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Date   : Thu, 06 Apr 1989 19:16:41 GMT
From   : vsi1!wyse!mips!prls!philabs!linus!alliant!merk!spdcc!ima!cfisun!lakart!uucp@apple.com (comp.os.cpm gateway)
Subject: adding a hard disk to your floppy-only system

rusty@cadnetix.com asks:
> Has anyone else added a hard disk to a CP/M system which was not
> originally configured for a hard disk?  Can I do the trick that
> Kaypro did and boot from either flops or hard?  Any words of
> wisdom? (Other than "Don't do it!" :-)

I can only speak of my case with a Televideo TS803 from a semi-hypothe-
tical point of view.

The story - I have a TS803 (non hard disk version) and I added a
mini-winnie hard disk to it. So in response to your first question I
have added a hard disk to a floppy only system. To explain what is
necessary: all you have to do is to make the BIOS know about the
hard disk - add the necessary tables, and the code to read / write
it, and you can run from the hard disk.

That part is done, and works - i.e. I have a system with the original
floppies, and a hard disk "grafted" on.

As to booting it: I don't know how you work, but the boot process in
the 803 goes like this:

The boot rom reads drive A:, Track 0, Sector 0 into ram at a particular
spot, then jumps to that code. So I can put any bootstrap loader I like
into that 256 bytes of code - as it is, I just read the operating system
from the remainder of track 0 and track 1, and jump to the cold boot entry
point of the BIOS.

Assuming you work like this, if you can read and write the hard disk OK,
it can be done as a two step operation. Firstly write a boot sector
loader that will be pulled from floppy by the boot rom, that loads CCP /
BDOS / BIOS from the hard disk, and save that onto a floppy. Now when you
boot that floppy, the boot sector (T 0 S 0) comes off the floppy, drops into
ram, and is executed, but it goes to the hard disk to get the rest of
the operating system. Next step is to write this same boot sector somewhere
on the hard disk, and (here comes the hard part :-) ) modify the boot
rom to read from the hard disk. I plan to go about doing this for my
system in the above manner, and also plan to arrange that the rom looks
first to see if a floppy is present: if so boot from it. If not it then
looks at the hard disk to see if it can find anything there. So if I
reset with a floppy in drive A: I'll boot from the floppy, otherwise I'll
boot from the hard disk.
       dg@pallio.UUCP - David Goodenough               +---+
                                               IHS     | +-+-+
       ..... !harvard!xait!lakart!pallio!dg            +-+-+ |
AKA:   dg%pallio.uucp@cfisun.cfi.com                     +---+

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