Is Cache Size Really The Key To Boosting Performance?

What Is The Impact Of Cache Size?

The first processor that came with L2 cache (though it was not integrated) was the Pentium Pro in 1995. It had either 256 kB or 512 kB second-level cache on the die and thus had a significant performance advantage over the regular Pentium processors whose cache memory was located on the motherboard. With the introduction of the Pentium II on the Slot 1 module, dedicated cache memory was planted onto the processor. However, it wasn’t before the second-generation Pentium III for socket 370 when cache memory could be found on the actual processor die. This hasn’t changed to date for performance reasons, but there still are some processors with little cache and those with a lot. So is it worth spending money for more cache? In the past, extra cache really did not make much difference in performance.

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Although there have always been measurable differences between processors with little cache and those with a lot of cache memory, it was smarter to choose devices with smaller cache to save money. But no processor model prior to Core 2 Duo was available in three different cache flavours.

The Pentium 4 carried 256 kB L2 cache in its first generation (Willamette, 180 nm) and 512 kB in the most successful, second-generation (Northwood, 130 nm). At this time, low-cost Celerons with less cache memory were produced using the same processing cores. The Celerons represented the first generation of high-end and low-cost products with the same technical origin, differing only in useable cache size and FSB/core clock speed. Feature differences were added later to further distinguish market segments.

With the introduction of the 90-nm Prescott core, 1-MB caches were introduced, and they represented the backbone of Intel’s desktop processor portfolio until the 2-MB cache, 65-nm Cedar Mill core took over. Intel even used two of these to create the second-generation Pentium D 900 series. However, the faster clock speeds and cache sizes did not mean a whole lot, even then. Now, things have changed; the Core 2 Duo’s (Conroe, 65 nm) better performance and lower power consumption have a lot to do with cache size.

AMD has been prudent about when and how to boost cache size. Presumably, this is because silicon real estate is extremely important when 65-nm output cannot satisfy the market demand and there still is a noticeable dependence on the economically less beneficial 90-nm process. Intel, on the other hand, has the advantage of producing all mainstream processors in 65-nm, and it seeks further increases in L2 cache capacity. The next Core 2 generation based on the 45-nm Penryn core will even carry up to 6 MB of L2 cache. Is this just marketing bluff or does the swelling of L2 cache capacities indeed lead to better performance? Let’s find out.

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  • nick001
    If possible, I'd like to see comparisons between the AMD and Intel CPU's with the cache disabled. Would the performance loss on the AMD processors be less as they have 512Kb/1Mb in comparison the Intel's 1/2/4Mb and due to the integrated memory controller?
    Or is the Core2Duo's architecture so much more superior that it will still beat the "more elegant solution"?
  • Geffen
    Is the question not whether cache is benfical but whether it is good use of the silicon real estate. When the Athlon upgraded from the Thunderbird core to the Palomino core with no increae is cache size it got about 5% faster for a minor increase in the transitor count (37 million to 37.2). When they upgraded from Thoroughbred to Barton which double the cache from 256kb to 512kb resulted in a huge transitor count increase from 37.6 to 54 million for a 5% speed increase. Based on this it seems to me that adding cache is a lazy but expensive way to increase performance by the chip manfactures and it would be better if they spent more time looking at other ways to improve their chips.
  • Allubz
    Just a bit of a shame you didn't add to the conclusion that the PRICE difference between the processors compared to the PERFORMANCE difference between them.
    Short: Price-performance

    Because PP-wise:
    E2160 $72.00
    E4400 $129.99
    X6800 $985.00
    Prices from Newegg (in most countries the differences are even bigger)

    So the av. difference at the same clock speed between the E2160 and the X6800 is about 10% and the price difference is nearly a horrible 1400%!!

    Like most reviews IF you add anything like this, the conclusion will probably be:

    If you've got a budget then consider taking the cheapest E2100 serie. If you want to build your-average PC take a E4000 serie and well, if you've got a wallet you found to empty then hit it with a grand to get rid of it before the cops find out.

    Anyway, my point is that I think Toms should inform people about reasonable price performance differences. If more review sites do this then manufacturers will ofcourse keep higher prices, but will see a drop in buys of these products and see their mid-range products being bought and used very well. (or they'll start producing low -and mid-range products that are very limited so they can't compete at any rate with the high-end parts).

    Just my two cents...
  • jamesalexw
    Actually the first processor to have on-die full speed 256kb L2 cache was the AMD K6-III, not the Intel Pentium III Coppermine.

    The K6-III was released in Febuary 1999, Coppermine Pentium III's didn't appear until late October.