17 - Memory and Cache

Question 1

What does the maximal memory size depend on?

Answer 1

The address width.

Question 2

What is the address width determined by ?

Answer 2

• The number of bits in the CPU address registers ie IP

- The number of lines in the address bus.

Question 3

What’s the maximal memory size with a 32 bit address width (x86)

Answer 3

4 Gb (2^32 = ~4 bn = 4 Gb)

Question 4

What are the slots that hold the memory cards called and how many memory chips do they hold?

Answer 4

Modules, and they hold more than a handful of them at least.

Question 5

What are the 4 levels in the memory ?

Answer 5

• Registers
• Cache memory (level 1 and 2)
• Main memory
• Mass storage

Question 6

How does the cache work and where is it placed ?

Answer 6

It’s placed between the CPU and the main memory.

When the CPU requires information from the memory it first checks the cache which contains some copied cells of the main memory.

If not found, the block of memory containing the info and some of the blocks surrounding it are moved to the cache.

Question 7

What is the ‘Localisation of Memory Access’ principle ?

Answer 7

That the next cell to be accessed usually resides close by to the one currently being accessed, so keep blocks of data as near as possible to the CPU.

Question 8

Give a memory hierarchy pyramid ?

Answer 8

CPU Registers
L1 Cache Memory
L2 Cache Memory
Main Memory
Disk Cache
Disk Storage
Tape Backup