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what is L1 and L2 cache?

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August 8, 2008 3:35:51 PM

im looking at two proccesors, the core 2 quad Q9300 at 2.5ghz and the Q6600 at 2.4ghz. the Q9300 has 6mb of L2 cache and the Q6600 has 8mb of L2 cache. its only 2mb more but if its really important ill get the Q6600 but if its not then the smaller, faster Q9300 is what ill get. but i dont know what L2 cache is. thanks for replies

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August 8, 2008 4:02:18 PM

xxcoop42xx said:
im looking at two proccesors, the core 2 quad Q9300 at 2.5ghz and the Q6600 at 2.4ghz. the Q9300 has 6mb of L2 cache and the Q6600 has 8mb of L2 cache. its only 2mb more but if its really important ill get the Q6600 but if its not then the smaller, faster Q9300 is what ill get. but i dont know what L2 cache is. thanks for replies


Quote:
but i dont know what L2 cache is


L2 cache is the amount of data a processor is capable of storing waiting to be processed.
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August 8, 2008 4:10:13 PM

ok thanks guys for the response
August 8, 2008 8:44:26 PM

Q9300

Read the specs on Maximum PC Head to head. Q6600 has more L2 but Q9300 (even though less L2) has more speed. Speed always wins + newer architecture 45nm.
August 8, 2008 10:03:18 PM

The use of cache memory stems from the fact that your main system RAM runs much slower than the CPU core. If the CPU had to wait for the slow main RAM for every new byte of instructions or data, it would be ridiculously slow. Ideally, you would have all your main RAM on the CPU chip itself, running at the same speed as the CPU's core, but that would be ridiculously expensive.
Since RAM tends to be accessed as chunks of instructions/data from adjacent addresses rather than individual bits scattered all over the place, designers add a relatively small amount of fast RAM as a "cache" to the CPU chip. Although the first time the CPU needs data, it has to wait for the slow main RAM, when that data finally arrives, a copy is saved in the cache. If the CPU next needs data from a nearby address, there is a high chance (~90%) that the data is in the cache, which means no delay in reading it into the CPU.
The bigger the cache, the more it can hold but the more expensive it is. Normally, current CPUs have a small primary "L1" cache which runs at full CPU core speed with low latency and a secondary "L2" cache with longer (slower) latency or slower speed, or both.
L1 cache sizes are typically on the order of 8-64K, while L2 cache sizes range from around 128K to 6MB or more. Today's mainstream CPUs have at least 2MB of L2 cache.
The bottom line is that L2 cache pretty much just acts as a buffer for the slow main RAM; as long as you have "enough", more doesn't make a big difference. A few MB is about "enough" these days.
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