Re: IIGS Memory Usage

[nathan@visi.com (Nathan Mates)]

In article <34C26B21.2EEE@mich.com>, Rich Hare  <rhare@mich.com> wrote:
>If you turn on an Apple IIGS, and don't boot GSOS or ProDos, there
>appears to be 84K of available memory marked "in use".  You can see this
>if you go to the text control panel under RAM DISK.  Subtract the 84K
>from however much you have on board (256K for a naked ROM 01, on up)

>1) Is what I am observing correct?  Am I missing something here?
>2) What is the 84K used for?  Is it Applesoft pulled out of ROM and
>stuck in RAM, or something?  If (whatever it is) is already in ROM, why
>is it stuck in RAM on startup?

   That happens here also. But, look at the line in the control panel:
'Total Free Ram'; it does not say 'Total Ram'. The GS has many parts
of memory that are essentially "free access", such as the 40/80 column
text screen. The GS's memory manager *always* marks them as used on
poweron, in order that nobody can later allocate them and and think
that data stored in them won't be toasted by anything else. [If, say,
AWGS got the text screen to store certain critical parts of your open
files, you wouldn't want something else zapping them.] This is a
safety measure that really is necessary.

   That's why some memory is always allocated, and the 'total free
ram' is a more correct statement. It's normal, it's not a
problem. When I booted my ROM 01 just now to no 5.25" disk, I had the
following allocated:

000000 Len 0800  [Text screen, various globals, etc]
00C000 Len 4800  [I/O Vectors, bankswitched memory, text screen (80 col)]
01C000 Len 4000  [I/O Vectors, bankswitched memory]
31FF52 Len 20,4,4,84 Blocks for toolsets, CDAs, etc
E0C000 Len 6000  [I/O Vectors, bankswitched memory, GS vectors]
E1C000 Len 4000  [I/O Vectors, bankswitched memory]

That's a total len of $130AC allocated or about 77996, or about 76K
reserved. [Bankswitched memory covers the ROM and the I/O space
requiring special access preventing it from being treated like normal
RAM on the GS. Thus, things like ProDOS and GS/OS hide themselves in
that space. Unswitched memory is so much nicer, but bankswitching is a
bad habit inherited from the ][+ and //e]

Nathan Mates

--
<*> Nathan Mates http://www.visi.com/~nathan/      <*>
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