IBM ThinkPad X31 Review - Specifications
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This X31, the 2632-CBU model, has the following specifications:
- Processor: Intel Pentium M 1.4 Ghz processor
- Memory: 256 MB PC2100 RAM
- Hard Disk: 40 GB drive
- Graphics: Ati Mobility Radeon 7000 (AGP 4X) with 16 MB RAM
- Screen: 12.1” XGA TFT LCD display capable of 1024x768x32 bit color
- Audio: Integrated SoundMax chip and speaker
- Modem: Integrated 56K V.90 modem
- Ethernet: Integrated Intel PRO/100 10/100 Ethernet controller
- Wireless: Integrated Intel PRO/2100 802.11b Wireless controller
- Weight: 3.6 lbs
- Battery Life: Max rated life 5.5 hours
- Ports: 2 USB 2.0 ports, IEEE 1394 (FireWire), 1 PC Card, 1 Serial, 1 Parallel, and external display, Infrared
Keep in mind that the Pentium M is not the Mobile Pentium 4-M chip. The Pentium M chip is based on Intel's Banias core, which was revised to the Dothan core. Mobile Pentium 4-M processors are based on the Northwood core, the core whose most famous overclocker was the Pentium 4 2.4C. The primary difference between the Pentium M and the Pentium 4-M besides the core is hyperthreading support, which Banias does not have.
Going back to the Banias core, the Pentium M in this X31, being based off of Intel's .13 micrometer process, ended up being a large chip because of its 1 MB of cache. This added up to 77 million transistors, compared to the desktop Pentium 4 Northwood's 55 million. While some of you would begin to wonder about the power use, the Banias core is very good in this regard.
One reason for this is due to the Banias design. Instead of following Intel's usual "MHz Rules All" creed, the Israeli design team instead went back to the P6 core. P6 was the codename of the first Pentium Pro core before it came out. This was the first superscalar, out of order (OoO) execution core in the x86 world, and one of the first to be found anywhere. It was so good that it continued all the way to the Pentium III relatively intact, with only some minor tweaking done to add cache and increase its ability to scale in clock speed. Using that P6 design as the basis, they updated it with some parts found in the "Netburst" design that is at the core of the Pentium 4. The reason for not just starting off with the Netburst architecture is that its simply not efficient in terms of power or layout. However, it did have some very useful things in it that would be able to add performance to Banias.
One of those parts taken from the Pentium 4 is the branch predictor. Since the Netburst design can't afford the associated branches due to its extremely long pipeline and the associated latency that comes with flushing it, Intel did a lot of work to make sure that the penalty of flushing the pipe happens as little as possible. On top of the branch predictor, the Pentium M design team added to it a feature to make it even more efficient, specifically on "indirect" branches. These are hard to predict in general, as you don't know at compile time where the branch is going to go. By adding an extra buffer that keeps track of certain indirect branches' favourite "targets", the Pentium M is able to correctly guess those harder branches more often. How does this help? By wasting fewer cycles executing code it's going to throw away, then emptying the pipeline, the Pentium M conserves its energy for work that is actually useful.
Don't fall for the MHz Myth that happens to Intel fans and those who view clock speeds as the only method of indicating a processor's performance. Pentium M processors at 1.4 GHz are as fast or faster than Pentium 4-M 2.4 GHz counterparts, and can give regular Pentium 4 chips a run for their money. This gives the Pentium M an advantage because it can use less power and run faster. If you are in the market for a laptop to hold on to for a few years, you should heavily consider a Pentium M based solution.
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