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SubjectRe: The history of the Linux OS
In message <>, 
x Buell writes:
| On Wed, 25 Nov 1998, Brandon S. Allbery KF8NH wrote:
| > Linuxers, marred only by small issues such as (IIRC) ATI and S3 video
| > cards vs. COM4. And it's right smack in the middle of the list of
| Ah yeah, the infamous COM4 bug with S3 chipsets. Seems some fuckwit used
| the usual COM4 I/O port as one of its I/O registers. Ahh, that particular
| chipset designer should have been taken out and made to use Microsoft
| products in eternity (with a Windows 95 Beta!).

Not exactly.

The ATI and S3 chipsets started out as enhancements of IBM's 8514/A video
card. But the 8514/A was designed for Microchannel, which addresses the
entire I/O space. So the 8514/A used several registers with addresses
0xX2e8, for several values of X.

The ISA bus only has 10 I/O address lines, so I/O addresses above 0x03FF
effectively wrap around. The 8514/A ports ended up aliased to 0x02e8....

Arguably the bad design decision was to base an ISA card on the 8514/A. It
couldn't be IBM's decision because (a) there was no wraparound on
Microchannel and (b) Microchannel is perfectly capable of sharing IRQs, so
COM4 could be on IRQ3 as originally documented without conflicting with COM2
(and (c) they never intended 8514/A for use on ISA systems).

brandon s. allbery [os/2][linux][solaris][japh]
system administrator [WAY too many hats]
carnegie mellon / electrical and computer engineering KF8NH
Kiss my bits, Billy-boy.

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