Computer Processor Types
A few years ago, choosing a processor was pretty straightforward.
AMD and Intel each produced two series of processors, a mainstream line
and a budget line. Each company used only one processor socket, and
there was a limited range of processor speeds available. If you wanted
an Intel processor, you might have a dozen mainstream models and a
half-dozen budget models to choose among. The same was true of AMD.
OEM Versus Retail-Boxed
To
further confuse matters, most AMD and Intel processors are available in
two types of packaging, called OEM and retail-boxed. OEM processor
packages include only the bare processor and usually provide only a
90-day warranty. Retail-boxed processors include the processor, a
compatible CPU cooler, and a longer warranty, typically three years.
A
retail-boxed processor is usually the better deal. It typically costs
only a few dollars more than the OEM version of the same processor, and
the bundled CPU cooler is usually worth more than the price difference.
But if you plan to install an after-market CPU cooler for example,
because you are upgrading your system to be as quiet as possible it may
make sense to buy the OEM processor.
Nowadays,
choosing a processor isn't as simple. AMD and Intel now make literally
scores of different processor models. Each company now offers several
lines of processors, which differ in clock speed, L2 cache, socket type,
host-bus speed, special features supported, and other characteristics.
Even the model names are confusing. AMD, for example, has offered at
least five different processor models under the same name Athlon 64
3200+. An Intel Celeron model number that ends in J fits Socket 775, and
the same model number without the J designates the same processor for
Socket 478. A Pentium 4 processor model number that ends in J says
nothing about the socket type it is designed for, but indicates that the
processor supports the execute-disable bit feature. And so on.
AMD and Intel each offer the three categories of processors described in the following sections.
Budget processors
Budget processors
give up a bit of performance in exchange for a lower price. At any
given time, AMD or Intel's fastest available budget processor is likely
to have about 85% of the performance of their slowest mainstream model.
Budget processors are more than sufficient for routine computing tasks.
(After all, today's budget processor was yesterday's mainstream
processor and last week's performance processor.) Budget processors are
often the best choice for a system upgrade, because their lower clock
speeds and power consumption make it more likely that they'll be
compatible with an older motherboard.
AMD Sempron
The various models of the AMD Sempron processor
sell in the $50 to $125 range, and are targeted at the budget through
low-end mainstream segment. The Sempron replaced the discontinued Socket
A Duron processor in 2004, and the obsolescent Socket A Athlon XP
processor in 2005. Various Sempron models are available in the
obsolescent Socket A and in the same Socket 754 used by some Athlon 64
models.
AMD actually packages two different processors under the Sempron name. A Socket A Sempron, also called a K7 Sempron, is in fact a re-badged Athlon XP processor. A Socket 754 Sempron, shown in Figure 5-1 is also called a K8 Sempron,
and is really a cut-down Athlon 64 model running at a lower clock speed
with a smaller L2 cache and a single-channel memory controller rather
than the dual-channel memory controller of the Athlon 64. Early Sempron
models had no support for 64-bit processing. Recent Sempron models
include 64-bit support, although the practicality of running 64bit
software on a Sempron is questionable. Still, like the Athlon 64, the
Sempron also runs 32-bit software very efficiently, so you can think of
the 64-bit support as future-proofing.
Figure 5-1: AMD Sempron processor (image courtesy of AMD, Inc.)
If
you have a Socket 462 (A) or Socket 754 motherboard in your system, the
Sempron offers an excellent upgrade path. You'll need to verify
compatibility of your motherboard with the specific Sempron you intend
to install, and you may need to upgrade the BIOS to recognize the
Sempron.
Intel Celeron
For many years, the Intel Celeron processor
was the poor stepsister, offering too little performance at too high a
price. Cynical observers believed that the only reason Intel sold any
Celeron processors at all was that system makers wanted the Intel name
on their boxes without having to pay the higher price for an Intel
mainstream processor.
That all changed when Intel introduced
their Celeron D models, which are now available for Socket 478 and
Socket 775 motherboards. While Celeron D models are still slower than
Semprons dollar-for-dollar, the disparity is nowhere near as large as in
years past. Celeron D processors, which sell in the $60 to $125 range,
are very credible upgrade processors for anyone who owns a Socket 478 or
Socket 775 motherboard. Like the Sempron, Celeron models are available
with 64-bit support, although again the practicality of running 64-bit
software on an entry-level processor is questionable. Once again, it's
important to verify the compatibility of your motherboard with the
specific Celeron you intend to install, and you may need to upgrade the
BIOS to recognize the Celeron.
