Newsgroups: comp.arch,comp.sys.super,comp.parallel,comp.sys.powerpc
From: krste@ICSI.Berkeley.EDU (Krste Asanovic)
Subject: Re: Is IBM planning to discontinue POWER2 development?
Organization: International Computer Science Institute, Berkeley, CA, U.S.A.
Date: Tue, 10 Jan 1995 14:45:04 GMT
Message-ID: <3erpnk$b6d@agate.berkeley.edu>

In article <1995Jan8.184545.5581@relay.acadiau.ca>, 881045m (Richard Muise) writes:
[deleted]
> The current fastest (and currently not yet in production) PowerPC chip is the
> PowerPC 620. At 133Mhz it can issue four instructions per clock cycle, and
> has an estimated SpecInt92 of 225 (about double the POWER2) and a SpecFp92
> of 300, slightly higher than the fastest POWER2. The PowerPC is also a full
> 64-bit PowerPC implementation, which accounts for it's higher estimated
> benchmarks over the PowerPC 604, 

I'm willing to wager that being 64b didn't help it's SPEC performance
at all. In fact, if the same code was run as 64b (under some currently
hypothetical 64b PowerPC OS) I'd also wager it would run measurably
slower. Larger longs and pointers only make the memory hierarchy
perform worse.

It's higher numbers are probably due mainly to the higher clock rate
(dependent ops go faster), and perhaps to better superscalar features.

>                                  which also issues at four instructions per
> clock. The MFLOPS rating for the PowerPC 620 will be lower than the
> POWER2, due to the fact that the POWER2 has two FP units, and the 620 only
> has one. 

The POWER2 does 2 mul-adds per cycle, or 2*2*71.5 = 286MFLOPS. The 620
can do a FP mul-add every cycle, 2*133 = 266MFLOPS (I'm fairly sure
this is true for double precision). This isn't a great difference,
especially given the shorter absolute latency on the 620FPU (same
number of clock ticks (?) but shorter cycle time).

-- 
Krste Asanovic                                email: krste@icsi.berkeley.edu
International Computer Science Institute,     phone: +1 (510) 642-4274 x143
Suite 600, 1947 Center Street,                  fax: +1 (510) 643-7684
Berkeley, CA 94704-1198, USA                   http://www.icsi.berkeley.edu


