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- Path: soap.news.pipex.net!pipex!usenet
- From: m.hendry@dial.pipex.com (Mathew Hendry)
- Newsgroups: comp.sys.amiga.misc
- Subject: Re: The mystery of the lost 1 Kb ChipMem
- Date: Tue, 30 Jan 96 16:34:35
- Organization: Private node.
- Distribution: world
- Message-ID: <19960130.423F88.EFDF@an184.du.pipex.com>
- References: <1551.6603T740T2708@metropolis.nl>
- NNTP-Posting-Host: an184.du.pipex.com
- X-Newsreader: TIN [AMIGA 1.3 950726BETA PL0]
-
- rbos (rbos@metropolis.nl) wrote:
- : When I type avail in the Shell I get the following output:
- :
- : Type Available In-Use Maximum Largest
- : chip 1915000 181128 2096128 1907312
- : fast 2663384 1530920 4194304 2653936
- : total 4578384 1712048 6290432 2653936
- :
- : Nothing strange here, or is there... When you check the maximum amount of
- : ChipMem availeble and divide it by 1024 (=1 Kb) you will get 2047! Since I own
- : a A1200 it should have been 2048 Kb of ChipMem, so where did that 1kB of
- : chipmem go?
- :
- : When I first noticed this it didn't bother me too much, since the remaining
- : 2047 Kb is more then enough. But when I started to think about it, I couldn't
- : think of one reasoneble explenation. Here are my theories so far...
- :
- : 1) The A1200 isn't equipped with 2048 Kb, but with 2047 Kb of chipmem on
- : the motherboard. This is highly unlikely, since I very much doubt it
- : that memorychips of 1023,5 Kb, 511,25 Kb or even 255,125 Kb exist.
- :
- : 2) The 1 Kb is always used by some strange part of the OS. Again this is
- : not very likely, because the OS uses more then one Kb and all those
- : other used Kbs can be found under the 'In-Use' colomn of avail.
- :
- : 3) The 1 Kb is always used by one or more of the custom chips. This is
- : the only reasoneble explenation, but why not show the missing 1 Kb
- : under 'In-Use' like all the other memory useage.
-
- Guess #2 is the closest; #1 and #3 are way off ;)
-
- The first 1KB "page" of RAM (from $00000000 to $000003FF) is out of bounds for
- normal programs - it stores important CPU and OS parameters - and is not
- included in the system memory list.
-
- Thus normal Chip RAM extends from $00000400 to $001FFFFF (on a machine with
- 2 Megs of Chip RAM). It is this range of memory that avail is showing you.
-
- Enforcer, a development tool, protects against access to this "zero page"
- (amongst other areas), because it is a common for buggy programs to "hit"
- this area, sometimes causing nasty crashes, due to the importance of the
- values stored there.
-
- So when you next hear the term "Enforcer hit", you'll know what it means :)
-
- -- Mat.
-