MMX-- the new standard
by Alan Zisman
(c) 1997. First
published in Canadian Computer Wholesaler, February 1997
Backward compatibility is either a blessing or a
curse? it means that
your new technology can still work with your old data, hardware, and
software.
That?s good. But it also means that you may be unnecessarily tying
yourself
to the old generation?s limitations. That can be bad.
CPU king, Intel, has been following the backwards
compatibility route
ever since the popularity of the original, 1981 IBM PC, using Intel?s
processor.
Even five generations of chips later, Intel?s x86 family of chips still
shows its ancestry. Even the limited number of new processor
instructions
included in 1985?s 80386 chip are only now being included in popular
32-bit
operating systems.
So when Intel decides to upgrade the instruction set,
the collection
of commands built into the processor, it?s news. In this case, the
result
is the MMX family of processors?replacements for today?s Pentiums and
Pentium
Pros, with new instructions optimized for multimedia. Computers
including
the first of the MMX family, the P-55C replacement for the standard
Pentium
should be just becoming available as you read this, following the
official
January 8th unveiling.
A P-55C machine will run even old applications a bit
faster than a standard
Pentium running at the same clock speed. But this modest (5- 10%) speed
increase is primarily a result of the larger, 32k Level 1 (L1) cache
built
into the new design. As well, the MMX family offers new tricks, such as
Single Instruction, Multiple Data (SIMD), which lets the CPU run
operations
in parallel. But to take advantage of these new features, software will
have to be specially written. At the moment, virtually nothing is
available
that makes full use of the MMX instruction set, but Intel claims that
properly
optimized applications will be able to provide a performance boost of
up
to 60%.
As well, while the standard, P-54C Pentiums and the
new, MMX P-55C Pentiums
are pin-compatible, you can?t simply pop the new chip into an old
motherboard?you
need control chipset (from Intel, natch), and a BIOS that?s designed
for
the new CPU. The newest motherboard and BIOS designs anticipate this,
however,
and can be set for either Pentium model.
Users of older machines need not feel left out- Intel
has announced
plans for a series of MMX Overdrive chips to upgrade original Pentiums.
Using clock-multiplying technologies, these will speed up the systems
at
the same time as adding the multimedia capabilities. These Overdrive
chips
will require an upgradeable motherboard, but will include built-in
voltage
regulators, so that they can convert older, 3.3 volt systems to the new
2.8 volt standard. The initial P-54TCB Overdrive processor will upgrade
Pentium 75, 90, and 100 mhz models to speeds ranging from 125 to 166
mhz.
Later models will be made available to upgrade more recent Pentiums to
speeds up to 200 mhz. While Intel will be making these available
through
retail channels, there are no plans to make these chips, available
later
in the first half of 1997, for OEM sales.
Further down the road are other members of the MMX
family. Intel is
planning a version to replace the current, high-end Pentium Pro,
code-named
Klamath (a river in Intel?s home state, Oregon). Klamath will debut at
233 mhz, but will entail major changes in the Pentium Pro design. The
current
processor is really two chips in a single package?the actual CPU and a
built-in Level 2 (L2) cache. Klamath will remove the L2 cache,
resulting
a chip that will sell for less, but will deliver less performance, even
with the beefed-up 32 kb L1 cache. It?s expected that the release of
Klamath
will drive down prices for P-55C machines, with these Pentium Pro
models
replacing them as entry-level machines by the end of next year. Around
the same time, look for P6T?Pentium Pro upgrade chips, expected to run
at around 300 mhz.
And following Klamath, Intel will be bringing us
Deschutes (also a river
in Oregon), a low voltage, high speed (starting at 300 mhz) processor
line
that will be aimed to mobile computing. But notebook users won?t have
to
wait until then to take advantage of MMX technology?a variety of
companies
were showing demonstration machines at last Fall?s Comdex show, running
166-200 mhz P-55C CPUs; such notebook designs should be widely
available
by mid-1997.
Intel?s rivals won?t be left too far behind, however.
Both Cyrix and
AMD have announced their own, multimedia-enhanced CPU models that will
be competitive with Intel?s designs. AMD?s K6 chip and Cyrix?s M2, for
example, will both be offering a 64 kb L1 cache, double Intel?s
offering
(and quadrupling the cache on a standard Pentium). Each will also offer
the MMX instruction set, and will be pinout compatible with standard
Pentiums,
allowing them to be usable in current motherboard designs (with
appropriate
BIOSs). The Cyrix chip will run at 2.5 volts (compared to 2.8 volts for
Intel?s design), making it potentially a contender for mobile
computers.
Intel and its competitors clearly hope that the
MMX-enabled chips will
provide next-generation power to the 80x86 family of
processors?speeding
up 3D and graphics rendering. This is vital for CAD and graphics
professionals,
and early reports suggest than an MMX processor may actually run Adobe
PhotoShop faster than current high end PowerMacs. Even more important
is
the gaming market, which drives the bulk of home purchases. Intel is
planning
to encourage manufacturers to clearly label MMX computers, and is
planning
a major advertising campaign, reminiscent of its ?Intel Inside? push.
But there is an important flaw in the MMX strategy.
When using the MMX registers of the chip, the CPU has
to turn off the
floating-point registers?both can?t be used at once. This is needed to
maintain compatibility with existing operating systems. And switching
modes
like this takes time?about 50 clock cycles. As a result, Intel suggests
that application developers refrain from using floating-point
operations
as much as possible. This, however, may prove a problem, especially
working
with 3D. (Cyrix claims that its model can switch modes in a single
clock
tick).
As well, this causes potential problems for
multitasking. Try running
an MMX-optimized graphics application and (for example), a spreadsheet
using floating-point calculations at the same time. Performance will
suffer
because of the frequent switches between floating-point and MMX modes,
but as well, the spreadsheet may end up with the wrong data, as
graphics
data mixes with its calculations. Better hope those engineers aren?t
playing
games at the same time as calculation nuclear reactor designs!
Only time will tell whether this turns out to be a
major limitation?certainly,
floating-point calculations are rarely used by most traditional
applications;
even your spreadsheet will correctly calculate your tax return without
ever once needing to use floating-point math.
Despite these potential problems, count on MMX-enabled
designs to be
the industry standards, from 1997 through to the end of the decade.