SX was a "budget" notion. Why waste money on that, when you can sell the "full bodied" version? I don't see why a 386SX couldn't be soldered to a PGA carrier board, if that was really needed. I may even have seen such a beast.
              Reach me: vcfblackhole _at_ protonmail dot com.

              Comment


                #22
                Here's a page that has a picture of a prototype/sample 386sx "upgrade option" chip in a 286 compatible PGA package. Apparently Intel at least *considered* selling such an upgrade chip that didn't require a carrier.
                My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

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                  #23
                  Originally posted by Eudimorphodon View Post
                  The main problem is Intel never released the SX in a physically compatible form factor; it *only* came in a surface mount flat pack, so you need an adapter board to put it in a 286 socket.
                  In the early days that was the main reason I let this idea go: you really need a decent PCB. The CPU in those days was too expensive for just a hobby project. And PCBs were not cheap then as well. Nowadays it could be a nice hobby project but I have too much other project running. And what should I do with the machine once finished? But I will place it on my list "To do in a very far future...".
                  But in case somebody has some plans of his own, please let me know!
                  With kind regards / met vriendelijke groet, Ruud Baltissen

                  www.baltissen.org

                  Comment


                    #24
                    This would make for a very interesting project indeed. If someone ever did it I hope they would share the results!

                    Comment


                      #25
                      Originally posted by krebizfan View Post
                      There were kits with the higher clock oscillator and updated BIOS to go along with the new CPU. Note that the 10 MHz AT variant from IBM was a bit unreliable so pushing that far might be unwise. It wasn't 5170 but I think was the industrial system.
                      Do you have any sources for the existence of the 10MHz AT variant? I've never heard of this before, except for the existence of some prototypes. I have seen IBM made "Turbo" AT motherboards listed on TH99, but I assumed those must be errors.
                      "Will the Highways on the internets become more few?"

                      V'Ger XT

                      Comment


                        #26
                        Originally posted by Anonymous Coward View Post
                        Do you have any sources for the existence of the 10MHz AT variant? I've never heard of this before, except for the existence of some prototypes. I have seen IBM made "Turbo" AT motherboards listed on TH99, but I assumed those must be errors.
                        Code:
                        7552-040 h IBM PC/AT System Unit (10MHz, 512KB)
                        Hardened, for use without keyboard or display via Remote Terminal Interface
                        7552-540 h IBM PC/AT System Unit (10MHz, 512KB)
                        Hardened, 20MB fixed disk for use without keyboard or display via Remote
                        Terminal Interface
                        Taken from page 46 of the Sep 88 Product Reference. I have never seen one and what I heard about it indicates some software didn't work on it which is why it went with a terminal interface.

                        Comment


                          #27
                          Originally posted by krebizfan View Post
                          Code:
                          7552-040 h IBM PC/AT System Unit (10MHz, 512KB)
                          Hardened, for use without keyboard or display via Remote Terminal Interface
                          7552-540 h IBM PC/AT System Unit (10MHz, 512KB)
                          Hardened, 20MB fixed disk for use without keyboard or display via Remote
                          Terminal Interface
                          Taken from page 46 of the Sep 88 Product Reference. I have never seen one and what I heard about it indicates some software didn't work on it which is why it went with a terminal interface.
                          I read a little about IBM 7552 in a copy of a document I found on Google Books. It sounds like it is an MCA/ISA hybrid, so it may not have an AT motherboard afterall.

                          https://books.google.co.jp/books?id=...010mhz&f=false

                          A VCfed member actually bought one and took photos of it too:

                          http://www.vcfed.org/forum/archive/i...p/t-22672.html
                          Last edited by Anonymous Coward; March 28, 2020, 04:41 PM.
                          "Will the Highways on the internets become more few?"

                          V'Ger XT

                          Comment


                            #28
                            Network World has the earliest description of the 7552 online from 1986 https://books.google.com/books?id=nx...207552&f=false

                            I doubt it had a prerelease version of MCA but as a passive backplane system, adding support for MCA should be relatively easy. I can't find the 7552 related IBM announcements but I think the Microchannel industrial line up wasn't introduced until 1989.

                            Comment


                              #29
                              Originally posted by krebizfan View Post
                              Network World has the earliest description of the 7552 online from 1986 https://books.google.com/books?id=nx...207552&f=false

                              I doubt it had a prerelease version of MCA but as a passive backplane system, adding support for MCA should be relatively easy. I can't find the 7552 related IBM announcements but I think the Microchannel industrial line up wasn't introduced until 1989.
                              What's clear from the first document I linked to is that this system is not using a 5170 motherboard, and it's not even completely AT compatible as claimed because some signals are missing from the ISA slots.
                              "Will the Highways on the internets become more few?"

                              V'Ger XT

                              Comment


                                #30
                                It certainly doesn't sound any more like a "10 mhz variant of the AT" then the PS/2 Model 50 is. Or maybe more charitably, the PS/2 Model 30/286?

                                Funny how IBM was apparently allergic to using the 12mhz 80286, I'm pretty sure those were in wide circulation by 1987. Certainly by 1988 when the 30/286 came out.
                                My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs Also: Blogspot

                                Comment

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