Speed differences between external and internal L2 cache?

[VerticalDiscussions]

Hey guys, so i was wondering if you could lend me a hand here, regarding this issue. So ive been doing a school questionary about cpu architecture and specific technologies inside of it, and i was unable to actually find anything related to this, maybe because external cache memory is extinct i guess, was the teacher who even spoke about external cache in the first place. So i was wondering if you guys can tell me if the difference between the CPU internal L2 cache and past external L2 cache speed. Does it have to do with the FSB speed on the motherboard for the external cache and the internal ones benefit from the internal clock speed? Thanks if you can help

[xentropa]

In general, the longer the wire distance, the more likely for distortion of signals due to, jitter, cross talk, radiation loss etc.  These effects can be greatly reduced if cache memory and cpu logic are all integrated within the same chip.  For external components, such as computer memory, there is a large distance between the CPU and memory elements and on top of that, the connection points (CPU / memory socket) all create problems for high speed data transfer.

 

L1-L3 cache on a CPU probably uses SRAM which has switching times of 0.5 to 1 ns or so (as of today).  It probably wouldn't make sense to use SRAM with switching speeds of that magnitude if the copper wires on the motherboard cannot sustain a signal strong and precise enough to take advantage of it.  In the past, there may have been a time where speeds were not high enough that it would really push the precision limits of the circuit wires but that is probably the case today.

[DXMember]

https://www.akkadia.org/drepper/cpumemory.pdf

 

What do you mean by External Cache though?

 

Modern Intel x86 CPUs have different memery for different purposes

the fastest memory are the registers where operation results as well as operands are stored.

the next one would be L1 cache which splits into L1d (for data) and L1i (for instructions)

the next after that would be L2 cache

Those cache levels are general purpose, there are a lot of special purpose caches for example TLB (Table-Look-Aside-Buffer, for mapping virtual memory addresses to physical memory addresses)

All of these are locaded inside the CPU and every CPU Core has it's own set of thse memory circuits on a modern multi core CPU.

the L3 cache is shared amongst the cores on the modern Intel x86 implementations, so it's still inside the CPU and is internal memory for the CPU, but it's external for Cores.

Some implementations, for example i7-5775C also has EDRAM (Embedded Dynamic Random Access Memory) that it uses either for iGPU as VRAM, or as L4 cache.

 

I believe what you are looking for should be called CPU internal memory and CPU external memory. Because having CPU external cache is pointles, it would just be too slow and the main system memory could be accessed by that point.

[VerticalDiscussions]

24 minutes ago, DXMember said:

-snip-

Okay thanks for the help