L2 and L3 Cache Difference?

Question

While I understand that the computer cache is:

A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. The cache is a smaller, faster memory which stores copies of the data from the most frequently used main memory locations.

What is the difference between L2 cache and L3 cache?

Solution 1

The L3 cache is simply another layer of cache.

Typically there are now 3 layers of cache on modern CPU cores:

• L1 cache is very small and very tightly bound to the actual processing units of the CPU, it can typically fulfil data requests within 3 CPU clock ticks. L1 cache tends to be around 4-32KB depending on CPU architecture and is split between instruction and data caches.

• L2 cache is generally larger but a bit slower and is generally tied to a CPU core. Recent processors tend to have 512KB of cache per core and this cache has no distinction between instruction and data caches, it is a unified cache. I believe the response time for in-cache data is typically under 20 CPU "ticks"

• L3 cache tends to be shared by all the cores present on the CPU and is much larger and slower again, but it is still a lot faster than going to main memory. L3 cache tends to be of the order of 4-8MB these days.

Solution 2

Different processors use different types of cache.

All processors rely on L1 cache, this is usually located on the die of the processor and is very fast memory (and expensive). L2 cache is slower, bigger and cheaper than L1 cache. Older processors used L2 cache on the motherboard, nowadays it tends to be built in to the processor. L3 cache is slower, bigger and cheaper than L2 cache. Again this can be on chip or on the motherboard.

It is possible to have L4 or higher cache, but this is not proving to be worth doing.

If you need an explanation of how cache works, I'll look in to putting an article together.

i stole this from www.webopedia.com

A memory cache, sometimes called a cache store or RAM cache, is a portion of memory made of high-speed static RAM (SRAM) instead of the slower and cheaper dynamic RAM (DRAM) used for main memory. Memory caching is effective because most programs access the same data or instructions over and over. By keeping as much of this information as possible in SRAM, the computer avoids accessing the slower DRAM.

Short for Level 1 cache, a memory cache built into the microprocessor.

Short for Level 2 cache, cache memory that is external to the microprocessor. In general, L2 cache memory, also called the secondary cache, resides on a separate chip from the microprocessor chip.

As more and more processors begin to include L2 cache into their architectures, Level 3 cache is now the name for the extra cache built into motherboards between the microprocessor and the main memory.

the l2 cache is now always built onto the processor for x86 archetechure

Comments

[sawdust]

Download and run Memtest86+. It will report the size and performance (e.g. transfer capability in megabytes per second) of main memory and the caches.