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full 640 KB memory on IBM 5150 unnecessary?

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    full 640 KB memory on IBM 5150 unnecessary?

    I recall someone saying that 640KB would be "overkill" for 4.77Mhz machines that the games requiring it won't run propely in such computer anyway. Is that true?

    Originally my IBM 5150 came with 256kb card making it 512Kb total (256kb dram onboard), but I have been using this ram card instead and with it I can get full 640kb but I still don't know what is the actual size of this memory expansion? 1Mb?

    s-l1600 (2).jpg


    My IBM PC is only for CGA games that runs too fast with my 286 (8Mhz).
    Last edited by musicforlife; February 15, 2018, 12:34 PM.

    #2
    I don't think so. There's quite a lot of software that needs 640k, or at least works better with 640k.
    http://scalibq.wordpress.com/just-ke...o-programming/

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      #3
      Two banks of 256Kbit memory. This gives 512KB total on this card.

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        #4
        That's a 512K card (18 x 256x1 DRAM).

        The first edition 5150s used 16Kx1 DRAM and so maxed out at 64K on the motherboard. There were add-on mods to allow them to take the 64Kx1 DRAMs for a total of 256K.

        Almost immediately after purchasing my 5150, I opted for a memory expansion card. You couldn't do a lot with only 64K, although that was plenty on an 8-bit CP/M system for most things.
        Reach me: vcfblackhole _at_ protonmail dot com.

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          #5
          Depends on what you do with the machine. More memory is almost always better, especially if you're running a later DOS (e.g. 5 through 6.22).
          Check out The Glitch Works | My Retro Projects | Vintage Computer Services | Glitch Works Tindie Store -- Vintage Computer Kits and More

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            #6
            Even software that can't see the full 640k could benefit from running off a RAM disk. Makes loading overlays a lot faster.

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              #7
              "640K ought to be enough for anybody."

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                #8
                I've just upgraded my 5160 XT motherboard (4.77MHz too) to 640K. The most challenging was to find a con-temporary 41256 chips...

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                  #9
                  Look around on the forum for the way to upgrade a 5160 to use 1MB (all 41256 chips) to put RAM into some high-memory locations by replacing a single PROM.
                  Reach me: vcfblackhole _at_ protonmail dot com.

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                    #10
                    The only advantage in not having 640K is waiting a little less for it to be checked during POST.

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                      #11
                      Mine has 640K using a SixPakPlus but I also use a lo-tech 2M EMS ram. It helps in apps that need them like Windows 3.0 or Borland C compiler.

                      PKZip also uses EMS.

                      And I modded mine to 6.66Mhz using a V20 adding turbo switch and reset button.

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                        #12
                        Originally posted by glitch View Post
                        Depends on what you do with the machine. More memory is almost always better, especially if you're running a later DOS (e.g. 5 through 6.22).
                        I'm playing CGA games that are running too fast in my 286 (8Mhz) and using DOS 3.20 in hard drive (going for floppy-only with 2.1 when getting my original IBM floppy drives fixed).

                        I use another 286 for later era CGA games that required more power (amazing that someone still made games for CGA-only in 1991).


                        Originally posted by Retro Canada View Post
                        And I modded mine to 6.66Mhz using a V20 adding turbo switch and reset button.
                        Can you retain the original 4.77Mhz speed with that mod? I specifically got IBM PC for the earliest CGA games.

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                          #13
                          Originally posted by vwestlife View Post
                          The only advantage in not having 640K is waiting a little less for it to be checked during POST.
                          Right--and the reason that people have these things is because they're so amazingly fast!

                          I seem to recall that the memory test only applies when "cold" booting--doing a three-key-salute boot bypasses it.
                          Reach me: vcfblackhole _at_ protonmail dot com.

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                            #14
                            A full 640k is pretty much a must-have, even for a 5150. Many commercial DOS programs continued to target 8088 real-mode well in to the 90s, but usually made the assumption that such machines were maxed out with 640k.

                            Operating with 256k, you will constantly run in to "insufficient memory" errors.

                            There were only a very tiny handful of early programs that would get unhappy with "too much" RAM. And usually those can easily be worked around by loading some resident program first, or using a software tool to adjust the reported RAM size.

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                              #15
                              Originally posted by SomeGuy View Post
                              A full 640k is pretty much a must-have, even for a 5150. Many commercial DOS programs continued to target 8088 real-mode well in to the 90s, but usually made the assumption that such machines were maxed out with 640k.

                              Operating with 256k, you will constantly run in to "insufficient memory" errors.

                              There were only a very tiny handful of early programs that would get unhappy with "too much" RAM. And usually those can easily be worked around by loading some resident program first, or using a software tool to adjust the reported RAM size.
                              Originally my IBM PC came with another memory expansion card making 512Kb total.

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