Tandy/Radio Shack TRS-80 Model 4

From: Don Maslin <donm_at_cts.com>
Date: Fri Jul 28 23:27:45 2000

On Fri, 28 Jul 2000, Ethan Dicks wrote:

> > On Fri, 28 Jul 2000, John Honniball wrote:
> >
> > > Oh, and if you try to boot a non-bootable disk, you get a
> > > nice friendly message about that disk being a data disk --
> > > now why couldn't they make it say something when there's NO
> > > disk??
> I've seen boot blocks that contain enough code to print out a message that
> you've tried to boot a data disc. Trying to boot an unformatted disk in
> such a machine will likely result in the endless seek. Eventually,

The Morrow MD-nn series had code in the boot track that would compare
the version of the EPROM with what the version of CP/M required and
either boot or post an error message.

                                                 - don

> manufacturers moved that functionality into the ROM/BIOS code, but in the
> PDP-11 days, you could boot a system by writing bits manually into
> device registers to initiate a transfer of the first part of the disk
> into low core. I used to know the exact ODT sequence to boot an RL-11
> in an 11/24 because I didn't own RL02 boot ROMs. It was about three or
> four commands. It worked because it takes a human a finite amount of
> time to enter in all the commands and that gives the drive time to read
> the block between, like, the third and fourth steps, removing the need
> to write a boot block that initiates a transfer and loops until the
> controller shows that the operation is complete.
> It all comes down to how smart you want the machine to be at boot time
> versus how flexible you want the booting scheme.
> -ethan
> =====
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Received on Fri Jul 28 2000 - 23:27:45 BST

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