2. Memory

Question 1

What is Read only memory? (ROM)

Answer 1

ROM is memory whose contents are not lost if power is lost. This is also called non-voltatile memory.

There are variations on this basic idea.

Question 2

What is Programmable ROM?

Answer 2

Programmable ROM is ROM that is programmed after manufacture. Once programmed, the basic ROM and PROM cannot be changed.

Question 3

What is Erasable Programmable ROM (EPROM) ?

Answer 3

Erasable Programmable ROM is rom where the physical links that are altered to store programs/data can be reset by exposing them to Ultraviolet (UV) radion for a few minutes.

Once done, the EPROM can be reprogrammed.

Question 4

What is Electrically Erasable and Programmable ROM (EEPROM) ?

Answer 4

Electrically Erasable and Programmable ROM is ROM that doesn’t need UV to overwrite what is already stored; it can be done electrically.

The main advantage of this is that the EEPROM does not have to be taken out of the computer to reprogram it.

Question 5

What is Random Access Memory (RAM) ?

Answer 5

RAM is a type of memory used to temporarily store instructions and data that is currently being used. It is voltile so if power is lost, so is the contents of memory.

Question 6

What are the 3 basic types of RAM?

Answer 6

Dynamic RAM (DRAM)
Static RAM (SRAM)
Non-volatile RAM (NVRAM)

Question 7

What is Dynamic RAM (DRAM) ?

Answer 7

Dynamic RAM is a type of RAM where the charged stated of a capacitor determines whether a 0 or 1 is stored. (0 = discharged, 1 = charged).

The capacitors will lost charge with time so they consatntly need to be refreshed to keep their contents.

Question 8

What is Static RAM (SRAM) ?

Answer 8

Static RAM is a type of RAM where each bit is represented by a flip-flop. The cell’s output is maintained until it is either altered to a new value or the power is lost.

Question 9

What are the disadvantages of Static RAM (SRAM) when compared to Dynamic RAM (DRAM) ?

Answer 9

More complex.
More expensive.

Question 10

What is Non-volatile RAM (NVRAM) ?

Answer 10

Non-voltatile RAM (NVRAM) is a type of RAM that is non-voltatile. A variety of different technologies are used to implement NVRAM.

NVRAM can be found in many applications such as digital cameras and MP3 players.

Question 11

Give some examples of RAM.

Answer 11

EDO RAM (Extended Data Output RAM): Used in both main memory and video cards.

SDRAM (Synchronous DRAM): the processor and the memory are in step with each other. This elimated some of the operations needed to communicate between the two devices.

DDR (Double Data Rate) SDRAM: Similar to SDRAM but theoretically could transmit data on the rise and fall of the clock. In practice, this is unlikely to occur.

Question 12

What is Cache?

Answer 12

Cache is a fasyer type of memory that is found in main memory. In other words, it takes less time to access something in cache than in main memory.

It ‘sits’ between the external memory (main memory) and the processor.

Question 13

What is a register?

Answer 13

In it’s simplist form, a register is a memory location within the processor.

Question 14

What is Virtual Memory?

Answer 14

Virtual memory is a portion of the hard disk / secondary storage that is used like RAM when the main memory / RAM is full.

Virtual memory is useful when the programs and data in use are bigger than main memory’s capacity.

Question 15

Give a rule of thumb when it comes to memory hierarchies.

Answer 15

The faster the memory, the highter the cost, making it very expensive to make all memory out of the fastest memory devices.

Slower technologies are less expensive, making it more practical to make larger memories out of these devices.

Question 16

What is the order of the memory hierarchy (fastest to slowest) ?

Answer 16

Registers, Cache, RAM, Virtual Memory.

Question 17

What is Level 1 cache?

Answer 17

Level 1 cache is built into the actual processor core. It is a piece of RAM, typically 8, 16, 20, 32, 64 or 128Kbytes, which operates at the same clock frequency as the rest of the CPU. (You could say the L1 cache is part of the processor)

Question 18

What does Level 1 cache store?

Answer 18

Level 1 cache stores instructions going to the processor. It is often split into L1 cache for instructions and L1 cache for data.

Question 19

What is a cache called that is common for both data and instructions?

Answer 19

Unified cache.

Question 20

What is Level 2 Cache?

Answer 20

Level 2 cache is used to buffer data between L1 cache and main memory. It is a unified cache.

It is normally much bigger (such as 256, 512 or 1024 Kbytes)

Question 21

What is the purpose of Level 2 Cache?

Answer 21

The purpose of the Level 2 Cache is to constantly read in slightly larger quantities of data from RAM, so that these are available to the Level 1 Cache.

Question 22

What is the principle of locality?

Answer 22

It is the idea that the data / instructions used more often should be closer to the CPU.

Question 23

What is a cache hit?

Answer 23

A cache hit is where data / instructions are required and it is found in cache.

Question 24

What is a cache miss?

Answer 24

A cache miss is where data / instructions are required and is NOT found in cache.

Question 25

What is special about the Harvard Architecture?

Answer 25

Instructions and data occupy different address spaces.

Instruction and data have seperate hardware pathways (buses) to the CPU.