Intel's Pentium M on the Desktop - A Viable Alternative?
by Anand Lal Shimpi on February 7, 2005 4:00 PM EST- Posted in
- CPUs
Final Words
As a mobile processor, the Pentium M cannot be beat - we've actually seen why, even in this comparison today. With a highly power optimized architecture, the Pentium M continues to deliver performance that is competitive with other mobile CPUs on the market. The problem is that in the transition to the desktop world, its competitors get much more powerful, while the Pentium M is forced to live within its mobile constraints.Think of it like this - the Pentium 4 and Athlon 64 are clearly the stronger chips of the three, as we have proved in today's review. However, in the mobile world, the Pentium 4 and Athlon 64 are often castrated or limited either by low clock speeds, single channel memory controllers or more physical constraints (e.g. you can get desktop P4 performance, but only in a 13lbs notebook). The Pentium M however, was designed from the ground up with these types of constraints in mind, and thus, excels quite well with them in place. Begin to remove the constraints and the Pentium M appears to be much less impressive compared to the Pentium 4 and Athlon 64 because the chip was designed to perform best with those constraints in place. The very low latency 2MB L2 cache is a prime example of this design mentality. A large L2 cache reduces the need for a high bandwidth memory bus, and making it low latency means that the CPU is even less dependent on such a bus.
The fact of the matter is that the Pentium M, while excellent as a mobile CPU, isn't the response from Intel that everyone is hoping for. The successor to the Pentium 4 won't be an architecture derived from the Pentium III, there's just no way around that. Intel has invested too much time and money into the optimization of applications for the Pentium 4 architecture and its execution core to throw it all away and revert to the old way of doing things.
That isn't to say that elements of the Pentium M design won't be included in Pentium 5 or whatever the next chip will be called. Even today's Pentium 4 already has a handful of key features borrowed from the Pentium M design. We saw examples of this with the launch of Prescott; the indirect branch predictor used in Prescott was originally introduced with the Pentium M processor. It would also be safe to say that a number of improvements that Intel is introducing in the next version of the Pentium M, the dual core Yonah, will eventually make their way into future Intel desktop CPUs as well.
But with a very high cost of ownership, thanks to high motherboard prices and correspondingly high CPU prices, not to mention a very limited upgrade path, the Pentium M just isn't suited for the desktop. And unless these deciding factors change significantly in the near future, it won't be for some time to come.
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fitten - Tuesday, February 8, 2005 - link
Also, it's interesting that there are many benchmarks chosen which are known to stress the weaknesses of the Pentium-M... not that it isn't interesting information. For example, there seems to be a whole lot of FPU intensive benchmarks (around 15 or so, all of which the Pentium-M should lose handily - known before they are even run) so kind of just hammering the point home I guess.Anyway, the Dothans held up pretty well from what I can see... Most of the time (except for the notable FPU intensive and memory bandwidth intensive benchmarks), the Dothan compares quite well with Athlon64s of the same clock speed that have the advantage of dual channel memory.
fitten - Tuesday, February 8, 2005 - link
The other interesting thing about the Athlon64 vs. Dothan comparison is that even with dual channel memory bandwidth on the Athlon64's side, the single channel memory bandwidth of the Dothan still keeps it very close in many of the benchmarks and can even beat the dual channel Athlon64s at 400MHz higher clock in some.Anyway, the Pentium-M family is a good start. Some tweaking here and there (improved FPU with better FPU performance and maybe another FPU execution unit, improved memory subsystem to make good use of dual channel) and it will be at least as good as the Athlon64s across the board.
I own three Athlon64 desktops, two AthlonXP desktops, and two Pentium-M laptops and the laptops are by no means "slow" at doing work.
KristopherKubicki - Tuesday, February 8, 2005 - link
teutonicknight: We purposely don't change our test platform too often. Even though we are using a slightly older version of Premiere, it is the same version we have used in our other processor analyses.Hope that helps,
Kristopher
kmmatney - Tuesday, February 8, 2005 - link
There's also a Celeron version that would have been intersting to review. The small L2 cache should hurt the performance, though. I think the celeron version using something like 7 Watts. It would make no sense to put a celeron-M in such an expensive motherboard, though.Slaimus - Tuesday, February 8, 2005 - link
I think this indirectly shows how AMD needs to update its caching architecture on the K8. They basically carried over the K7 caches, which is just too slow when paired with its memory controller. Instead of being as large as possible (as evidenced by the exclusive caches) at the expense of latency, the K8 needs faster caches. The memory bandwith of L2 vs system memory is only about 2 to 1 on the K8, which is to say the L2 cache is not helping the system memory much.sandorski - Monday, February 7, 2005 - link
I think the Pentium M mythos can now be laid to rest.mjz5 - Monday, February 7, 2005 - link
to #29:your 2800 is the 754 pin.
the 3000+ reviewed is the 939 pin which is 1.8. the 3000+ for the 754 is 2.0 ghz
kristof007 - Monday, February 7, 2005 - link
I don't know if anyone else noticed but the charts are a bit off. My A64 2800+ is running at a stock 1.8 ghz .. while in the review the A64 3000+ is running at 1.8 ... weird!knitecrow - Monday, February 7, 2005 - link
#251) Intel and AMD measure TDP differently... and TDP is not the same as actual power dissipation. The actual dissipation of 90nm A64 is pretty darn good.
2) A microprocessor is not made of Lego... you can't rearrange/tweak parts to make it faster. It takes a lot of time, energy and talent to make changes -- even then it may not work for the best. Prescott anyone?
Frankly I’ve been waiting for a good review of P-M's actual performance. I really don't trust those "other" sites.
k00kie - Monday, February 7, 2005 - link