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EDISK.DOC
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1989-09-17
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16-Sep-89
EDISK.DOC: Info file for my fast, small, reset-resident RAM disk (Version 2.1)
© 1988,1989 Volker A. Brandt (VBRANDT@DBNUAMA1.BITNET)
Non-profit copying and distributing permitted.
Please use this program only for humane and peaceful purposes.
EDISK is a resizeable, reset-resident RAM disk. The original idea of making
a RAM disk resident was taken from the Eternal2 program. Absolutely everything
else has changed. Therefore, I distribute this program under my name, and will
not distribute source. This is mostly to control modifications. Source is
available upon request, if you really need it.
--------------------------------------------------------------------------------
EDISK features:
- Works with 4 MB RAM. (V1.6)
- ECONF companion program configures RAM disk directly. (V1.6)
- EDISK displays a message on restart. (V1.6)
- Fast data transfer to/from even-address buffer, using "movem". (V1.8)
- 'Real' boot sector, thus enabling disk editors etc. to run. (V2.0)
- Driver fits into RAM disk boot sector, thus saving 512 bytes. (V2.0)
- Configurable size (10 to 3900 KB), 16-bit FAT for speed. (V2.0)
- 'Virtual 2nd FAT', ie. we save one FAT but pretend to have two. (V2.0)
- RAM disk volume label shows version and boot time. (V2.1)
How it works:
Simply copy EDISK21.PRG into the \AUTO folder of your boot disk (floppy or
hard disk. Copy the configuring program, ECONF21.TOS, to any directory ON THE
SAME DISK. Configure the RAM disk for your needs (see below). Then, boot the
system as you always do. You'll see the screen become white, then black again.
This is a warm reset, and it's normal. It's the way EDISK installs itself in
the system. This only happens after a cold boot.
EDISK uses exactly the amount of memory you specify. This is useful for a
number of things. Have a Mega2 and want to simulate a 1040 to test your new PD
program? Easy. Just install a 1024KB EDISK, and your Mega2 behaves like a 1 MB
machine.
Due to the 'virtual FAT trick', the RAM disk actually provides more space
than an equivalent 'real' disk.
Notes:
- EDISK must always be the first resident utility to be started. If anot er
resident program precedes EDISK after a reset and it then changes the hard-
disk vectors, EDISK changes the hard disk vectors back to the original state
before reset. The other resident program then becomes inaccessible.
- The current version of EDISK assumes that the memory to be used is zeroed
when EDISK is first installing the RAM disk. This is really only necessary
for the FAT and directory sectors.
- There is an RTS ($4E75) coded as first instruction in the boot sector. So
there is a small chance, *if* the boot sector is accidentally executed, that
the system can recover. Also, the checksum offset is set to $FFFF. Apart
from that, no special provisions are made. So, don't try to boot from this
RAM disk. :-)
- All boot sector values are correct, except the entry for 'sectors per track'
(which is set to 9 = standard for floppy disks), to minimize GEMDOS
confusion. The media byte is $F8, which is also used for some hard disk boot
sectors.
- The FAT size is optimally adjusted by the ECONF program. The FAT is always
of 16-bit type; this results in a marked GEMDOS performance increase.
ECONF, the configuration utility for "EDISK"
How it works:
Run ECONF21.TOS. It will search for EDISK21.PRG first in the current
directory, then in the \AUTO folder on the CURRENT disk (ie. the disk ECONF21
itself is run from). If it can't find EDISK21.PRG, it will complain. Once it
has located EDISK21.PRG, it will display the current settings for drive and RAM
disk, then prompt for a new drive id, and finally for a new size. After you
have entered them, the new values will be saved in the EDISK21 binary to take
effect when the RAM disk is installed.
Notes:
- The user must enter the new disk size value using ONLY digits. Anything else,
including leading and trailing blanks, will be interpreted as an illegal
entry. This isn't very 'user-friendly', but easily programmed (in assembler,
at least).
- The values for 'minsize' and 'maxsize' are arbitrary. I think 10 KB minimum
size is reasonable.
- The program may be aborted by typing ^C at the second prompt without harmful
effects.
EKILL21: The 'automatic killer utility' for "EDISK"
How it works:
Place EKILL21.PRG in the \AUTO folder of any disk you want to boot from
WITHOUT any RAM disk. If a RAM disk is found, EKILL21 will remove it from main
memory by forcing a cold boot. If no RAM disk is found, EKILL21 will display
the total amount of memory currently available. Of course, users of TOS 1.4 can
achieve the same effect by simply pressing Control-Alt-RightShift-Del ...
Notes:
- Be sure not to activate EDISK21.PRG and EKILL21.PRG at the same time. Depen-
ding on circumstances, this might cause an endless loop in the boot process.
--------------------------------------------------------------------------------
I have spent many hours on this program to make it as good as possible. It
is probably still not perfect. If you find any bugs, quirks or any other
undesirable behaviour, please notify me. I have used previous versions of these
programs since late 1987.
Finally, if you cause any harm to anyone or anything (including yourself and
your favourite data) using these programs, it's entirely your problem.
I disclaim everything, including my existence. ;-)
Volker A. Brandt
Mörikestraße 6a
D-5653 Leichlingen 1
West Germany