Xref: utzoo comp.unix.microport:1150 comp.unix.xenix:2866 Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!nosc!ucsd!rutgers!gatech!ncar!oddjob!gargoyle!att!chinet!mcdchg!ddsw1!karl From: karl@ddsw1.UUCP (Karl Denninger) Newsgroups: comp.unix.microport,comp.unix.xenix Subject: Re: Bell Tech Unix Review #2 Summary: Disk parameters should *NOT* be read from CMOS once POST has run Keywords: disks, poor driver design, Bell Tech, and CMOS drive types Message-ID: <1487@ddsw1.UUCP> Date: 1 Aug 88 22:46:11 GMT References: <195@focsys.UUCP> <250@belltec.UUCP> Reply-To: karl@ddsw1.UUCP (Karl Denninger) Organization: Macro Computer Solutions, Inc., Mundelein, IL Lines: 64 In article <250@belltec.UUCP> dar@belltec.UUCP (Dimitri Rotow) writes: >... >> on the disk. I'm stuck with 17. BT says I need a special rom that will >> define a drive type that has 26 sectors per track. I should by this from >> intel, they say. Intel says, "a what? never heard of it!". > >Larry, surely you know that virtually the entire PC AT world lives and dies by >the contents of the disk table in the BIOS ROM. For three years now disk >drive support for DOS and a host of other operating systems has expected an >accurate list of disk drives in the BIOS ROM ... it's a way of life in the AT >world. Yes, I know that it's neat to have an O/S that doesn't care about the >contents of the ROM (within limits), but part of the value of buying the >*right* clone is getting a well rounded disk drive table in the BIOS. Lots >of clones these days have RLL and ESDI type sectors per track in their BIOS >ROMS. Me thinks you are incorrect. First, *most* clones and Real Blue IBM Machines DO NOT have entries for RLL drives. This is because everyone and their brother does it a little differently. Some use 25 sectors per track, Adaptec uses 26, and I have also seen 27. Having ROM entries for all possibilities would exhaust the ROMs storage capacity -- and STILL be far too limited. There are new drives (and controllers) being introduced all the time. Should we have to update our ROMs every time another drive or controller hits the market? Of course not! Better machines DO know about ESDI drives -- but I've yet to run into a "mainstream" clone with RLL drives in the ROM tables. (There undoubtably are some, but none that I have seen). Even in these cases, the ESDI support I've seen does not cover the range of drives available -- you STILL need to be able to override drive types even in these machines. MSDOS uses (and always has) the (correct) BIOS calls to get disk geometry. The *ONLY* time anything should interrogate CMOS directly for drive types is on the initial POST-initiated boot sequence (ie: no code in the machine yet; this comes from the boot loader in ROM). If you're doing a direct interrogation of the CMOS, you're doing it wrong. The POST builds a disk parameter block -- which can be (and is) intercepted by controllers like the Adaptec. If you get your parameters from this RAM-based location, it is ALWAYS RIGHT providing your controller is reasonably intelligent. This is why MSDOS can run on an XT, where it still needs to know disk geometry but has not a byte of CMOS ram anywhere in the system..... SCO Xenix, MSDOS, and many others are well versed in the proper way to access disk parameters. It is *NOT* done by going through the BIOS ROM tables. These were specifically designed to be overridden if necessary. In fact, the only correct purpose of the disk type tables in ROM is to allow the system to find the boot sector on the fixed disk! Are you telling the world at large that your OS cannot deal with a drive that is not in the ROM tables? I would find that limitation immediately disqualifying for your version of UNIX (tm) -- our needs are too diverse to live with such a limitation. Of course, it does make a very good case for purchasing your hardware, doesn't it? Don't blame the hardware for what is an obvious software flaw. Fix the geometry read routine.... -- Karl Denninger (ddsw1!karl) Data: (312) 566-8912, Voice: (312) 566-8910 Macro Computer Solutions, Inc. "Quality solutions at a fair price"