Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!samsung!sol.ctr.columbia.edu!emory!att!pacbell.com!pacbell!rtech!mtxinu!taniwha!paul
From: paul@taniwha.UUCP (Paul Campbell)
Newsgroups: comp.arch
Subject: Re: ACE (Was Re: Will NeXT survive?  Grow with the times?)
Message-ID: <845@taniwha.UUCP>
Date: 9 May 91 16:34:53 GMT
References: <11399@uwm.edu> <32580026@hpcuhe.cup.hp.com>
Reply-To: paul@taniwha.UUCP (Paul Campbell)
Organization: Taniwha Systems Design, Oakland
Lines: 27

In article <32580026@hpcuhe.cup.hp.com> edwardm@hpcuhe.cup.hp.com (Edward McClanahan) writes:

>Is this true?  I understand that NeXT uses a 25MHz NuBus (2.5 times the NuBus
>used in the Mac II series).  Besides, a RISC coprocessor board would primarily

No, this impression is something that Next marketting have done really well
in putting over - it's a 12.5MHz NuBus with a double clocked burst mode,
this means that for most accesses you put over it (68030s only burst
instructions and the RAM is on the motherboard, '040s require special
coding to make them burst - or alternatively you need special hardware
to support it) its only 1.25 x the speed of a normal 10MHz NuBus (in
fact the best thing you can do for the most common NuBus peripheral
(a framestore) is to reduce the single cycle latency to 2-3 clocks
a 2 clock 10MHz NuBus (200nS cycle) is much faster than a 4 clock
12.5MHz NuBus (320nS cycle)).

NuBus 90 includes the Next double clocking for bursts (they did do a good
job inimplementation) but still at 10MHz (by your standards I guess it's a
20MHz bus even though the bulk of cycles run over it will be at 10MHz).

	Paul

-- 
Paul Campbell    UUCP: ..!mtxinu!taniwha!paul     AppleLink: CAMPBELL.P

My son is now 2 months old, in that time he has doubled his weight,
if he does this every 2 months for the next year he will weigh over 300lbs.