PC Hardware in a Nutshell, 3rd Edition [Electronic resources] نسخه متنی

4.5 Forthcoming AMD and Intel Processors

Intel and AMD constantly strive to out-do each other in bringing
faster and more capable processors to market. In late 2003 and into
2004, each company will be ramping up its new-generation desktop
processors. Although the current Athlon XP and Pentium 4 processors
will continue to sell in large numbers throughout 2003 and into 2004,
the future definitely belongs to these new processor lines. AMD hopes
to get a foothold in the corporate market and to increase their
general market share with their new desktop processors, but Intel has
some plans of its own to protect its 80%+ general market share and
its nearly 100% corporate market share.

As we write this in July 2003, only the Opteron processor is shipping, and only in limited numbers. The Athlon 64 and the Prescott/Pentium 5 are not yet shipping and we have been unable to get pre-production samples from AMD and Intel. Accordingly, much of this section is speculative, based on published information that is subject to change, industry rumors, and informed speculation. However, we thought it worthwhile to include the best information we had available as we went to press, because even imperfect or incomplete information may be useful to our readers.

4.5.1 AMD Opteron and Athlon 64

By mid-2002, AMD was struggling to produce Athlons that could match
Pentium 4 performance. By July 2003, it was obvious to nearly
everyone that the Athlon XP had reached the end of the line and that
the 3200+ would almost certainly be the final Athlon XP processor.
AMD was able to push the Athlon core further than anyone expected,
eventually reaching a core clock speed of 2.2 GHz in the Barton-core
Athlon XP 3200+ model. AMD also expanded L2 cache from 256 KB on
earlier cores to 512 KB on the Barton core, and increased FSB speeds
from 266 MHz to 333 MHz and eventually to 400 MHz on the final Athlon
XP models.

But all of these enhancements yielded only marginal performance
improvements over earlier Athlon models. The real problem was that
the Athlon core itself had reached its limits, while
Intel's Pentium 4 core wasn't even
breathing hard. AMD badly needed an entirely new processor core if
they were to compete with Intel on anything like a level playing
field.

In April 2003, AMD shipped their new-generation processor, code-named
K8 or Sledgehammer, officially named Opteron, and ironically dubbed
"Lateron" by pundits because of the
repeated and lengthy delays AMD suffered in bringing this processor
to market. (Nor is AMD alone in having evil nicknames applied to its
processors. Some wags called the original Itanium 1 the
"Itanic" because, like its
namesake, it sank without a trace.)

AMD will produce two processor lines based on the K8 core. The
Opteron is intended for servers, and began shipping in April 2003.
The Athlon 64 is a cut-down version of the Opteron intended for
desktop systems, and is to begin shipping in September 2003. The key
feature of both processors is that they support both 32-bit and
64-bit instructions, and can dynamically alternate 32- and 64-bit
threads.

In contrast to the 64-bit Intel Itanium, which executes 64-bit code
natively but 32-bit IA-32 code only via slow translation, the Opteron
and Athlon 64 are 64-bit processors that can execute 64-bit code
using the AMD64 instruction setcalled
"long" modeand can also
execute standard 32-bit code natively, called
"legacy" mode. To support 32- and
64-bit operations in one processor, AMD modified the Athlon XP core
to add eight 64-bit general-purpose registers and eight 64-bit
versions of the original eight 32-bit general purpose registers.
These 64-bit registers are accessible only when the processor is
operating in long mode. In legacy mode, the Opteron and Athlon 64
processors appear to 32-bit software as a standard 32-bit Athlon
processor.

The Opteron and Athlon 64 are incompatible with current chipsets and
motherboards, so using either requires buying or building a new
system. As of July 2003, Opteron systems and motherboards are in
limited distribution. We expect Athlon 64 products to become
available in September 2003.

4.5.2 Opteron

The Opteron is based on the variant of the K8 core codenamed
Sledgehammer. Various Opteron models support 1-, 2-, 4-, and 8-way
operation and are targeted at servers. AMD plans to produce at least
three Opteron series. Opteron 100-series processors support only
1-way processing, and are due in September 2003. Opteron 200-series
processors support 1- and 2-way processing, and shipped in April
2003. Opteron 400-series processors support 1-, 2-, 4-, and 8-way
processing, and are to ship in September 2003 and into 2004.

Rather than the clock speed designations or QuantiSpeed model numbers
AMD used for earlier processors, AMD assigns each Opteron model an
arbitrary number to indicate relative performance. For example, the
Opteron processor roadmap includes the 140, 240, and 840 models,
which operate at 1.4 GHz; the 1.6 GHz 142, 242, and 842 models; and
the 1.8 GHz 144, 244, and 844 models. AMD plans to release later
Opteron models operating at 2.0 GHz (presumably the 146, 246, and 846
models), as well as models operating at 2.2 GHz (148, 248, and 848).

