Re: How much RAM is recognized in my Lisa?

From: James MacPhail <gg__at_email.domain.hidden>
Date: Mon, 26 Jun 2006 14:37:59 -0700

>My question is this: How can I VERIFY exactly how much RAM the Lisa
>recognizes that it has - and what the operating system and the open
>programs use of what is available?

  1. You can use the Service Mode built-in to the ROMs to check the memory size, and do your own read/write tests to confirm it (although the self-test checks it pretty thoroughly).

To enter Service Mode:

- press the space bar during the self test
- "Startup From" the floppy drive (with no floppy inserted)
- When you get the "no floppy" error, type Apple-S

The amount of memory is at location 2A8, so type this to see it:


If you have 2MB installed, the first two words of the data will be 0020 0000 (unlike intel chips, the 68K is big-endian, the high byte comes first)

2) I don't recall a 'free memory' type of display in the Lisa Office System. Recall that the LOS uses the MMU hardware to virtualize the physical memory, so "free" might be hard to define.

Given the small amount of disk space, I expect this does not use a 1:1 swap file, but instead, memory pages are dumped starting with inactive read-only code (which can just be read again when needed), and then, when necessary, open documents are auto-saved by the tool that is editing them before dumping their pages. Of course the point is that the dumped pages become free and can be reused.

In fact, the LOS seems quite memory-bound (lots of disk activity) even with the maximum RAM of 2MB, so I would expect that essentially all the memory is full, all the time. Presumably this contributes to the regal (some say glacial) speed.

HTH, James

James MacPhail                   "Think not of engineering as art,
uo957_at_email.domain.hidden                 but of art as engineering"
Sigma Seven Systems Ltd.
james_at_email.domain.hidden        <>

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