Roy J. Tellason wrote to Charles Gaefke on 04-29-1998
RT> I wonder why they decided that the initial loading had to 
RT> be done by the BIOS code?  There's probably a good reason 
RT> for that design choice,  but it's not apparent to me.
Some of us 'old timers' have some interesting tales re: bootstrap -
which is what the initial startup really is.  You have some limited
amount of generic functionality built into the machine.  In the case of
the PC, that's the BIOS.  It's barely smart enough to pick a device and
read cylinder (track) 0, head 0, sector 1 (which is the first sector
but they start that at 1 for some reason lost in the dim, dark past). 
It knows just enough to read 512 bytes to a predefined location in
memory, then transfer control to a specific location in that memory. 
That's it - no more, no less.  Notice that there is no mention of a
file or file system - just a raw read of a specific disk sector.  Now
you have a small program in memory and IT knows just enough to locate
the next bit of info to read.  It may even be smart enough to be able
to find a file by name for a specific OS format, but that's it.  So you
load a bit larger program which can do even more.  Pretty soon you have
the OS in the system and you are off and running, but the initial steps
depend on some non-volatile code segments that literally pulls the
system up by it's bootstraps.
To date myself, the boot process on the first computer I ever got my
hands on physically was an SDS4000 - all of 8k of 24 bit core memory,
not bad.  It had reasonably smart channel controllers that could read a
block of data from the start of a tape.  To boot, you set 24 toggle
switches to issue the channel command to read the first block of data
when you stepped the computer, then you had to toggle in another
instruction to make ther computer go to the proper address in that
block to start the rest of the process that pulled that machine 'up by
it's bootstraps'.  There was a similar setup on the first generally
available micros, the old Altairs.
Computers suffer severe memory problems - they remember NOTHING when
power goes off.  You have to re-educate them every time you power up. 
This, BTW, ignores the case where the entire OS is in ROM and always
ready to go (bet you never heard of OS/2 on EPROMS, but it's there!).
Will Honea 
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