On Thu, 2008-10-16 at 05:00 -0400, Bryan J. Smith wrote: > The "root cause" is because you'all still present that old 21-bit field > of 10/6/5 (IIRC, been a bit since I looked at the spec) for cyl/hds/sec. > That's where the problems stem from, because most BIOSes of the early > 21st century used 24-bit field of 10/6/8 (IIRC, again, been a bit, but I > believe it was something of this sort) for cyl/hds/sec. That's why the > 16 heads is turned into 240, because the last three (3) bits of the > middle field (sectors) is turned into the upper three (3) bits of the > lower field of five (5) bits, when any utility goes to read eight (8) -- > when you'all only have five (5) bits for heads in your legacy 21-bit > field, instead of the eight (8) bits of virtually every other BIOS' > 24-bit field.
Okay, found a pair of pages that describe the divergence in the "grander scheme of things": http://www.pcguide.com/ref/hdd/bios/sizeGB394-c.html http://www.pcguide.com/ref/hdd/bios/sizeGB738-c.html What the article fails to note is that the great majority of vendors still use DOS/NT-based utilities to prep their disks. So we still see these limitations at sub-256 heads. I know IBM-Levono "diverged" from their BIOS upstream in the late '90s on this. I've been in and out of AMI, Award and Phoenix (Award desktop and Pheonix ServerBIOS the most), as well as the IBM-Levono. While virtually all other BIOS manufacturers solve the 256 head problem by just using 255 in an 8-bit field (1111111), IBM-Levono does this funky mess. The resulting 240 value (11110000) is completely divergent from the rest of the industry. And regardless of how/why LBA is used, the legacy geometry is still how the Legacy BIOS/DOS Disk Label (aka MBR Partition Table) is presented, the system boots and what the Legacy MS DOS MBR -- still used by NT (even Vista) -- needs. Why IBM-Levono diverged from every other BIOS vendor and their solution, I don't know. But it does get the reference as "buggy" by many of us as a result, especially since the result is a disk with geometry at odds with virtually every other vendor. -- Bryan J Smith Professional, Technical Annoyance mailto:[EMAIL PROTECTED] http://www.linkedin.com/in/bjsmith ------------------------------------------------------------- Fission Power: An Inconvenient Solution _______________________________________________ lpi-examdev mailing list [email protected] http://list.lpi.org/cgi-bin/mailman/listinfo/lpi-examdev