Opteron processors use 6.4 GB/s HyperTransport Technology (HTT)
channels to provide a high-speed link between the processor
components themselves and to the outside world. The Opteron has three
HTT channels, which may be either of two types. Coherent HTT channels
link the processor to other Opteron processors. Opteron 100-series,
200-series, and 800-series processors have zero, one, or three
coherent HTT channels, respectively. Standard HTT channels link the
processor to I/O interfaces such as a Southbridge or PCI Express
bridge.

Do not confuse AMD HTT (HyperTransport Technology) with Intel HTT (Hyper-Threading Technology). You'd think they could come up with different TLAs. It isn't like there aren't lots of letters to choose from.

The
Opteron features a 1024 KB L2 cache and a dual-channel DDR333 memory
controller, which uses a 144-bit interface that requires 72-bit ECC
memory. Relocating the memory controller from the chipset, where it
has traditionally resided, directly onto the processor core allows
memory to be more tightly integrated with the processor for higher
performance. The downside is that the Opteron is limited to using
memory no faster than DDR333 unless AMD changes the processor core
itself, or unless a chipset maker adds an external memory controller.

Informed sources speculate that AMD may tweak the shipping K8 core to add support for DDR400 and perhaps DDR533. Support for DDR-II will come no earlier than mid-2004, pending JEDEC approval of a final DDR-II specification.

The Opteron uses Socket 940, newly
introduced by AMD for this processor. Relative to Socket 462, those
extra contacts are used primarily to support the three HTT channels.

4.5.3 Athlon 64

The Athlon 64 processor is based on the variant of the K8 core
codenamed Clawhammer. The Athlon 64 supports 1- and 2-way operation,
is due in September 2003, and is targeted at desktop systems. The
Athlon 64 differs from the Opteron in the following important
respects:

Rather than the three HTT channels used by the Opteron, the Athlon 64
has only one HTT channel.

Rather than the 144-bit dual-channel DDR333 ECC memory controller
used by the Opteron, the Athlon 64 has a 64-bit single-channel DDR333
non-ECC memory controller. (Shipping models may include DDR400
support.) The narrower memory interface of the Athlon 64 means its
memory bandwidth is half that of the Opteron. Like the Opteron, the
Athlon 64 integrates the memory controller onto the processor.

The Athlon 64 and Opteron both have the AMD-standard 128 KB L1 cache,
with 64 KB allocated to instructions and 64 KB to data. Opteron
processors provide 1 MB of L2 cache. Athlon 64 processors are
available with either 256 KB or 1 MB L2 cache. Our moles tell us that
for performance reasons, AMD may decide to ship the
"small" Athlon 64 with 512 KB L2
cache rather than 256 KB.

Most Opteron systems will be built around the server-class AMD
8000-series chipset. Most Athlon 64 systems will use desktop-class
chipsets such as the

n VIDIA

n Force3, the VIA K8T800/K8M800, and others.
Based on our experiences with the

n Force and

n Force2 Athlon chipsets, we expect the

n Force3 to be the best Athlon 64 chipset.

The Athlon 64 uses Socket 754, another new AMD socket. As with Socket
940, the additional contacts are necessary to support the single HTT
channel supported by the Athlon 64. Because the Athlon 64 has only
one HTT channel, it can use the smaller socket.

Table 4-6 details the important characteristics of
the Opteron and Athlon 64 processors, with the Barton-core Athlon XP
shown for comparison. Most of the items are self-explanatory, but a
couple deserve comment.

AMD regards the Athlon XP as seventh-generation and the
Opteron/Athlon 64 as eighth-generation. We consider both of those
processor families to be hybrids, straddling the generational
boundaries defined by Intel processors. In particular, the 64-bitness
of the Opteron and Athlon 64 give them a definite claim to
eighth-generation status, but architecturally they remain near
relatives of the hybrid sixth/seventh-generation Athlon XP.

With the Opteron and Athlon 64, AMD uses the Silicon-on-Insulator
(SOI) process rather than the traditional CMOS process. SOI offers
potentially huge benefits, but at a correspondingly high risk. During
the first half of 2003, AMD's problems with SOI in
getting high yields at fast clock speeds were widely reported in the
industry press. We think the most important issue for the new AMD
processors is how well and how quickly the AMD Dresden fab will be
able to master SOI production. If they succeed, they will produce
high yields of the new processors and be able to scale clock speeds
up quickly. If they fail, the Opteron and Athlon 64 will be expensive
to produce and will languish at lower clock speeds. The phrase
"bet the company" is often used in
the high technology field, but in this case we think AMD is indeed
betting the company on the success of their SOI process.

4.5.4 Intel Pentium 5?

Intel and AMD play a constant game of leapfrog. The introduction of
the Opteron/Athlon 64 almost demanded that Intel introduce a new
processor of its own. That processor is the Prescott-core Pentium,
due in the fourth quarter of 2003, which Intel may or may not call
the Pentium 5.

