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What is L3 Cache?

The L3 cache has been typically integrated into the motherboard in the past, but modern CPUs models have now been incorporated with a native cache for increased performance.
A central processing unit. L3 cache is a CPU cache.
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  • Written By: R. Kayne
  • Edited By: O. Wallace
  • Last Modified Date: 22 August 2014
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Level 3 or L3 cache is specialized memory that works hand-in-hand with L1 and L2 cache to improve computer performance. L1, L2 and L3 cache are computer processing unit (CPU) caches, verses other types of caches in the system such as hard disk cache. CPU cache caters to the needs of the microprocessor by anticipating data requests so that processing instructions are provided without delay. CPU cache is faster than random access memory (RAM), and is designed to prevent bottlenecks in performance.

When a request is made of the system the CPU requires instructions for executing that request. The CPU works many times faster than system RAM, so to cut down on delays, L1 cache has bits of data at the ready that it anticipates will be needed. L1 cache is very small, which allows it to be very fast. If the instructions aren’t present in L1 cache, the CPU checks L2, a slightly larger pool of cache, with a little longer latency. With each cache miss it looks to the next level of cache. L3 cache can be far larger than L1 and L2, and even though it’s also slower, it’s still a lot faster than fetching from RAM.

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Assuming the needed instructions are found in L3 cache (a cache hit), bits of data might be evicted from L1 cache to hold the new instructions in case they’re needed again. L3 cache can then remove that line of instructions since it now resides in another cache (referred to as exclusive cache), or it might hang on to a copy (referred to as inclusive cache), depending on the design of the CPU.

For example, in November 2008 AMD® released their quad-core Shanghai chip. Each core has its own L1 and L2 caches, but the cores share a common L3 cache. L3 keeps copies of requested items in case a different core makes a subsequent request.

The architecture for multi-level cache continues to evolve. L1 cache used to be external to the CPU, built into the motherboard, but now both L1 and L2 caches are commonly incorporated into the CPU die. L3 cache has typically been built into the motherboard, but some CPU models are already incorporating L3 cache. The advantage of having on-board cache is that it’s faster, more efficient and less expensive than placing separate cache on the motherboard.

Fetching instructions from cache is faster than calling upon system RAM, and a good cache design greatly improves system performance. Cache design and strategy will be different on various motherboards and CPUs, but all else being equal, more cache is better.

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Discuss this Article

anon952595
Post 45

The writer needs to explicitly happens when "bits of data are evicted from L1 cache" Where do those bits go? I assume the L3 cache since it has gone through 1 and 2L cache. The article seems to overly simplify a couple of things, but for the most part reads well

anon951182
Post 44

Is there a system configuration report that can show me my levels of ram on my pc (running XP)?

anon290142
Post 39

Is it possible that one day ram and the cpu will come in one unit?

I briefly heard about quantum entanglement the other day. Perhaps that will come into play with speeding up data retrieval and manipulation from the ram.

elgun
Post 38

Please help me. I have an l3 cache on my motherboard (as internal hardware). Which model motherboard do I have?

anon162544
Post 34

My Phenom II x2 3.1ghz processor has 6mb of L3 cache and a TDP rating of 80w. I looked at the specs for a 3.1ghz Athlon II processor. The specs look the same, except for no L3 cache and a TDP rating of only 65w. Does this mean the L3 cache uses a power hungry 15w? Aye Caramba!

anon149631
Post 33

My PC Only has 512kb of L2 cache.

anon147839
Post 32

You know, when you define something, you're not supposed to use the word you're defining to define it.

anon138824
Post 31

wow this was the first hit and i learned something new. thank you.

Gerry
Post 30

Simply excellent

anon133227
Post 29

CPU is central processing unit. not computer processing unit. but otherwise, great info!

anon129012
Post 28

Thank you, it's what i wanted to know. Now on seeing that L3 cache cost more to get on a cpu, who would be more suited to needing L3?

anon120453
Post 26

lovely, short and crisp definition.helped me figure out what l3 meant. thank you. -- dhira

anon118470
Post 24

Nice job. I tried to find out what L3 cache was a few months ago, but couldn't find an easy explanation. This article is very easy to understand. Thanks.

anon105698
Post 22

nice nice, easy to understand and i finally know what L3 cache is. Thanks for the easy info!

anon100240
Post 21

Good article. Thank you!

anon96250
Post 19

Very good article. The author has used simple words to present a complex matter in layman's terms. Easy to understand even for a newbie like me. Well done.

anon94741
Post 18

thanks. this information is really worthy.

anon86774
Post 16

Thank you!

anon86134
Post 15

Incredibly helpful, good information to have when making decisions.

anon85174
Post 14

It's useful. Thank you.

anon84991
Post 13

great work. thanks.

anon83594
Post 11

I'm an ignorant in this PCs subject. Thanks because I am starting to learn!

anon80957
Post 10

Simple and to the point. Thank you.

anon76220
Post 9

Very easy. thanks.

anon76123
Post 8

Very helpful. Thanks.

anon73988
Post 7

very helpful writing indeed. thank you very much. Diganta

anon72636
Post 6

Very informative article. It explains the cache design very well. Little Jasmin97

anon71252
Post 5

Simple and straight-forward explanation. thanks to the author.

anon67302
Post 4

nice. it's easy to understand now.

anon67084
Post 3

It was excellent. I got what I need.

anon66274
Post 2

very good definition, thanks.

anon49806
Post 1

Excellent description of all levels of cache. Very clear, precise and understandable. Well done, helped me loads. Stuart

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