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From: art@ACC.ARPA
Newsgroups: mod.computers.vax
Subject: uVAX-II, memory and QBUS
Message-ID: <8601281347.AA05359@ucbvax.berkeley.edu>
Date: Mon, 27-Jan-86 11:23:00 EST
Article-I.D.: ucbvax.8601281347.AA05359
Posted: Mon Jan 27 11:23:00 1986
Date-Received: Wed, 29-Jan-86 05:47:40 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: <art@acc.arpa>
Organization: The ARPA Internet
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Approved: info-vax@sri-kl.arpa


>> The uVAX-II has 8192 map regs to map the entire 4 meg (22 bit) QBUS
>> address space.  Each map reg is a longword (32 bits) and has the generic
>
>What?  If physical memory is limited to 4 meg, why is DEC selling
>8 meg boards for these machines?
>
>						-neville

The uVAX-II has a memory bus that is separate from the QBUS.  The QBUS
is limited to 4Mbytes, but the memory bus has a larger address space
(I haven't looked at the schematics to find out exactly how large).
I know DEC supports a 9Mbyte configuration.

The 8192 QBUS map regs are used to map the 4Megabyte (8192 pages) of QBUS
into the larger physical address space on the memory bus.

BTW. DEC is supposed to announce some new VAXen this week!

						Art@ACC.ARPA

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