Pentium 4 processors provide good performance, especially with picture editing or sound when SSE instructions are used efficiently, but have a rather high thermal dissipation. This is especially true since the release of the Pentium 4 90-nm « Prescott ». So, is this the trade-off you get if you want to put together a platform based on Intel processor? No, because now there is processor for your desktop originally meant only for laptops, the Pentium M. The following is an article on this product, which will also interest laptop owners eager to know their processor’s real performance compared to other architectures.
The Pentium M architecture
Unlike the Pentium 4, which is based on NetBurst architecture, the Pentium M is actually based on P6 architecture introduced before the millineum. It’s been updated since the release of the first Pentium M, the « Banias » 130 nm.
the Dothan. Most of the processor’s 140 million transistors are used for cache L2 (on the left)First of all, the Pentium M supports SSE2 instructions, which uses SSE 128 bit registers to calculate two 64 bit floating point or whole numbers. Also, the processor operates with an increased amount of stages, so the Pentium M is able to reach higher frequencies than the Pentium III, which is stuck at 1.2 GHz. The pipeline is longer than the 10 stages of the Pentium III, but shorter than the 20 stages of the Pentium 4 130 nm or the 31 stages of the Pentium 4 90 nm.
This isn’t the only change, as Intel has also improved branch prediction mechanisms to reduce, according to the manufacturer, the number of errors by 20% compared to the Pentium III and increase performance in practice by 7%. The Pentium M is also able to fuse micro-operations to use less processor resources. According to Intel, this fusion reduces the number of processed micro-operations by 10%. The gain in practice is 5% for whole numbers and 9 % for floating point numbers calculations. Finally, the Pentium M also has a dedicated stack engine, an part of memory that temporarily stores registers when a procedure or function is called upon. This dedicated unit reduces the usual processed micro-operations by 5%.
Improvements not only involve instruction units. Cache has also been increased from 32 Kb for the Pentium III to 64 KB for the Pentium M cache L1, 32 KB for data and 32 KB for instructions. The cache L2 has been improved to 1 MB for the Pentium M 130 nm Banias and 2 MB for the Pentium M 90nm Dothan. Dothan processors also have an improved data pre-fetch and register access management compared to the 130 nm version.
Finally, Intel uses the same processor bus as the Pentium 4. This 64-bit data Quad Pumped bus functions at 100 MHz or 133 MHz for the latest Pentium Ms. Bandwidth, up to 3.2 and 4.3 GB/s, isn’t adequate to fully use the dual channel DDR memory bandwidth. This is due to the fact that the address bus is 32 bits and 4 GB of memory are addressable, and also that this bus doesn’t support the bi-processor.
The Pentium M
For the time being, 130 nm processors have almost all been replaced by 90nm ones, which are more efficient and have a lower power consumption. They dissipate up to 21 Watts instead of 24.5 for the 130 nm. There are currently 11 such processors on the market:
- Pentium M 770 : 2.13 GHz, FSB533
- Pentium M 765 : 2.10 GHz, FSB400
- Pentium M 760 : 2.00 GHz, FSB533
- Pentium M 755 : 2.00 GHz, FSB400
- Pentium M 750 : 1.86 GHz, FSB533
- Pentium M 745 : 1.80 GHz, FSB400
- Pentium M 740 : 1.73 GHz, FSB533
- Pentium M 735 : 1.70 GHz, FSB400
- Pentium M 730 : 1.60 GHz, FSB533
- Pentium M 725 : 1.60 GHz, FSB400
- Pentium M 715 : 1.50 GHz, FSB400
