Question

Question 1:
	a) Written only: Explain what a storage hierarchy is and its performance impact. b) Written and in class: Explain the concepts of temporal and spatial locality. c) Written only: Explain the operation of a simple directly mapped cache design. d) Written and in class: What is the purpose of a cache tag?

Answer 1

a) The storage or the memory hierarchy is nothing but a theory that is important and utilize by the CPU in order to manipulate the data. The CPU gets the instructions to be performed from the cache memory. The cache memory is located on the chip and is being utilized by the application faster as it is considered as the fastest type of memory. Hence, the RAM is being used as it store the data in it until the CPU requested for it. And then comes the disk memory, where all the other data are stored in the system for future use.

b) Temporal locality is basically used to refer the reuse of the data or any resources within the relatively small time duration. Temporal locality is a special type of the spatial locality when the perspective location is identical to the present location.

Whereas, the spatial locality is more like referring to the use of data relatively used within close storage locations. This is the storage location which is referenced at particular time.

c) Simple directed map Cache design:

A direct mapped cache usually has one block in each set and it is organized into the S = B sets. The mapping of the memory address into the cache blocks, imagine the main memory as mapped into the b-word blocks, just similar to the cache. Suppose an address in the block 0 of the main memory maps to the set 0 of the cache, similar ways the address in block 1 of main memory is mapped to the set 1 of cache. This way the mapping wraps around, block B of the main memory will map to the block 0 of cache. This is how it works.

d) The data stored in the cache memory are tagged in order to use it and find it whenever needed. This will easily help the CPU to get the data present in the cache memory.