AVOID NON-D CELERON PROCESSORS
Celeron
processors (without the "D") are based on the Northwood core and have
only 128 KB of L2 cache. These processors have very poor performance,
and unfortunately remain available for sale. The Celeron D models are
based on the Prescott-core, and have 256 KB of L2 cache.
Mainstream processors
Mainstream processors
typically cost $125 to $250 although the fastest models sell for $500
or more and offer anything up to about twice the overall performance of
the slowest budget processors. A mainstream processor may be a good
upgrade choice if you need more performance than a budget processor
offers and are willing to pay the additional cost.
However,
depending on your motherboard, a mainstream processor may not be an
option even if you are willing to pay the extra cost. Mainstream
processors consume considerably more power than most budget processors,
often too much to be used on older motherboards. Also, mainstream
processors often use more recent cores, larger L2 caches, and other
features that may or may not be compatible with an older motherboard. An
older power supply may not provide enough power for a current
mainstream processor, and the new processor may require faster memory
than is currently installed. If you intend to upgrade to a mainstream
processor, carefully verify compatibility of the processor, motherboard,
power supply, and memory before you buy the processor.
AMD Athlon 64
The AMD Athlon 64 processor, shown in Figure 5-2,
is available in Socket 754 and Socket 939 variants. As its name
indicates, the Athlon 64 supports 64-bit software, although only a tiny
percentage of Athlon 64 owners run 64-bit software. Fortunately, the
Athlon 64 is equally at home running the 32-bit operating systems and
applications software that most of us use.
Figure 5-2: AMD Athlon 64 processor (image courtesy of AMD, Inc.)
Like
the Sempron, the Athlon 64 has a memory controller built onto the
processor die, rather than depending on a memory controller that's part
of the chipset. The upside of this design decision is that Athlon 64
memory performance is excellent. The downside is that supporting a new
type of memory, such as DDR2, requires a processor redesign. Socket 754
models have a single-channel PC3200 DDR-SDRAM memory controller versus
the dual-channel controller in Socket 939 models, so Socket 939 models
running at the same clock speed and with the same size L2 cache offer
somewhat higher performance. For example, AMD designates a Socket 754
Newcastle-core Athlon 64 with 512 KB of L2 cache running at 2.2 GHz a
3200+ model, while the same processor in Socket 939 is designated an
Athlon 64 3400+.
NUMBERS LIE
The
model numbers of Athlon 64 and Sempron processors are scaled
differently. For example, the Socket 754 Sempron 3100+ runs at 1800 MHz
and has 256 KB of cache, and the Socket 754 Athlon 64 2800+ runs at the
same clock speed and has twice as much cache. Despite the lower model
number, the Athlon 64 2800+ is somewhat faster than the Sempron 3100+.
Although AMD hotly denies it, most industry observers believe that AMD
intends Athlon 64 model numbers to be compared with Pentium 4 clock
speeds and Sempron model numbers with Celeron clock speeds. Of course,
Intel also designates their recent processors by model number rather
than clock speed, confusing matters even further.
Intel Pentium 4
The Pentium 4, shown in Figure 5-3,
is Intel's flagship processor, and is available in Socket 478 and
Socket 775. Unlike AMD which sometimes uses the same Athlon 64 model
number to designate four or more different processors with different
clock speeds, L2 cache sizes, and sockets Intel uses a numbering scheme
that identifies each model unambiguously.
Older Pentium 4 models,
which are available only in Socket 478, are identified by clock speed
and sometimes a supplemental letter to indicate FSB speed and/or core
type. For example, a Socket 478 Northwood-core Pentium 4 processor
operating at a core speed of 2.8 GHz with the 400 MHz FSB is designated a
Pentium 4/2.8. The same processor with the 533 MHz FSB is designated a
Pentium 4/2.8B, and with the 800 MHz FSB it's designated a Pentium
4/2.8C. A 2.8 GHz Prescott-core Pentium 4 processor is designated a
Pentium 4/2.8E.
Figure 5-3: Intel Pentium 4 600 series processor (image courtesy of Intel Corporation)
Socket
775 Pentium 4 models belong to one of two series. All 500-series
processors use the Prescott-core and have 1 MB of L2 cache. All
600-series processors use the Prescott 2M core and have 2 MB of L2
cache. Intel uses the second number of the model number to indicate
relative clock speed. For example, a Pentium 4/530 has a clock speed of 3
GHz, as does a Pentium 4/630. The 540/640 models run at 3.2 GHz, the
550/650 models at 3.4 GHz, the 560/660 models at 3.6 GHz, and so on. A
"J" following a 500-series model number (for example, 560J) indicates
that the processor supports the XDB feature, but not EM64T 64-bit
support. If a 500-series model number ends in 1 (for example, 571) that
model supports both the XDB feature and EM64T 64-bit processing. All
600-series processors support both XDB and EM64T.
