🚀 go-pugleaf

In another article, gurganus@stable.ecn.purdue.edu (James P Gurganus) writes:
>sasgig@unx.sas.com (Greg Grimes) writes:
>>In an article, chandoni@husc9.harvard.edu (A Potential Security Problem) writes:
>>>
>>>Question 2:
>>>	Is there a way to boot from drive B: (on my system, a 
>>>3.5" drive) without switching the hardware? ...
>
>>PC/Computing magazine threw this question out to readers last July
>>and there were at least two answers:  (1) pull the skin off and swap
>>floppy cables (making A: B: and vice versa), or (2) there is actually
>>some software that does this you can buy.  Didn't say how.  My guess
>>is that it scrambles BIOS' ideas as to which floppy is which during
>>the boot process.
>
>I have a short program called BOOTB and all it (I think) does is put some
>information on the boot sector of a floppy that you stick in your normal boot
>drive.  The code tells the computer to get the rest of its boot code from 
>drive B.  Supposedly, its as simple as that, although I've never used it (and
>I'm not even sure I've still got it.)  I found it on a local BBS where I used
>to live, so I'm pretty sure its not commercial.  
>If I remember correctly, the documentation for it said it would work for most
>software that followed normal DOS stuff (and I really have no idea what that
>means.)   =)
>
>James Gurganus (gurganus@ecn.purdue.edu)

I wrote something similar (also called it BOOTB :-), that read the boot
sector from drive B: and executed it.  Didn't work because normal DOS
boot sector programs are hard-coded to read from A: (ROM BIOS read gets
a 0 in DL).  There's a spot in the boot sector (it's different for
different versions of DOS) that contains the code that gets splatted
in DL.  This is changed to 0x80 for hard disks.  I changed this byte to
a 1 to make the boot program read from B:.  Still didn't work.  I gave
up at that point.  If you ever try BOOTB (the one you got from the BBS :-)
and it works, I'd really like to know how.  If you send me a copy I'll
disassemble it and report.  Try it first, though, I don't think it'll
work because the problem's in the boot code on the B: drive, not the
BOOTB code in the A: drive :-)
-- 
Greg Grimes          |  "Sit down, please.  There are a thousand questions I'd
AIX Host Development |  like to ask you."   -- Prof. Jacob Barnhardt to Klaatu
sasgig@unx.sas.com   |                       ("The Day the Earth Stood Still")