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Laptop Buying Guide Part 2: CPU Codename Overload – How To Choose A Laptop Processor

Latest: Click here to read the CES 2008 laptop and UMPC news

The main processor is what makes a computer tick. Choosing the right processor (aka CPU) in a laptop is a minefield these days, mainly because names like T2310 or TL-56 don’t tell us anything about speed. For example is a T2310 actually a better buy than a T2300? So as part two of this laptop buying guide, here is the geek-speek translation of what the confusing names mean. (Click here for part one.)

In years gone by, the only spec which counted was the brute speed of a processor (or CPU – Central Processing Unit). This was measured in Hertz and it was simply a case of figuring out whether you could afford a 3 Giga-Hertz or only a 2.5 GHz chip.

One factor changed that: Power consumption. In the world of laptops this impacts all important battery life. As processors became faster they required more power which ate battery life. Intel pioneered laptop energy saving features such as SpeedStep, which reduced processor speed when less horsepower was requied. However as memory prices fell another option became available to chip manufacturers, which was to increase the processor’s on-board memory, otherwise known as the L1 and L2 Caches.

By increasing the L2 Cache in particular, the amount of RAM fetches decreases and so overall system performance goes up. This is because accessing the L2 Cache is quicker than accessing RAM. Since memory uses little power we get increased battery life and good performance by increasing the L2 Cache compared to incresing brute processor speed. Better still, two slow-ish processors (or cores) can be combined on one silicon die to increase performance whilst preserving battery power. See part one of this laptop buying guide for more info about making RAM and Cache decisions.

Why is this important? Because when you go laptop shopping, you now know that processor performance is dependent on both speed and the L2 Cache size. So with this in mind let’s talk about some of the processors on the market currently.

Intel’s premium laptop processor range is called Centrino. The Centrino brand pioneered the use of larger L2 Caches in laptops. At the budget end is the Celeron M range and sitting in the middle is Pentium Dual Core.

AMD also has three ranges. The budget range is called Mobile Sempron, in the middle is the Athlon Athlon 64 X2 Dual-Core and the top end is the briefly-named Athlon Turion 64 X2 Dual-Core Mobile Technology.

AMD follows a straightforward range structure:

Budget: Mobile Sempron has one core and a small 512KB L2 Cache. It has a four digit numeric identifier, such as 3400+.

Midrange: Athlon Athlon 64 X2 Dual Core has two cores and a small 512KB L2 Cache. It is identified by the TK prefix, such as TK-57.

High end: Athlon Turion 64 X2 Dual Core Mobile Technology processors have two cores and a 1MB L2 Cache. They go by the TL prefix, such as TL-66.

So making a choice in the AMD range is fairly straightforward as long you understand the three processor groupings. Mobile Semprons are for basic needs and are actually getting harder to find in stores. The TKs are incresingly common in low to mid range offerings and fine for general computing needs. The TLs in the AMD range have more horsepower for really taking advantage of Vista.

The Intel range on the other hand is more complex partly because it has repositioned the Pentium brand, which used to be the premium offering, at the middle of the range. Here’s how it works:

Budget: Celeron Ms have one core and predominantly 1MB of L2 Cache. They are denoted by numeric identifiers, such as 530. Celerons tend to ship with Vista Basic.

Midrange: Pentium Dual Cores have two cores and a 1MB L2 Cache. They are denoted by a T followed by four numbers, such as T2310. Pentium Dual Cores tend to ship with Vista Premium.

High end: Centrinos and Centrino Duos have either one or two cores. The Core Solo and Core 2 Solo models have one core and the Core Duo and Core 2 Duo models have two cores. The processors in the Centrino Duo range have either a 2MB or whopping 4MB L2 Cache. They are denoted with a T, U or L followed by four numbers, such as T2300. I run Vista Premium on a T2050 Core Duo 1.6 GHz with 2MB of L2 Cache and it flies along in general use.

Where it gets confusing is that Pentium Dual Core identifiers appear to cross over with the Centrino Duo range and in some cases slower Pentium Dual Core processors appear at first glance to be higher in the Intel hierarchy than similarly named Centrino Duos.

For example it may be a fair assumption to think that a T2310 is higher in the range than a T2300. The T2300 is a Centrino Duo with dual 1.66 GHz cores and 2MB of L2 Cache. However the T2310 is actually a Pentium Dual Core with slower dual 1.46 GHz cores and only 1MB of L2 Cache. Caveat emptor.

Typically for performance vs. battery life Intel is leading the way in he laptop market. In fact the original Centrino brand, which was Intel’s first foray into significantly increasing the L2 Cache on laptop processors, was so successful that they have recently revived it to be an umbrella brand for their Core ranges.

Interestingly Apple ships its MacBooks with extremely high end Centrino Duo processors. So whilst there seems to be a popular perception that Vista runs slower than Mac OSX, most Vista laptops on the market have massively slower hardware than Apple’s offerings.

That’s the geek-speek tanslation for laptop processors and the end of this two part laptop buying guide. Happy shopping!

Click here to read part one of the laptop buying guide

Latest: Click here to read the CES 2008 laptop and UMPC news

Neil Berman

http://www.neilberman.com/

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Dec 23, 2007 - Posted by | Uncategorized | , , , , , , , , , ,

2 Comments »

  1. Very useful explanation and very timely with the sales just starting over here. But what about the actual processor speed? Should one go for a 1.8GHz with 1MB of L2 rather than a 1.6GHz with 2MB of L2?

    Comment by David | Dec 27, 2007 | Reply

  2. Hi Dave,

    That’s a good question…the answer depends on usage patterns. Faster outright clock speed will be of benefit when doing intensive number crunching, whereas the extra cache comes good when files need to be constantly accessed or can be buffered (i.e. read ahead and stored in memory for processing).

    Test results I’ve seen for a desktop Core 2 Duo show that at the same clock speed, doubling the cache brings approximately 10% performance gain in some applications and 0% in others. If this holds true in your example then a 1.6GHz processor with 2MB L2 cache should in some cases approach the performance of a 1.8GHz with 1MB L2 cache.

    However, you might experience better battery runtime from the 1.6GHz laptop all things being equal as running with a larger cache uses less energy than running a faster processor.

    For light home usage such as web surfing, MP3 playback and word processing you are probably unlikely to notice a massive difference between a 1.6GHz or 1.8GHz processor. For example I perceive no notable performance difference between surfing on my 1.6GHz Core Duo Vista macine or my 2.0GHz MacBook. But I know that the extra horsepower of the MacBook’s processor makes it better suited to music recording which involves serious number crunching.

    So if I had a light usage pattern I would actually favour the 1.6GHz with the larger cache as it may well offer better battery performance. This was the precise reason I chose my Core Duo laptop over a similar machine from the same brand with a Pentium Dual Core running at a higher clock speed. However you should check the battery specs and manufacturer’s quoted battery runtime before buying.

    The test results I mentioned earlier are at: http://www.tomshardware.com/2007/10/24/does_cache_size_matter/page5.html#application_benchmarks

    Neil Berman

    Comment by Neil Berman | Dec 28, 2007 | Reply


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