Extreme Processors
We
classify the fastest, most expensive mainstream processors those that
sell in the $400 to $500 range as performance processors, but AMD and
Intel reserve that category for their top-of-the-line models, which sell
for $800 to $1,200. These processors the AMD Athlon 64 FX, the Intel Pentium 4 Extreme Edition, and the Intel Pentium Extreme Edition
are targeted at the gaming and enthusiast market, and offer at best
marginally faster performance than the fastest mainstream models.
In
fact, the performance bump is generally so small that we think anyone
who buys one of these processors has more dollars than sense. If you're
considering buying one of these outrageously expensive processors, do
yourself a favor. Buy a $400 or $500 high-end mainstream processor
instead, and use part of the extra money for more memory, a better video
card, a better display, better speakers, or some other component that
will actually provide a noticeable benefit. Either that, or keep the
extra money in the bank.
Dual-core processors
By
early 2005, AMD and Intel had both pushed their processor cores to
about the fastest possible speeds, and it had become clear that the only
practical way to increase processor performance significantly was to
use two processors. Although it's possible to build systems with two
physical processors, doing that introduces many complexities, not least a
doubling of the already-high power consumption and heat production.
AMD, later followed by Intel, chose to go dual-core.
Combining
two cores in one processor isn't exactly the same thing as doubling the
speed of one processor. For one thing, there is overhead involved in
managing the two cores that doesn't exist for a single processor. Also,
in a single-tasking environment, a program thread runs no faster on a
dual-core processor than it would on a single-core processor, so
doubling the number of cores by no means doubles application
performance. But in a multitasking environment, where many programs and
their threads are competing for processor time, the availability of a
second processor core means that one thread can run on one core while a
second thread runs on the second core.
The upshot is that a
dual-core processor typically provides 25% to 75% higher performance
than a similar single-core processor if you multitask heavily. Dual-core
performance for a single application is essentially unchanged unless
the application is designed to support threading, which many
processor-intensive applications are. (For example, a web browser uses
threading to keep the user interface responsive even when it's
performing a network operation.) Even if you were running only
unthreaded applications, though, you'd see some performance benefit from
a dual-core processor. This is true because an operating system, such
as Windows XP, that supports dual-core processors automatically
allocates different processes to each core.
AMD Athlon 64 X2
The AMD Athlon 64 X2, shown in Figure 5-4,
has several things going for it, including high performance, relatively
low power requirements and heat production, and compatibility with most
existing Socket 939 motherboards. Alas, while Intel has priced its
least expensive dual-core processors in the sub-$250 range, the least
expensive AMD dual-core models initially sold in the $800 range, which
is out of the question for most upgraders. Fortunately, by late 2005 AMD
had begun to ship more reasonably priced dual-core models, although
availability is limited.
Figure 5-4: AMD Athlon 64 X2 processor (image courtesy of AMD, Inc.)
Intel Pentium D
The
announcement of AMD's Athlon 64 X2 dual-core processor caught Intel
unprepared. Under the gun, Intel took a cruder approach to making a
dual-core processor. Rather than build an integrated dual-core processor
as AMD had with its Athlon 64 X2 processors, Intel essentially slapped
two slower Pentium 4 cores on one substrate and called it the Pentium D dual-core processor.
The 800-series 90 nm Smithfield-core Pentium D, shown in Figure 5-5,
is a stop-gap kludge for Intel, designed to counter the AMD Athlon 64
X2 until Intel can bring to market its real answer, the dual-core 65 nm
Presler-core processor, which is likely to be designated the 900-series
Pentium D. The Presler-based dual-core processors will be fully
integrated, compatible with existing dual-core Intel-compatible
motherboards, and feature reduced power consumption, lower heat output,
twice as much L2 cache, and considerably higher performance.
Figure 5-5: Intel Pentium D dual-core processor (image courtesy of Intel Corporation)
Reading
the foregoing, you might think we had only contempt for the 800-series
Pentium D processors. In fact, nothing could be further from the truth.
They're a kludge, yes, but they're a reasonably cheap, very effective
kludge, assuming that you have a motherboard that supports them. We
extensively tested an early sample of the least expensive 800-series
Pentium D, the 820. The 820 runs at 2.8 GHz, and under light, mostly
single-tasking use, the 820 "feels" pretty much like a 2.8 GHz
Prescott-core Pentium 4. As we added more and more processes, the
difference became clear. Instead of bogging down, as the single-core
Prescott would have done, the Pentium D provided snappy response to the
foreground process.
