From: belal@sco.COM (Bela Lubkin)
Newsgroups: biz.sco.general
Subject: blurry distinctions within product lines
Date: 10 Jan 93 06:42:52 GMT
Organization: [resent by] The SCOGEN gateway and Propagation Society
Resent-From: mmdf@xenitec.on.ca
Submit-To: scogen@xenitec.on.ca
Precedence: bulk

Geoffrey Welsh wrote:

> Bela Lubkin <belal@sco.COM> writes:
>
> > internal cache (partially obviated by Cyrix), the integrated FPU
> > (obviated by all the SX's & SLC's),
>
>    Cyrix' 486 chips don't have an FPU.  Mosy system diagnostics will report
> them as being 486SX chips (unless you add a Cyrix 387, in which case most
> diags think you have a 486DX).

Was that "most" or "nosy"?  ;-}

This is not surprising.  If they've done a decent job of cloning the
chip (and so far, all indications I've seen are that all of the various
386/387/486/whatever clones seem to work OK -- performance
considerations aside), it should look like what it claims to be.

> > I hate it
> > when the lines get all blurry like this...  Like, as far as I could
> > tell, at the end of it all, the difference between an IBM PC and an IBM
> > XT was the number of slots,
>
>    Aside of the physical difference, there was the BIOS support for
> installable BIOS extensions (thus making hard drive controller cards and other
> similar devices a possibility).

Bzzt -- added in a (not very much-) later version of the PC BIOS.

> > and the difference between an IBM XT and an
> > IBM AT was the height of each slot.
>
>    The AT offered cascaded interrupt and DMA controllers, and BIOS support for
> MFM hard drives.

The XT 286 broke both of these distinctions.  (Well, I don't actually
know about the cascaded interrupts, but since the XT 286 had 16-bit
slots, I don't think they could very well have left out the 2nd set of
interrupts).

> > Every other difference was broken
> > by some pair of machines ("diskless XT" broke the "XT has a hard disk"
>
>    It's not that the XT *had* a hard drive, it's that it was capable of doing
> so.

3rd parties offered hard disks for the PC, and the distinction you claim
allowed this (ability to initialize ROMs on boards in the bus) was made
available by IBM for the PC.

> > rule, "XT 286" broke the "AT has a 286, XT has an 8088" rule, etc.)
>
>    I don't believe that the XT/286 had the extra interrupts or DMA lines, but
> I'm not sure (it's been a while since I've seen one).

See above argument -- I am *NOT* speaking from knowledge here, never had
to get that involved with an XT 286, but it seems clear that if they
offered the 16-bit bus, with all its high-interrupt lines, all hell
would have broken loose if those lines were actually dysfunctional.

> > There are PS/2's with an ISA bus, so there goes another clean
> > distinction.
>
>    The PS/2 supports VGA in a system ROM at paragraph E000, while ATs need an
> extension ROM (usually at $C000).  The PS/2 BIOS will also support ESDI drives
> (rather than just 17-sector drives like the AT).

Ok, these are probably valid distinctions -- but 1) probably not what
they were thinking when they first started the PS/2 line ("Hey!  Let's
build a completely new line of computers and back them up with an
enormous ad campaign.  Their distinguishing features will be some
support code in the BIOS for enhanced video and fancier hard drives!");
2) rather esoteric; 3) certainly not reliable distinguishers between
PS/2's and other manufacturers' PC machines.

Fuzz, fuzz, blur, blur... ;-}

Next round to email, OK?  With this stuff I'm sure we *are* boring other
readers to death...  >Bela<


>   Geoffrey Welsh, 7 Strath Humber Court, Islington, Ontario, M9A 4C8 Canada
> geoff@zswamp.uucp, [xenitec.on.ca|m2xenix.psg.com]!zswamp!geoff (416)258-8467
>                 Now I've lost everything, I give to you my soul
>            And the meaning of all that I believed before escapes me
>                   In this world of none, no thing, and no one
>                             - Genesis, _Afterglow_