Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!oliveb!sun!plaid!chuq
From: chuq@plaid.Sun.COM (Chuq Von Rospach)
Newsgroups: comp.sys.mac
Subject: Re: FullWrite Professional
Message-ID: <54620@sun.uucp>
Date: 26 May 88 16:08:51 GMT
References: <2730@polyslo.UUCP> <4849@ihlpf.ATT.COM> <2891@polyslo.UUCP>
Sender: news@sun.uucp
Reply-To: chuq@sun.UUCP (Chuq Von Rospach)
Organization: Fictional Reality
Lines: 28

>>What ever happenned to the concept of demand paging (virtual memory) or
>>segmented code (non-virtual memory)? 

>   Nothing, but Until the macintosh II and the 68851 most personal computers
>haven't had any sort of virtual memory like you're used to on a Larger System.

Just as a point of information, when the Macintosh was designed (and for a
few years after it had started shipping) there was NO working MMU available
for the 68xxx. Un*x systems that implemented a VM typically did it by
designing their own MMU, usually in something really neat like TTL or even
sometimes ECL. Besides being a custom hardware hack, MMU's were expensive
as all get out. 

When the Mac II first came out, the 68851 was still in short supply, as a
matter of fact, and most Mac II's didn't have them. 

To have implemented a full VM system with MMU in the original mac (remember,
the Macintosh was designed to be a single-user, single thread, 512K system
[Yes, I'm ignoring the 128K on purpose]) would have been major overkill,
added lots of complexity to the Operating system, lots of hardware to the
logic boards, and would have required adding a fan to keep the machine from
melting down. I'm pretty sure it was the latter reason why it wasn't done...
(hehe-hehe)


Chuq Von Rospach			chuq@sun.COM		Delphi: CHUQ

	Robert A. Heinlein: 1907-1988. He will never truly die as long as we
                           read his words and speak his name. Rest in Peace.