what is this part of the processor and what does it do
Its the same as L2 cache, its the third place processors go to quickly store information (L1 first, L2 second...etc), and just like L2 cache the more the better. Generally they are found only in server processors.
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Several Companies have tried to implement this, but as mentioned above, it is usually found on server processors. I have seen it sometimes put on the CPU itself and sometimes on the Northbridge. It is not widly used on desktops because cache is made of SRAM, which compared to traditional ram is extreemly expensive. Personally I cant think of any advantage over a large l2 cache preformence wise, but having it on a separate die allows it to be meerly slapped onto a server CPU or motherboard without having to respin, redesign and create a separate Fab line for high-cache CPU's.
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