On balance, we think Intel will decide to name their new processor
the Pentium 5, both for marketing reasons and for technical reasons.
From a marketing standpoint, Intel would clearly like to counter the
Opteron and Athlon processors with a newly-named processor of their
own. From a technical standpoint, the improvements in architecture
and instruction set are sufficient to justify the Pentium 5 name for
the Prescott-core processor.

No matter what Intel chooses to call this processor, it is a
significant improvement on the current Northwood-core Pentium 4.
Relative to current Northwood-core processors, the Prescott-core
processors increase L1 cache size, boost L2 cache from 512 KB to 1024
KB (matching the new AMD processors), and increase pipeline depth to
enable higher core frequencies.

Just those enhancements would have made life difficult for the new
AMD processors. But a more significant enhancement lurks within
Prescott. The Prescott New Instructions (PNI) are 13 new instructions
that extend the SSE and SSE2 multimedia instruction sets used by
earlier Intel processors. In particular, three of the new PNI
instructions are worth noting. One adds support for AV
encodingas opposed to AV decoding, which was supported by
earlier Intel processorsand two improve thread control for
Hyper-Threading Technology (HTT) operations.

The new HTT thread control instructions are likely to boost
performance substantially, with less sensitivity to application mix.
In the past, the benefit of HTT depended largely on the specific
applications being run. Some applications showed major performance
improvements with HTT, most applications showed no change, and some
actually ran slower with HTT enabled. The improved HTT threading
support available with PNI means that HTT will become more generally
useful. For more information about PNI, visit http://cedar.intel.com/media/pdf/PNI_LEGAL3.pdf.

Prescott-core processors may also have a major hidden feature. We
admit that this is pure speculation on our part, but we do have some
historical evidence for our beliefs. Intel built Hyper-Threading
Technology into Northwood-core processors, where it remained hidden
until Intel chose to reveal it. We think history may repeat itself.
Intel may have embedded their Yamhill technology into Prescott as a
hidden feature.

Intel's world view is that 32-bit processors are
sufficient for desktop systems, that only datacenters require 64-bit
processors, and that 64-bit processors should operate natively in
64-bit mode rather than as 32/64-bit hybrids. But Intel always has a
Plan B, and in this case Plan B is Yamhill. Yamhill is, in effect,
Intel's version of AMD's hybrid
AMD64 architecture. Intel would prefer to drive people to its native
64-bit Itanium architecture. But if that fails and AMD64 catches on,
Intel can spring Yamhill as a nasty surprise to AMD.
Don't be surprised if that happens.

Table 4-7 shows the important characteristics of
the Prescott-core "Pentium 5", with
the Northwood-core Pentium 4 shown for comparison.

4.5.5 Our Thoughts

We won't comment in detail on server processors,
because we don't understand that market well enough.
We note, however, that IT managers are notoriously conservative in
adopting new platforms, and the perception of Intel as the
tried-and-true 64-bit solution, particularly with regard to chipsets,
probably militates against the broad acceptance of the Opteron in the
datacenter. We're sure that the Opteron will have
some "wins", but overall we think
that 32-bit Intel processors will continue to dominate PC-server
space. Those who need the additional memory addressability and other
features of 64-bit processors will probably continue using heavy
iron, at least in the short term.

On the desktop side, the picture isn't much better
for AMD. We think the Intel Pentium 5 (or whatever Intel chooses to
call it) will walk all over the Athlon 64. Although the Athlon 64
runs 32-bit code competentlysomething Intel has never been
able to achieve with its 64-bit processorsits forte is 64-bit
operations, and for now 32-bit operations are sufficient for the
desktop. The only 64-bit operating system available is Linux,
although Microsoft promises a 64-bit Windows Real Soon Now. Even if
that comes to pass, the dearth of 64-bit applications programs means
that the Athlon 64 will be operating in 32-bit mode nearly all the
time.

Considered as a 32-bit processor, the Athlon 64 is in effect a
slightly enhanced Athlon XP. It operates at a severe disadvantage
relative to the Prescott-core Pentium. AMD had severe teething pains
getting the K8 core running faster than 1.8 GHz, and we do not expect
the K8 core to scale nearly as well as the new 0.09m Intel
core. We think it likely that when the new Intel core debuts at 3.4
GHz, it will match or exceed the fastest Athlon 64 model in most
32-bit operations. And, while AMD has to work very hard for each
increment in Athlon 64 clock speed, we expect the new Intel core to
scale effortlessly to 5 GHz or faster.

Although we admire AMD and appreciate the results of their
competition with Intel, we're forced to conclude
that AMD is likely to be an also-ran in the desktop processor race
throughout 2003 and well into 2004. The arrival of 64-bit Windows and
64-bit applications may help somewhat, but we think it will be
insufficient to turn the tide. Certainly, 64-bit processing (and
memory addressability) will be a blessing for some people. Those who
work with huge databases or do serious image processing and video
work can use every bit of horsepower and memory they can get. But for
the most part we think 64-bit processing for the desktop is a
technology of the future, and is unlikely in the short term to create
a large demand for the new 64-bit AMD processors.