Re: paper tape bootstraps

On Wed, 7 Sep 2011 19:06:25 -0700, "Benjamin David Lunt"
<zfysz@xxxxxxxxxxxxxxxxxxxxxx> wrote:


<ArarghMail108NOSPAM@xxxxxxxxxxxxxxxxx> wrote in message
news:373g67tjj2q0u7oekptk5c7ph5tpnc53nt@xxxxxxxxxx

Since there is a standard that the BIOS loads either a boot sector
or a MBR to 0:7C00, it follows that those programs expect to be
loaded there. (There are some old BIOSs that set the registers
wrong, so I allow for that when I write either of these routines.)

I have to ask. What registers do you think are wrong?
CS & IP, which are usually 0000 & 7C00. If not, some MBRs or boot
sectors may not work correctly.

I allow for that by doing a jmp far 0000:<next loc> which sets CS to
what I expect, assuming that I was actually loaded at 0:7C00. :-)


It is my understanding that CS:IP can be any value as long
as the pair points to the physical address of 0x07C00, and
that DL needs to be the BIOS drive value. Other than that,
nothing can be assumed.

So, in theory, only the DL value can be wrong in your statement
above, since if the CS:IP pair is wrong, your code would never
be executed to "allow for that". :-)

I am just curious to what registers you are talking about.

Ben
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