Re: BOOK: OS/2 Warp Unleashed, 4th Edition cancelled

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Article #4608

#4608

From: James Knott
Date: Thu, 24 Jul 1997 00:00

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John Summerfield wrote:
> 
> In <5qvvfa$9h2@news.nternet.net>, ossi@iname.com (Doug Toltzman) writes:
> 
> ]You may be missing a critical point.  One of the reasons that Macs are friendlier
> ]is that they don't have the 8086 baggage with 16 IRQ's (of which only about 5)
> 
> The 8086 family has no such restriction: it's in the design of the
>     motherboard and the use fof PICs and how they're cascaded.
> 
> In any event, 16 (15 actually) is plenty: the AT (ISA) bus design is the
>     problem as each interrupt has to be handled before the signal can be
>     used for another interrupt.

-- 
Actually, it's worse than that.  For some stupid reason, whoever
designed the orginal PC, used rising edge triggered interupts, instead
of the usual low level triggered used elsewhere.  Because of the way
integrated circuits are built, there is a real possibility of hardware
damage, if more than one card shares an IRQ.  With low level triggered
interupts, more than one device can pull the interupt line low, using
something called "open collector output", without any problems.  With
edge triggered interupts, even if damage doesn't occur, the 2nd interupt
is lost.

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<5fcrh0$s3p@nnrp1.news.primenet.com> <5j1KzoHpvmFW092yn@skypoint.com> <5gfsb7$q8n@camel0.mindspring.com> <3337edbc.1987900@news.axion.bt.co.uk> <33329320.33D1@ibm.net> <33AC89F6.7F71@info-net.it> <5qoa91$61d$4@news1.telenordia.se> <869410485snz@deltrak.demon.co.uk> <5qvvfa$9h2@news.nternet.net> <c1.01.2Gw8XV$17q@cretin.summerfield.network>

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From: James Knott <"James Knott">
Subject: Re: BOOK: OS/2 Warp Unleashed, 4th Edition cancelled
Date: 1997/07/24
Message-ID: <33D727AC.5A32@ca.ibm.com>
X-Deja-AN: 258514081
References: <5fcrh0$s3p@nnrp1.news.primenet.com> <5j1KzoHpvmFW092yn@skypoint.com> <5gfsb7$q8n@camel0.mindspring.com> <3337edbc.1987900@news.axion.bt.co.uk> <33329320.33D1@ibm.net> <33AC89F6.7F71@info-net.it> <5qoa91$61d$4@news1.telenordia.se> <869410485snz@deltrak.demon.co.uk> <5qvvfa$9h2@news.nternet.net> <c1.01.2Gw8XV$17q@cretin.summerfield.network>
Organization: ISM Corp
Reply-To: James Knott <jknott@ca.ibm.com>
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