My OS reports 3.8GB cached, much more than reported from CPU-Z

Question

This screen shot from cpu-z says my cpu cache is the following.

Now I see my cache my Task Manager saying 3.8 GB. Can someone explain how my CPU cached increase to 3.8 GB?

Voted to migrate to superuser.com. This is a basic hardware question, not a programming question. — Peter Cordes, Jan 10 '18 at 20:04

score 1 · Accepted Answer · answered Jan 10 '18 at 20:01

Task manager is showing you how much RAM is being used to cache the hard disk(s). CPU-Z is showing you how much internal cache your CPU has to cache RAM.

And within the CPU, there are again multiple levels of cache: Why is the size of L1 cache smaller than that of the L2 cache in most of the processors?.

So when executing a program stored on disk, the layers of caching between the source of the machine code (disk) and the instruction-fetch pipeline stage in your CPU are:

"L0" uop cache. (I think you have a recent Intel CPU, based on the cache sizes).
L1I cache (and the iTLB to cache page tables)
L2 cache (private per-core)
L3 cache (shared between all cores)

The above are built-in to your CPU's silicon chip

(optional) L4 eDRAM on some Broadwell/Skylake CPUs (inside the same physical package of your CPU, but on a separate silicon chip).

The above are all caching RAM.

Your OS's disk cache, using RAM instead of re-reading from disk every time.
inside your hard drive: 16 to 128MiB of DRAM to buffer transfers between the SATA link and the platter, and to cache repeated access to the same sector in case the OS's disk cache didn't filter that out already. But its main purpose is a transfer buffer.

All the same levels of cache would apply for reading a memory-mapped file (except it would be L1D cache, instead of uop cache + L1I).

WTF is up with downvoters this week? I assume it's just people downvoting answers to lame questions. I don't see any reason to downvote this answer (especially to DV this but not the other answer). But if there is something in need of improvement, please let me know so I can fix it. — Peter Cordes, Jan 10 '18 at 21:16

score 0 · Answer 2 · answered Jan 10 '18 at 18:56

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The L-1 through L-3 caches are CPU caches, separate from the RAM and the only way to increase them would be changing the actual CPU. They're much smaller than what you'd expect from a normal PC's memory. The cached memory reported in the task manager is part of your PC's RAM and managed by the OS' kernel.

answered Jan 10 '18 at 18:56

Nicolás Marzano

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thanks but why they call it cache if it is part of RAM? – thirstForKnowledge Jan 10 '18 at 19:25
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It's still a cache, though of dynamic size, located in your RAM, and managed by your OS. The L-1, L-2 and L-3 caches are managed at a hardware level and aren't dynamically allocated. – Nicolás Marzano Jan 10 '18 at 19:33
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The key point is that they cache different things. CPU caches cache RAM. Disk cache caches the disk. – Peter Cordes Jan 10 '18 at 21:09

My OS reports 3.8GB cached, much more than reported from CPU-Z

2 Answers2