L1 Cache how does it affect our systems?

[darkarius]

Today I was looking at Newegg.com and I noticed the regular AMD Athlon64's have 64 x 64 of L1 Cache while the
Athlon64x2's had 128 x128 of L1 Cache, to top this all off I found that the Intel Core2's only have 32 x 32 of L1 Cache. So my question is what does L1 Cache do, how does it affect our system and in this area which proccesor is better?

[Fozzik]

The architectures are completely different...so it's really not something you can use to compare different processors.

Level 1 cache is the place for the instructions and data that are currently being worked on (or will be used very soon). The size a certain processor needs really depends on the overall architecture, how it moves information around, etc.

An Athlon 64 X2 is a dual-core processor... it's really just two Athlon 64's put together into a single chip. That's why it has double the level 1 cache.

The way to compare processors is to look at real-world applications and how they perform. One CPU might have less level 1 cache, less clock speed, less front-side bus speed, and still be much faster in real programs. It's just much to complex a system to break it down to individual items and compare them. There are a lot of good hardware sites which test how CPUs perform in real applications...and that information is really the only true way to compare.

[darkarius]

The architectures are completely different...so it's really not something you can use to compare different processors.

Level 1 cache is the place for the instructions and data that are currently being worked on (or will be used very soon). The size a certain processor needs really depends on the overall architecture, how it moves information around, etc.

An Athlon 64 X2 is a dual-core processor... it's really just two Athlon 64's put together into a single chip. That's why it has double the level 1 cache.

The way to compare processors is to look at real-world applications and how they perform. One CPU might have less level 1 cache, less clock speed, less front-side bus speed, and still be much faster in real programs. It's just much to complex a system to break it down to individual items and compare them. There are a lot of good hardware sites which test how CPUs perform in real applications...and that information is really the only true way to compare.

Ok I see where you are coming from, however L2 Cache seems to have a impact on all proccesors as far performance and peoples recommendations go. Is this a more signifigant setting-how does it affect things. Can you take the same approach as the L1, that it depends on the architecture of the chip or is this a more general need for any architecture?

[Fozzik]

Same as level one cache. It is possible to speculate that a larger level 2 cache may help with certain types of programs or certain types of data...but the end result is that the overall system performance is what matters. For instance... you might have a CPU with a very large level 2 cache, which means it can hold a lot more of the data and instructions the CPU needs. Being able to hold more data/instructions should make it perform better...but what if that same CPU has a rather limited memory interface and has to wait on the main memory a lot? Now that level 2 cache isn't doing you much good...and a CPU with maybe less level 2 cache, but a more balanced and faster memory bus, will outperform the one with the larger cache.

Hopefully this makes sense. If you are picking between two of the exact same processor architecture (like between two Core 2 Duo processors, one with 2MB level 2 cache and one with 4MB level 2 cache), you can probably assume that at least in some situations (moreso in the future) a larger level 2 cache is better. Is it worth the greater amount of money? That's a harder question, because in most cases level 2 cache seems to have little effect on real application performance.

Again, the best way is the real world benchmarks. Specs of any kind are very often misleading.