L2 Cache

Hey, I was just wondering how much of an impact on performance the L2 Cache of a processor has. What tends to be a reasonable amount to look for in a laptop and will the difference between a 512kb and a 2MB cache be completley evident in everyday use?

Secondly, does the processor bus greatly impact performance and would this be more important over the L2 cache? My desktop at the moment has 246kb of L2 and a bus speed of 167.6Mhz yet performs far faster than my laptop which has 1024kb of L2 and a bus speed of 99.8Mhz. Is there any reason for this or could the difference be due to other factors such as memory or type of processor?

 

It could be due to any of two dozen factors.

Also, cache size in particular does not have a linear effect on performance.

Going from, say, 128KB cache to 256 yields a bigger performance boost than going from 256 to 512. And going from 256 to 512 probably yields a bigger boost than going from 512 to 8192.
On the other hand, on pretty much any modern system, bus speed doesn't matter that much. It's fast enough to serve most memory requests without too much trouble.

Basically, no matter which CPU you buy, your system will end up "fast enough". A CPU with 2MB cache might be 10% slower (at most) than a 4MB one. And a bus speed of 667 Mhz might be 5% faster than 533MHz.... Neither is going to really make a noticeable difference.

 

Ok thanks. So would a laptop with 512kb of cache still be able to handle most of the basic requirements thrown at?

 

Which processors are you looking at? AMD processors do not have as much L2 cache as Intels do because A) there is not that much room on the CPU chip itself (AMD processors have an on-board memory controller unlike Intels), and B) the memory controller as I mentioned is located directly on-chip and memory access is more convenient, so the AMD CPU does not need to store as much in L2.

512k is plenty for an AMD. As far as I know there is little difference between a 512k and 1MB L2 in their modern processors.

 

I was looking at the AMD Turion 64 x 2 TL-50 which has 512kb of L2. How would this compare with an Intel Core 2 Duo and is a certain type of processor more power efficient?

 

The Core 2 Duo is both noticeably faster than the X2 and provides better performance-per-watt. On the other hand, they tend to be far, far more expensive. That's a decision in which, like with most decisions, you have to base the performance you want versus the amount of money you're willing to spend.

 

Really, I'd be looking for the processor that is the most power-friendly so would the Core 2 Duo be the best choice?

 

CPU wise, the Core2 definitely uses a bit less power than the Turion.
But, if you're after max battery life, then it would depend more on the rest of your system. You might be comparing a Core2Duo machine with a power hogging GPU against a Turion X2 designed for mobility.

 

I'd most likely be going for Intel GMA950 graphics simply because I won't be using the laptop for 3D gaming and I want as good battery life as possible for a Core 2 Duo. Core 2 Duo in this case then?

 

There are still other factors. Namely, the capacity of the battery? What size is it? 6, 8, 9, or 12 cells? What's it mAh rating? A Turion64 X2 with a 12-cell, 8800 mAh battery will last much longer than a C2D with a 6-cell, 4000mAh battery.

 

Both are definitely fast *enough* for all everyday purposes. (Up to and including high-end gaming)