Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!ucsd!sdcc6!sdcc10!cs163afu
From: cs163afu@sdcc10.ucsd.EDU (Some call me...Tim)
Newsgroups: comp.sys.atari.st
Subject: Re: A REAL RamDisk
Summary: Reset proof, resizable--very tough
Message-ID: <92@sdcc10.ucsd.EDU>
Date: 29 Apr 89 20:42:15 GMT
References: <2963@sun.soe.clarkson.edu>
Reply-To: cs163afu@sdcc10.ucsd.edu.UUCP (Some call me...Tim)
Organization: University of California, San Diego
Lines: 43

In article <2963@sun.soe.clarkson.edu> opielask@sun.soe!clutx.clarkson.edu.UUCP writes:
>I heard there are ramdisks for the Amiga and the Mac that ajust their size
>as you put files into them.

This can't be done on the ST because of one important detail about
memory management:  When a program is executed, it is allocated ALL
available memory.  So, though you could use this from the desktop,
as soon as you were in a program that didn't give back its memory,
the RAMdisk would run out of room.

As it turns out, many programs do give back the memory--but there is
a further problem that arises:

>   Of course, unless it is reset survivable, it isn't worth it, so can't forget
>that!

The way the reset proof ramdisks work on the ST is that (I believe)
they tell the operating system that the top of memory is underneath
their lowest address, and then reset the system so that all the
system variables will be changed to reflect this.

i.e. Every time the size of the Ramdisk changes you have to reset
the computer.

Even the Amiga reset-proof-ramdisk isn't resizeable.  There are two
kinds of Ramdisks standard on the Amiga under Workbench 1.3:
resizeable, and reset-proof.

The nice thing is that you can boot from the reset-proof one (without
a floppy) under Kickstart 1.3 (a ROM upgrade).

That would be a nice feature to add to TOS...

Actually, I can imagine ways in which a reset-proof, resizable
RAMdisk might be made, but it would either require hardware
(cartridge) or TOS-version-dependant code, and the latter method may
not even be possible.

----------
Tim Mensch			| 4096 colors and 16Mhz on an ST...
Internet:  tmensch@ucsd.edu	|		Not bad.  Not bad.

Claimer:  My opinions are much more valuable than any instutions'  :->