17 Memory(NOT ASSESSED)

Question 1

HighRisc microprocessor – Harvard architecture

Answer 1

Question 2

The performance of a computer depends on aspects such as:

Answer 2

• Instruction Set Architecture
• RISC/CISC
• Clock frequency
• Memory technology
• Memory level

Question 3

Memory hierarchy and technology?

Answer 3

Question 4

ROM

Answer 4

BIOS • non-volatile • fast access • made of transistors

Question 5

SRAM

Answer 5

needs power to retain the data • typically made of CMOS transistors • accessed very quickly • volatile

Question 6

DRAM (DDR2, DDR3, DDR4)

Answer 6

made of capacitor • needs periodic capacitor charge • slow access compared to SRAM • volatile

Question 7

Non-volatile

Answer 7

magnetic, optical disks (slow access) • flash memory, fast access • reprogrammed multiple times

Question 8

Location of ROM,SRAM DRAM NonVolitile

Answer 8

Question 9

Memory sizes for different types?

Answer 9

Question 10

Retrieving data with the memory hierarchy

Answer 10

Question 11

Memory system performance metrics

Answer 11

hit: the requested data resides in a given level of memory
miss: the requested data is not located in a given level of memory

hit rate: the percentage of memory accesses found in a given level of memory

hit miss: the percentage of memory accesses not found in a given level of memory

Question 12

Equation for miss rate and hit rate?

Answer 12

Question 13

We want to know the performance of the cache memory. The CPU has accessed memory 10,000 times searching for data. A total of 1500 times the requested data was found in the main memory, and 8500 times the data was found in the cache. What are the hit and miss rates?

Answer 13

Question 14

The principle of loacality?

Answer 14

Processors tend to access memory in a very patterned way. For example, in a program running, when the PC fetches instruction at memory address X, there is a high probability that the data from memory location X+1 will be needed soon.

Question 15

There are two forms of locality

Answer 15

• Temporal locality: recently accessed items will tend to accessed again soon.
• Spatial locality: if an item is accessed, then items in nearby memory locations will tend to be accessed soon

Question 16

Why do we use the principle of locality?

Answer 16

This principle allows a computer to use small and fast memory that effectively handles information, to achive low miss rate.

Question 17

Cache Memory?

Answer 17

A cache memory holds commonly used data.

If the processor needs data, first the cache memory is checked, if the cache hits, then the data is available immediately. Otherwise, the processor check the main memory and places the data in the cache for future use.

Question 18

Tasks of the Cache memory?

Answer 18

Question 19

How is the Cache mapped?

Answer 19

• The cache memory is organised in sets (s), block (b) and ways (w).
• In direct mapped cache, an address in the main memory is mapped to a unique location (block and set) in the cache.
• In direct mapped cache, each set contains one block only

Question 20

Cache diagram?

Answer 20

Question 21

Direct mapped cache positioning?

Answer 21

Question 22

If the processor needs some data then:

Answer 22

Checks the set bits from the address, e.g., 011

2. Checks if the tag in cache matches address tag
3. Checks if valid bit is 1
4. If everything matches, then the cache hits and the data is sent to the processor

Otherwise,

1. the cache misses
2. The data is fetched from the main memory