On Wed, 24 Nov 2010 01:10:02 +0100, Alan McKinnon wrote about Re: [gentoo-user] Boot partitions (WAS: migrating disks (from mounts to disklabels:
>Apparently, though unproven, at 01:14 on Wednesday 24 November 2010, >David W Noon did opine thusly: > >> >Errm, not exactly. SCSI/SATAs are limited to 15 (inc. one extended >> >partition) and old (legacy driven) IDEs are limited to some 63 >> >partitions if I recall correctly. If you use the new libata I think >> >you only get 15 partitions for SATA/PATA. >> >> Well that's a software limitation. I am a little surprised that >> the limit is so small, as Windows can support 24 drive letters >> (C: through Z:) assigned to hard drive partitions. Of course, >> accessing the CD-ROM would then be a bit sporty under Windows. > >Not quite, you are confused. No, you should read again what I wrote. >That's 24 'drives" of all kinds spread across all kinds: > >removeable media >hard disks (all partitions) >full disk (without partitions) >network drives >"$other_stuff" (a catchall for anything else MS might dream up). > >16 for SCSI is plenty in real life, and it's a hardware limitation not >a software one so the driver can't be updated for this. The disk hardware knows nothing about partition tables. The partition table layout used on IA32 and AMD64 hardware is a convention inherited from IBM's Industry Standard Architecture (ISA) specification and the BIOS of the PC/AT (with revisions for the PS/2, etc., plus extensions by Phoenix, AMI and Wang/Award). We still use that under Linux, some 25+ years on. Other operating systems can use radically different partition table layouts. Any disk partitioned that way -- whatever it is -- would be unreadable by Linux, Windows, OS/2 or any other OS that uses ISA assumptions. The SCSI/SATA/PATA hardware is totally agnostic about this, as it uses absolute sector addresses, without any concept of partitioning, to handle physical I/O requests. The sector address can be CHS (on older disks) or LBA, but it *never* relates to a partition, only to a complete disk. >24 drive letters has *nothing* to do with partition number limits. >They are not even vaguely related. It seems you didn't get the joke. I probably should have put a "winky" after the line ending "a bit sporty under Windows." -- Regards, Dave [RLU #314465] *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-* [email protected] (David W Noon) *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
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