Date: Thu, 23 Mar 1995 01:33:38 -0800 (PST) From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> To: bde@zeta.org.au (Bruce Evans) Cc: PVinci@ix.netcom.com, hackers@FreeBSD.org Subject: Re: ata/ide sector translation modes c/h/s vs. LBA? Message-ID: <199503230933.BAA12284@gndrsh.aac.dev.com> In-Reply-To: <199503230647.QAA04580@godzilla.zeta.org.au> from "Bruce Evans" at Mar 23, 95 04:47:34 pm
next in thread | previous in thread | raw e-mail | index | archive | help
> > >> Why does the ATA standard make such a big stink about LBA mode?? > > >Because it is *new*, and allows you to use drives >536870912 bytes. > > No. Even the old ATA standard specifies addressing drives with > 65535(+1?) * 16 * 255 sectors (almost 128GB). LBA only increases > the limit to 65536 * 16 * 256. See > "Yet Another ATA-2/Fast-ATA/EIDE FAQ" in > comp.sys.ibm.pc.hardware.storage. Yes, your right, the ATA spec does increase it to 16 bits for cylinder, it's DOS that still has lots of braindamage in this area (fdisk). > >It greatly simplifies the calculation for this. Basically a drive > ^slightly Hummm... conversion of DOS block offset to cyl/head/sector with non-LBA requires division and mod operators. With LBA it is simple OR's and SHIFTS. Also you don't have to do all the funky bit stuff for the C/H/S format, or do you still have to do that, I thougt not. > >in LBA mode has 256 sectors, 16 heads and upto 1024 cylinders. > > Up to 65536 or 65536 cylinders. Oops, in previous mail I said that LBA > addresses are 24 bits. They are actually 28 bits (4 more in the old > head bits). The bits are rearranged (the head bits become bits 24-27 > of the LBA, and the braindamaged 1-based sector numbers are gone), so > it is only a heuristic to think of the translation as giving a 256S * 16H > geometry. Humm... more than SCSI (24) :-) -- Rod Grimes rgrimes@gndrsh.aac.dev.com Accurate Automation Company Custom computers for FreeBSD
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199503230933.BAA12284>