Some senseless babbling from Jonathan De Boyne Pollard to Dave Davidson
on 11-17-99  10:50 about More OS/2 Questions........

 DD> AMD K6/2-350 10.3GB Seagate, all OS/2, with 96MB memory.  OS/2 only
 DD> see's 8.3GB of the drive so the other 2GB is wasted. 

 JDBP> I have a 8.49GiB (9.1GB) drive and OS/2 sees all of it just fine.  

 JDBP> The issue with drive sizes is a complex one, and I don't really have
 JDBP> the time to type in a full explanation here.  But here are two points
 JDBP> that should start you going in the right direction:

 JDBP> þ The size limits on bootable partitions are imposed by the antiquated
 JDBP> BIOS API for accessing hard discs (which is, of course, the only way to
 JDBP> access hard discs before an operating system has booted).  The absolute
 JDBP> maximum size of disc that is "visible" via the BIOS API is 1024
 JDBP> cylinders * 255 tracks * 63 sectors, which is around 7.84GiB (8.42GB). 
 JDBP> All boot files and partitions for all operating systems, or at least
 JDBP> the portions of those operating systems that are read before the
 JDBP> operating system's own disc device drivers kick in, must fit within the
 JDBP> first 1024 cylinders.   

Is there some reason that 0 is an invalid number for heads (AKA
tracks/cylinder) and sectors/track?  If there isn't, then that should be
1024*256*64, which comes out to exactly 8GiB (trying them on for size),
provided the drive uses 512-byte sectors (as almost all do these days).

Of course, that doesn't address the issue of drives larger than 8GB.

The BIOS's which are capable of supporting such drives actually support the
entire drive, through a translation scheme I have yet to find any
information about.

The normal scheme is to double the heads and half the cylinders, but that
stops working at 8GB (as it obvious).

The new BIOS's can see the entire drive as one volume.  I just don't know
how they do it.

Mike Ruskai
thannymeister@yahoo.com


... Arguing logic with a programmer can get you hexed.

___ Blue Wave/QWK v2.20
--- Platinum Xpress/Win/Wildcat5! v3.0pr2
114/477
143/1