Newsgroups: comp.os.minix
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From: cwr@crash.cts.com (Will Rose)
Subject: Re: bios vs ps HD drivers
Organization: CTS Network Services (CTSNET), San Diego, CA
Date: Wed, 5 Jul 1995 05:55:02 GMT
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raduga@netcom.com wrote:
: okay!
: I've finally gotten it to boot my PS/2 model 50, 
: with 'hd=bios' using the bios driver, and
: 'hd=ps' for the PS/2 driver, and on bootng it seems 
: to recognise the *drive* at least.

Glory Glory Glory!!!

: However, when i try to mount /dev/hd2 (my minix partition)
: it (the ps driver) claims that its an invalid filesystem on there.

Boo.

: when i try to mkfs with the ps driver, it fails too.

Hiss.

: The BIOS drivers offer no trouble at all.
: Is there any reason why i *should* be using the PS drivers anyway?
: are they faster than the generic BIOS? (less ram intensive?)
: Is there something about the 20meg drive in the old PS/2-50
: that its geometry is nonstandard, and needs to be accounted for?

The disadvantage of the bios drivers is that you are stuck in real
mode, which limits your access to  memory.  I once did some tests
on an early Minix 1.5 driver (no relation to the current driver 
code) and found < 5% difference between scsi_wini and bios_wini in
real mode.  I'd guess the present drivers are the same, but I've not
run the tests.

: note: the BIOS driver apon boot sees 610 cylinders,
: 4 heads, 17 sectors;  the PS driver finds 611 cylinders
: (and probably is guessing wrong)

This might be eg: a systems track.  I seem to remember some of
the PS/2s using the HD for some system info.  What you do about
that I've no idea.

: is there a way to override the geometry sensing?

Hack the driver.

: (sigh. i think im getting closer :)

: also, regarding REAL vs PROTECTED mode,
: are there any significant advantages to running
: in 286 protected mode, over real?  
: other than having the extra memory and all...

: (i know wind0ze exhibits major system differences 
:  between the two modes, but all the other intel multitasking
:  OSes ive used were 386 based, which is an altogether different
:  form of protected mode operation)

The 286/386 differences aren't really a factor: in Minix, you never
have to switch back to real mode as MSDOS has to -  you go into
protected mode at boot up, or shortly afterward, and stay there.  
That's why bios_wini won't work - it's a real mode driver.

: ha. i know there *should* be advantages, but what are they?

Memory, memory and memory.  Minix has got noticeably fatter over 
the years (the 1.3 kernel was ~120Kb, and 1.7 is ~190Kb) and its
getting harder to run a useful number of processes in the 640KB
of real mode, especially since it's also convenient to have the
root file system in RAM.  With 32-bit protected mode and 4MB of
RAM you have 'as much memory as anyone will ever need'.

Will
cwr@crash.cts.com

