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From: jbs@fenchurch.MIT.EDU (Jeff Siegal)
Newsgroups: comp.sys.mac,alt.next
Subject: Re: Speed of the Next disk, what kind of network?
Message-ID: <10284@eddie.MIT.EDU>
Date: 15 Oct 88 16:31:02 GMT
References: <4XJKg9y00UgX0BFFR=@andrew.cmu.edu> <5632@hoptoad.uucp>
Sender: uucp@eddie.MIT.EDU
Reply-To: jbs@fenchurch.MIT.EDU (Jeff Siegal)
Organization: MIT EE/CS Computer Facilities, Cambridge, MA
Lines: 20

In article <5632@hoptoad.uucp> tim@hoptoad.UUCP (Tim Maroney) writes:
>It seems to me that with 8 Megs standard main memory, [...]
>just cache the entire file in RAM [...]

It is important to note that Mach does this automatically.  The Mach
group claims a significant reduction in I/O operations over 4.3 BSD
when "compiling a subset of programs in /bin"

>On thge other hand, page fault handling seems destined to be slow, unless the
>head spends all its idle time in the page swapping area automatically.

Mach doesn't have a designated swapping area like Unix does.  It just
swaps directly to the user filesystem (taking blocks away only when
needed).  An interesting question is what strategy it uses to select
blocks (i.e. layout) for this purpose.  

Anyway, as others have already pointed out, it probably isn't going to
page much with 8MB standard memory.

Jeff Siegal