[Solved]: Can the memory cache hold instructions?

Problem Detail: 

My teacher told us that when the ram runs out of space it will push a program in the cache, i argued that the program should go to the swap space in the hard drive, plus the memory cache cannot hold instructions because instructions and data have different access patterns, it can only hold data frequently accessed. So i am asking the experts, can the memory cache hold instructions ?
Edit : what i mean by memory cache is the L1 memory cache

Asked By : Baroudi Safwen

Answered By : tillz

Not perfectly sure whether i understood your question correctly. Basically, there are multiple questions:

A) 'when the system runs out of ram [...] push to cache' A cache is a dedicated storage to accelerate the access to often-used Resources. So no, neither ne CPU-cache nor any other cache is used to replace missing ram. I really think your professor wanted to explain SWAP

B) In fact, there are different architectures for computer systems. One of them is the Harvard Architecture where two different memories exist. One is reserved for instructions, while the other is used for data. This Architecture is used by the popular AVR Microcontrollers from Atmel and other MCUs.

The other architecture is the von-Neumann-architecture (sometimes also called Princeton-architecture). This one has exactly one memory, which is used for instructions and data. This architecture is used in all Computer systems we know as 'PC' today. This architecture is by the way the reason for most of the really bad security problems (e.G. buffer overflows). In a vulnerable software, an attacker can put instructions somewhere in the memory (the sections which originally should only hold 'data' like strings), and it'll be executed by the processor if its in the 'correct' location.

To return to your question: The CPU-cache doesn't care which memory gets cached. It's simply memory. The sections which are accessed more often will be cached. In a recursive function (many branches to the same location in the one memory), the CPU cache may hold instructions.

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