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POWERPC 603E - NOT *JUST* BIGGER CACHES AND A FASTER CLOCK

(February 17th 1995) The more you look at the PowerPC 603e, running
at 100MHz, the more it looks like the natural successor to the 601 at
the low end of the desktop. It's likely to be cheaper, it's very
nearly as fast and it has a lot more headroom.

In order to get the 601 up to 100MHz, IBM needed to move to a whole
new process. While it used 0.5 micron CMOS, the company introduced a
new transistor geometry which allowed it to cram the components onto
a smaller die-size. So dramatic was this shrinkage that the 100MHz
601 became physically smaller than the 603 despite its much higher
transistor count. When asked why the new 603e doesn't use the same
process, IBM and Motorola reply quite simply that they could achieve
100MHz using the older technology so they are keeping the new stuff
in reserve for the higher clock speeds.

As expected, the gross structure and capabilities of the 603e is
essentially the same as the older 603, but there are a few nips and
tucks worth noting. Several logic-paths have been re-written to
achieve the 100MHz clock-speed and it's not just the cache's size
that has been increased, so has its performance; the 603e cache is
four-way associative, compared with two-way.

The new processor's load/store unit has also been tweaked, so that
any stores that hit the cache only take one cycle where previously
they took two, and mis-aligned accesses are also handled better -
improvements that have incidentally been carried across to the new
PowerPC 602.

>From Apple's point of view teh extra cache is the most obvious boon,
since its current 68k emulator technology needs lot of cache elbow
room, however, the Power PC603e also introduces the ability to run
the chip at fractional speeds comparitive to the machine's bus and
this will give Apple the flexibility to ship a range of PowerPC
Powerbooks with differential clock speeds, as well as easing its task
of getting upgrade boards out for the existing Powerbooks and Duos.

In our Powerflash on Monday we questioned why the SPECint figures of
the 603e were marginally better than the 100MHz 601, while the
floating point figures were marginally worse. IBM Microelectronics
PowerPC product line marketing manager David Ryan says the 601's
unified 32k cache suits the cache-hungry floating point tests better
than the 603e's 16k instruction cache. The integer tests, on the
other hand, reflect the 603e's cleaner design.

The general shape of the low-end PowerPC market will now depend
almost entirely on how the companies decide to price the new part,
and the proportion of the initial production run that gets swallowed
by Apple Computer. Integer performance is still the key to fast
machine performance with most applications, and the 603e beats the
601 there. Similarly, the 603 is significantly cheaper than the 601,
and although the 603e is bigger than the older model, it should still
be cheaper to fabricate than the 601. This is probably the beginning
of the end for the 601.

 

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