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From: phil@amdcad.UUCP (Phil Ngai)
Newsgroups: net.arch
Subject: Re: Paging
Message-ID: <13284@amdcad.UUCP>
Date: Tue, 7-Oct-86 20:18:42 EDT
Article-I.D.: amdcad.13284
Posted: Tue Oct  7 20:18:42 1986
Date-Received: Wed, 8-Oct-86 07:33:13 EDT
References: <8494@duke.duke.UUCP> <147@eneevax.UUCP> <7110@utzoo.UUCP> <1181@ncr-sd.UUCP>
Reply-To: phil@amdcad.UUCP (Phil Ngai)
Organization: Advanced Micro Devices, Sunnyvale, California
Lines: 41

In article <1181@ncr-sd.UUCP> greg@ncr-sd.UUCP (Greg Noel) writes:
>In article <7110@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes:
>
>>I assure you that the PDP-11 is *not* considered a virtual-memory machine,
>>not by DEC, not by anyone who knows the machine and knows what the words
>>mean.
>
>That's an awfully snippy comment.  Just because the virtual space is smaller
>than the physical doesn't mean that it isn't a virtual machine.

I think there is a confusion here on Greg's part between virtual
address space and virtual memory. No one who has studied PDP-11 memory
management will deny that some PDP-11s support virtual addressing.  In
fact, VAX stands for Virtual Address eXtension, implying that the
virtual address concept is not new to DEC's product line.  However,
this is not the same as virtual memory, as Greg seems to think.  The
VAX architecture handbook goes on to say "a virtual memory system is
used to provide a large address space while allowing programs to run
on hardware configurations that actually have smaller memory sizes."

>>Why do you think the Berkeley Unixes
>>also go by the name "VMUNIX"?  The "VM" part stands for "virtual memory",
>>which earlier Unixes -- on the 11, and on the VAX with address translation
>>but no demand paging -- were not.
>
>"You can call a tail a leg, but that doesn't make it one."
>
>(Actually, that's not quite correct, either.  Indeed, "VMUNIX" is a virtual
>memory operating system -- but then, so were the earlier ones.)

I don't see any basis at all for this claim that the earlier forms of
Unix were virtual memory operating systems. Virtual address space,
yes, for memory management is very important to a multi-tasking
operating system. But virtual memory, no.

-- 
 DIP stands for DECnet-DOS Installation Procedure.

 Phil Ngai +1 408 749 5720
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