Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!hplabs!hplabsz!renglish
From: renglish@hplabsz.HPL.HP.COM (Bob English)
Newsgroups: comp.arch
Subject: Re: HPE Spectrum
Message-ID: <6058@hplabsz.HPL.HP.COM>
Date: 12 Oct 90 22:14:27 GMT
References: <123093@linus.mitre.org>
Reply-To: renglish@hplabsz.UUCP (Bob English)
Organization: Hewlett-Packard Laboratories
Lines: 61

In article <123093@linus.mitre.org> jfjr@mbunix.mitre.org (Freedman) writes:
>I just learned about the HPE spectrum (64 bits address)
>in class. It apparently can run its proprietary operating
>system or unix.

Yes.  HP-PA (PA-RISC, or whatever the marketing folks are calling it
these days) supports a 64-bit virtual address space composed of 32-bits
worth of 32-bit segments.  My personal view is that the only real
difference between this segmented architecture and a flat 64-bit address
space is the size of the registers needed to support it.  In any case,
HP-PA has two types of addressing, short pointer and long pointer.  In
the long pointer case, the instruction specifies explicitly which space
register it wants to reference through.  In the short pointer case, the
space register choice is implicit on the high-order bits in the source
address.

> Is anybody out there really exercising that memory? what for?

Yes, in two ways.

In the proprietary OS (MPE-XL) all I/O is done through the virtual
memory system.  The long pointer space is used to allow large amounts of
secondary storage to be accessed.  One thing worth keeping in mind is
that this 64-bit address space is global:  A single 64-bit address is
the same in all contexts.

The machines also support short (32-bit) pointer space.  In short
pointer space, each 32-bit space is split into 4 quadrants, indexed by
the 2 high-order bits in the short pointer.  There are four space
registers available, and they can point to sequence of four spaces.
This gives the OS the freedom to run a process in four different spaces,
some shared and some private, without any modification to the user
process.  This is used a great deal by HP-UX.

Other work has been done using long pointers to support mapped files in
hp-ux similar to those used in MPE-XL.

> how does it perform?

Pretty well.  The latest processor is about 50 MIPs and over 30 SPECs.
HP-PA processors have done better in the minicomputer range than the
workstation range because the processor, cache, and chassis designs have
all been driven by that market, where the cost of the processor board
was small compared to the total system cost.  As workstation performance
begins to eat in to the commercial market, I expect that focus to change
or HP to become uncompetitive.

> As far as that machine running unix how much of the paging stuff was
> redone?

The main changes had to do with the global virtual address space.  Since
each program sees its address space as 32-bits, the part of the VM
system that manages the program's virtual address space isn't very
different.  Larger changes were required to deal with HP-PA's virtual
cache structure, which makes virtual address aliasing difficult to do
well.  The Mach port done at the University of Utah, for example, ran
about 20% slower than hp-ux because of Mach's penchant for VM aliasing.

--bob--
renglish@hplabs
HP's mouth is far too big to be filled my puny little foot.