Image Map Image Map
Results 1 to 4 of 4

Thread: Any tips on maxing out the RAM on an AST MegaPLUS II board?

  1. #1
    Join Date
    Mar 2015
    Location
    Bay Area, California
    Posts
    51

    Default Any tips on maxing out the RAM on an AST MegaPLUS II board?

    Hi everyone!

    I've recently been restoring / upgrading a beautiful, near-mint Compaq Portable (the original 8088-based model w/ dual floppy drives). Other than some ongoing issues with the spacebar, the machine is running beautifully from a newly-installed XT-IDE board. Along the the stock expansion boards (floppy, video), this machine also came with an AST "MegaPLUS II" board, which is a combo real-time clock + serial port + RAM expansion unit. I gather that there are other AST boards (mainly the "SixPack Plus") which are more fondly thought of, but this is what I have.

    I do see that only one out of four possible rows (or would that be "banks?") of RAM chips are installed on my AST board, as seen here. The RAM chips appear to be "D4164C" units, which seem to be still available for sale in a few places. Would adding more of these chips to the open sockets be a good idea? Are there any downsides to this? Should I just buy one of these 2meg boards from TexElec instead?

    Appreciate any tips, tricks or suggestions! I know it's not super "essential," but I do love 'maxing out' my vintage gear...

    Huxley

  2. #2
    Join Date
    May 2006
    Location
    Melbourne, Australia
    Posts
    6,720

    Default

    Quote Originally Posted by wowbobwow View Post
    I do see that only one out of four possible rows (or would that be "banks?") of RAM chips are installed on my AST board, ...
    The user's manual for the MegaPlus II card is at [here]. Figure 1.1 of that confirms that in the MegaPlus II, a horizontal row is a bank.

    Quote Originally Posted by wowbobwow View Post
    The RAM chips appear to be "D4164C" units, ...
    NEC omitted to print the prefix. The chips are actually µPD4164C.

    Quote Originally Posted by wowbobwow View Post
    ... which seem to be still available for sale in a few places.
    You have options. Section 2.5 of the manual is titled 'Installing Additional Memory on the MegaPlus II', and that section lists various RAM chips that are known to be compatible with the card.

    Quote Originally Posted by wowbobwow View Post
    Would adding more of these chips to the open sockets be a good idea?
    Each of the MegaPlus II's banks is 64 KB sized. I can see that the switch settings on your card are configuring the card to start its RAM at the 256K address mark. That suggests that there is 256 KB on the motherboard, and that the MegaPlus II is presently being used to take total conventional memory up to 320 KB (256 motherboard + 64 card).

    Assuming that there are no other RAM cards fitted (you did not mention any), then populating your card's empty 3 banks would take the conventional memory up to 512 KB (256 motherboard + 256 card). 512 KB is better than 320 KB, but maybe your planned use of the machine will not require 512 KB.

    Quote Originally Posted by wowbobwow View Post
    Are there any downsides to this?
    Well, 640 KB is more desirable than 512 KB, but maybe your planned use of the machine will not require 640 KB.

    Quote Originally Posted by wowbobwow View Post
    Should I just buy one of these 2meg boards from TexElec instead?
    That card provides expanded memory (EMS), not conventional memory. From the pointed-to website, "While this was a nice solution, you must have an application which is aware of how to use this type of RAM." I suggest that you do some research into conventional memory and expanded memory.

  3. #3
    Join Date
    Mar 2015
    Location
    Bay Area, California
    Posts
    51

    Default

    Quote Originally Posted by modem7 View Post
    The user's manual for the MegaPlus II card is at [here]. Figure 1.1 of that confirms that in the MegaPlus II, a horizontal row is a bank.


    NEC omitted to print the prefix. The chips are actually µPD4164C.


    You have options. Section 2.5 of the manual is titled 'Installing Additional Memory on the MegaPlus II', and that section lists various RAM chips that are known to be compatible with the card.


    Each of the MegaPlus II's banks is 64 KB sized. I can see that the switch settings on your card are configuring the card to start its RAM at the 256K address mark. That suggests that there is 256 KB on the motherboard, and that the MegaPlus II is presently being used to take total conventional memory up to 320 KB (256 motherboard + 64 card).

    Assuming that there are no other RAM cards fitted (you did not mention any), then populating your card's empty 3 banks would take the conventional memory up to 512 KB (256 motherboard + 256 card). 512 KB is better than 320 KB, but maybe your planned use of the machine will not require 512 KB.


    Well, 640 KB is more desirable than 512 KB, but maybe your planned use of the machine will not require 640 KB.


    That card provides expanded memory (EMS), not conventional memory. From the pointed-to website, "While this was a nice solution, you must have an application which is aware of how to use this type of RAM." I suggest that you do some research into conventional memory and expanded memory.
    This is a mind-bogglingly helpful reply, thank you! Really appreciate the time you took to break my questions down and help me unpack all of this. And yeah, you're totally right - I was a bit of a "DOS Whiz" in my youth back in the early 90's, but it's been so long since I was deep into this stuff, I've totally forgotten about the implications of "conventional RAM" vs. "expanded RAM." I'll do some more homework, and of course I'm still happy to hear from anyone else who has thoughts on this topic

    Huxley

  4. #4
    Join Date
    Mar 2015
    Location
    Bay Area, California
    Posts
    51

    Default

    Quote Originally Posted by modem7 View Post
    The user's manual for the MegaPlus II card is at [here]. Figure 1.1 of that confirms that in the MegaPlus II, a horizontal row is a bank.


    NEC omitted to print the prefix. The chips are actually µPD4164C.


    You have options. Section 2.5 of the manual is titled 'Installing Additional Memory on the MegaPlus II', and that section lists various RAM chips that are known to be compatible with the card.


    Each of the MegaPlus II's banks is 64 KB sized. I can see that the switch settings on your card are configuring the card to start its RAM at the 256K address mark. That suggests that there is 256 KB on the motherboard, and that the MegaPlus II is presently being used to take total conventional memory up to 320 KB (256 motherboard + 64 card).

    Assuming that there are no other RAM cards fitted (you did not mention any), then populating your card's empty 3 banks would take the conventional memory up to 512 KB (256 motherboard + 256 card). 512 KB is better than 320 KB, but maybe your planned use of the machine will not require 512 KB.


    Well, 640 KB is more desirable than 512 KB, but maybe your planned use of the machine will not require 640 KB.


    That card provides expanded memory (EMS), not conventional memory. From the pointed-to website, "While this was a nice solution, you must have an application which is aware of how to use this type of RAM." I suggest that you do some research into conventional memory and expanded memory.
    Hi again! Just wanted to share a quick update: thanks to your awesome info and advice, I've just completed a "DIY" RAM upgrade - I've installed ~27 new-old-stock Motorola RAM chips (purchased at a nice discount from a kind eBay vendor) and my Compaq Portable is now cheerfully reporting the exact 512k RAM amount you predicted would be the realistic maximum (for conventional RAM anyway). At last, I can run "EDIT" and some other DOS commands / apps which weren't happy with only 320k of RAM.

    Thank you again!

Bookmarks

Posting Permissions

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