What makes a PC fast
By Brooke Crothers
Staff Writer, CNET News.com
August 5, 1999, 4:10 a.m. PT
A PC these days is defined less by the processor's raw speed and more by chip
technologies competing to rev up other parts of the PC--but it can all be pretty
confusing.
As the performance of processors from Intel and Advanced Micro Devices break through
the 600 MHz barrier, other chip technologies are stepping up to reduce bottlenecks or lift
performance, leading to a mix of solutions that can be confounding to many PC users--but
crucially important nonetheless.
The stakes are high too for companies like Rambus, Via Technologies, and ATI
Technologies as they vie to establish their technologies as the next performance
must-haves in a personal computer.
First, some questions for PC buyers to ponder. Will your PC have a 66-MHz, 100-MHz,
133-MHz, or faster, bus? Will it come with synchronous SDRAM or RDRAM? How large is
the on-chip cache? Does the graphics technology come close to true 3D performance or is
it really 2D clothed in 3D marketing hype?
Do you know what any of this means? Do you care?
Maybe you should because most of these technologies are used now--or are going into
personal computers soon--and can impact performance as much as any AMD or Intel
processor.
Pokey bus
Some of the new technologies simply try to reduce speed impediments. Two of the most
pivotal points of congestion are the system bus and main memory.
Slowdown in these two areas can be enough to make a user wonder if their Lamborgini-like
PC with a 600-MHz Pentium III isn't chained to a 1966 Volkswagen bus. "It's like you're
driving down the highway at high speed and you hit a big, deep puddle," said Nathan
Brookwood, a principal at Insight 64, a Saratoga, California-based consultancy and
formerly an executive at Micronics, a PC circuit board maker.
The problem begins at the system bus, a conduit for shuttling data between the processor
and other components like PC's main memory--and the bottleneck that is closest to the
processor.
While the processor races ahead at 500 MHz, the bus runs at a pokey 66 MHz for some
PCs. This is the case for Intel's fastest Celeron chip and similarly for the 400-MHz
Pentuim II processor used in notebooks. For faster chips, Intel, AMD, and others mitigated
this somewhat by boosting the bus speed to 100 MHz. But Brookwood cautions that for
most users the faster bus doesn't necessarily translate to a dramatic boost in system
performance. "There's something like a 3 to 5 percent difference [between 66 and 100]," he
said.
Nevertheless AMD may have the last word on the importance of bus speed. AMD's new
Athlon processor, which is due to appear in systems over the next few weeks, has a
200-MHz bus. "Athlon is clearly testing ahead of the Pentium III [in performance ]. How
much of this has to do with the bus, we don't know yet," he said.
Indeed, some analysts see the upcoming AMD bus as a very positive development. "The
[current], processor bus is contributing to the slowdown," said Mike Feibus, a principal at
Mercury Research. He said that this can cause problems for certain kinds of data
processing, particularly on a Pentium III processor running at 600 MHz with a bus running
at one-sixth the speed.
"It's like bringing a six lane highway down to one lane--depending on what time of day
you're driving," Feibus said referring to what kind of tasks the processor is working on. "If
there's a lot of traffic it can be pretty bad."
Current speed limit 133-MHz ?
This gridlock really begins to get interesting, however, when the data slams into the speed
bump lurking today in the PC's main memory. Not only is this a technical concern but also
a business battleground for companies like Via and Rambus.
"The memory is just a whole lot slower than the processor," said Brookwood who refers to
the problem as "latency." Here, data sits and goes nowhere as the memory tries to catch
up. Rambus's memory chip technology will go a long way toward reducing latency while
technology from Via is more of an interim solution, according to analysts.
So, the options boil down for the most part to this: 100-MHz memory, 133-MHz memory,
or Rambus memory, which can run at speeds ranging between 600 and 800 MHz. The
former two technologies are referred to as SDRAM and the latter as RDRAM.
Today, the faster Pentium II processors and all Pentium III processors use 100-MHz
SDRAM called PC-100. Via and others, along with a number of memory chipmakers, are
pushing to get the 133-MHz speed memory into PCs. Rambus, meanwhile, is
starting to deliver samples of its RDRAM chips but at "price premiums double or
triple [standard memory]," according to Feibus.
RDRAM can result in dramatic speed improvements but this may not happen until
processors begin to get faster, according to Brookwood. "It's very hard to assess [
Rambus] at the present time," because of lack of testing. Brookwood believes
Rambus won't really make a big difference until processors get much faster than
today's because Rambus chips can "scale" up much better to match the speeds of
superfast processors as they get speedier over time.
Intel will support Rambus with new chip technology in September. In the meantime,
the chip giant will explore the 133-MHz option but has yet to state anything definite
about an interim technology before Rambus.
So, the upshot is that faster 133-MHz memory is likely to be the solution over the
next 12 months or so for the mainstream PC market. Rambus will come later
because of current supply problems, according to Feibus.
For bus and memory constraints, almost any solution would help, according to
analysts. "[Bus and memory limitations] can be a real bottleneck for things like
streaming video," Brookwood said, an application used increasingly on the Internet.
Intel and AMD solve some potential bus and main memory limitations by increasing
the size and proximity, to the processor, of the cache, which is special memory
able to handle data in a much speedier fashion than that found in the PC's main
memory. (SDRAM, for example, is considered the main memory.) Intel, for
instance, now integrates 256 kilobytes of cache memory right onto its processors.
This is expected to increase over time, improving performance as a result.
Graphics is hot--and not a bottleneck
Graphics chips from companies such as ATI, S3, Nvidia, 3DFX, Matrox, and
NeoMagic are a boon since they take a load of the main processor and boost
performance rather than creating a bottleneck.
"Graphics is probably the one positive exception," said Feibus.
What makes graphics chips tick ? Parallelism is the esoteric but short answer. "In
summary, parallelism is certainly the most important element of graphics
architecture," said Peter N. Glaskowsky, an analyst at Microprocessor Report.
"The best chips are the ones that have the most parallel[ism]." This refers to a
chip's ability to handle a number of tasks at the same time via 'pipelines.'
"Mainstream chips from Nvidia, 3DFX, and others are at two pipelines, going to four
in their next-generation devices," he said.
But he also said that though graphics chips are generally fast, in some respects
there isn't that much difference between many of them in the mainstream PC
market. "There's no real technology advantage as such, but some chips are a little
faster than others, and some companies have done a better job with their
text-scrolling and other minor things that have a big effect on benchmarks."
He also said that the promotion of 3Dism in graphics chips is overdone. "Almost
everything we call a '3D' graphics chip really just draws 2D graphics. The 3D-ness
comes from the polygons that define the image to be drawn. They're defined in three
dimensions but projected to two dimensions during rendering--just as a camera
converts a 3D scene to a 2D film image. Even this data is really just
two-dimensional: it defines only the surfaces of objects, not what's inside them."
He said there are exceptions such as Mitsubishi's VolumePro family of chips.
See Story in Context
Related news stories
• Rambus memory expanding to servers August 4, 1999
• Intel bows to Rambus concerns July 19, 1999
• How Via, National may skirt Intel restrictions July 7, 1999
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