Re: Hey old people

[Drsolly <drsollyp () drsolly com>]

On Wed, 21 Dec 2005, Blue Boar wrote:

> Drsolly wrote:
> > The original PC Bios didn't have hard disk code, so you had to attach the 
> > HD via a device driver. That meant that you couldn't boot from the hard 
> > disk. I actually had one, it was a 10 mb monster from Xebec, costing 
> > £1000. So, since booting from a floppy was the only way to start up the 
> > computer, I wouldn't call it a vulnerability that there was no way to 
> > change that.
>
> None of them had HD BIOS code.  They had hooks that would allow the 
> add-on card to get its ROM into the POST sequence.  That's what the 
> whole Debug: G=C800:5 business to do low-level formats was about, you 

I think that was particular to the WD HD controllers.

> had to talk to the controller BIOS.

Maybe the original PC didn't do a rom scan?
 
> Hm... this is hurting my brain.. I guess it was the AT that was the 
> first machine that had HD Types, and was HD-aware?

Yes
 
> The 5150A was missing the hook code, as well as the ability to go past 
> 576K physical RAM.

There was a way to go past it, though. I had one of those, and I used 
640kb of main memory, plus another 192kb up in rom space, used as a 
ramdisk.
 
> I suppose if you want to get silly about it, I also did at least one 
> 5150A BIOS upgrade which fixed both those problems, effectively making 
> it a B.
>
> > I actually used DOs 1.1, I don't remember whether EXEs were available or 
> > not. Are you sure they weren't? It would have meant a severe restriction 
> > on the size of programs, and I don't recollect this.
>
> I'm not 100% sure that's correct, it was a long time ago. :)  Actually, 
> I never used anything before 2.11(?) significanly myself.  I used 1.0 
> for like 10 minutes one day, and then sold it to a collector.  I thought 
> the major features of 2.0 were heirarchical directories, upgrading from 
> FAT10 to FAT12?, and the introduction of .exes, being the first 
> non-directly mapped executable format for DOS, an upgrade to the old 
> CP/M .com files.  I know you couldn't really use a HD before DOS 2.0.
>
> > Dos 2.0 was multiprocessing.
>
> Introduction of the TSR hooks?

Right.
 
> It's still missing the memory protection/supervisor mode.
 
You couldn't do that on an 8086.


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