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From: ron@topaz.rutgers.edu (Ron Natalie)
Newsgroups: comp.unix.questions
Subject: Re: Vax processors
Message-ID: <13413@topaz.rutgers.edu>
Date: Mon, 20-Jul-87 20:33:05 EDT
Article-I.D.: topaz.13413
Posted: Mon Jul 20 20:33:05 1987
Date-Received: Wed, 22-Jul-87 01:58:16 EDT
References: <138@bernina.UUCP>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 49
Keywords: Vax, CPU, Speed


	What are the CPU's in the following computers:
	PDP-11/45
	Vax 11/750, Vax 11/780,	Vax 11/785
	Vax 8600

Those machines refer to specific computers made by Digital Equipment
Corporation.

The PDP-11/45 is a specific model of the PDP-11 processor.  The CPU
is commonly referred to as the PDP-11/45 CPU (although it does have
some other name as well like K?-11).  Like others of the PDP-11 family,
it has the basic PDP-11 instruction set.  It supports Kernel, Supervisor,
and User mode (each with their own memory management registers) and up
to 256 Kbytes of memory.  It uses the DEC UNIBUS (also being the finest
implementation of that bus) for I/O.  It is differentiated from most others
in the PDP-11 line by having SPLIT-Instruction and Data Address maps.  It
was near the top of the line (second only to the PDP-11/70, which supported
4 meg of memory and had the capability of using MASSBUS peripherals).
This machine is very old

The VAX 11 is the follow on to the PDP-11 line.  VAX stands for Virtual
Address Extension.  Unlike their predecessors, they did paging and supported
32 bit addressing.  The CPU in the 750 was about a third the speed of the
780.  The 780 is usually the basic unit of compute speed (having been a
common computer that had a processor speed very close to the mythical MIPS).
While the 750 and the 780 used different CPU buses (the CMI and SBI
respectively), they both had interfaces to connect MASSBUS's and UNIBUS's.
These machines are contemporary to each other and were introduced in the
late seventies.  One other CPU, the 730, was also available, this was again
a third as slow as the 750 and was hence pretty unusable (it supported UNIBUS
only).

The 782 was DEC's composition of two 780's and a shared memory controller.
One CPU was the master and had all the peripherals.  One could get about
a 70% speed up for a lot of money.  Purdue University found that there was
plenty of bandwidth left on the SBI, so they removed the terminator and
installed a second 780 CPU in its place for a comparable speedup for much
less money than a 782.

The 785 is essentially a fast CPU upgrade for the 780 CPU yielding a 70%
speed-up.  Everything else was the same.  This was an easy way for people
stuck with 780's to get some extra performance since DEC was getting behind
the industry with their new machine.

The 8600 is one of the new VAX products.  The bus changed again (now called
BI) and the box is generally much better mechanically.

-Ron