Image Map Image Map
Results 1 to 4 of 4

Thread: IBM 5150 is alive! memory question.

  1. #1

    Default IBM 5150 is alive! memory question.

    I've had a 5150 for almost a year but never really tested it. it powered on and i heard beeps, but i didn't have a proper monitor for it.

    I recently picked up a cheap 5150 parts monitor from a salvage place and it works great. The 5150 was booting to a parity error 0, so i found the fix online, replaced the parity ram chip with a 4146 from some C64 projects, and it boots up fine.

    both the monitor and CPU are in excellent condition. I'm using a Tandy keyboard for now.

    I do not have a DOS disk yet. but i do have the guide to operations set which includes a diagnostic disk. everything seems to check out fine (memory, keyboard except for keys that Tandy does not seem to have, floppy drives, monitor, etc). I noticed that one of the disks in the 'guide' package, when attempting to boot to it, says it requires 64k to run. my system has 48k.

    question: can anyone point me to a tutorial on where/how/what to upgrade them ram? does 48k seem like an odd configuration for a 5150? and would it potentially use the 4146 memory chips which i have sleeves of?

    thanks for any help.

  2. #2
    Join Date
    May 2006
    Melbourne, Australia


    Lots of IBM 5150 information at

    Using that information, which type of 5150 motherboard do you have, '16KB-64KB' or '64KB-256KB ?

    With the IBM 5150, increasing conventional memory is done by first, populating all four motherboard RAM banks (with the type of RAM chip appropriate for the type of 5150 motherboard), then second, adding expansion cards that contain conventional memory.

    There is no mod to increase the size of the RAM chips used on the 5150 motherboard.

    With the IBM 5150, we have seen a lot of cases where the RAM switches on the motherboard (in both SW1 and SW2) have been set incorrectly. Not helped by the fact that the settings changed slightly with the introduction of the third revision BIOS. All switch settings can be found at

    Quote Originally Posted by Dokken View Post
    does 48k seem like an odd configuration for a 5150?
    A '16KB-64KB' motherboard with only three of the four RAM banks populated ?

    Incorrect motherboard switch settings ?

  3. #3


    thanks. i got bank 3 populated with RAM, set the jumpers, and it now shows 64k.

  4. #4
    Join Date
    May 2006
    Melbourne, Australia


    Understandably, there is not much you can do in a 5150 that has 64 KB of RAM.

    But now that you have fully populated the 5150's motherboard RAM, you are in a position to start adding RAM expansion cards (example memory map [here]).

    For where there are very few available expansion slots, there are RAM cards, such as the MEMO576, that can provide 576 KB of RAM, addressed from 64K to 640K.

    As you may have read at, the first two BIOS revisions of the 5150 have a limitation of 544 KB (conventional memory).


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts