Chapter 11: Hardware

Question 1

Explain the fetch-decode-execute cycle?

Answer 1

Firstly, the program instructions are copied from a storage device such as a hard disk drive or DVD to the random access memory.
FETCH
The instructions and data are moved from the RAM to the CPU
DECODE AND EXECUTE
The control unit interprets the instructions and decides what action to perform based on the opcode. During the execute phase, these instructions are carried out

Question 2

What is the difference between hardware and software?

Answer 2

Hardware are all the physical components making up the software. Software are the programs that a computer system needs to function.

Question 3

What is an embedded system?

Answer 3

A specialised computer system built within a larger device.

Question 4

What is the CPU?

Answer 4

The Central Processing Unit processes data. The way the CPU executes the program instructions is called ‘von Neumann architecture’. This was when he built a new computer that stored the program and data in the memory.

Question 5

Why do computers have RAM?

Answer 5

It can take a long time for computers to fetch data and program instructions from the hard drive. So they are stored in the RAM (a temporary store of data) so that the CPU can retrieve the information quickly.

Question 6

What is RAM and how does it speed up memory retrieval?

Answer 6

It is called Random Access Memory because each memory location can be accessed in any order. This speeds up data retrieval as the CPU can go to any location instead of having to start at the first location (serial access).
RAM is said to be volatile because if there is no electrical power then the RAM will lose all of its data.

Question 7

What are the 2 types of RAM and what are there advantages/ disadvantages?

Answer 7

Dynamic Ram (DRAM) and Static Ram (SRAM).
DRAM is slower than SRAM but it is cheaper.

Question 8

What is ROM and BIOS?

Answer 8

Read Only Memory is an integrated circuit on a chip. The data can be read but cannot be changed (data is not turned lost when power is removed). The BIOS is stored in ROM. The BIOS controls what happens to the computer when it is first switched on. It checks the hardware to ensure there are no errors and then loads basic software. Then it locates and passes control to the operating system.

Question 9

What are buses?

Answer 9

A collection of wires that carry signals or communications between components in a computer system. The control bus connects the control unit to the CPU and devices in the computer system. The CU uses it to send instructions to the components. Then the components use it to send the information back to the CPU.

Question 10

What are registers?

Answer 10

Storage locations inside the CPU. They can be accessed more quickly than RAM.

Question 11

What are some examples of registers?

Answer 11

The accumulator (A/ACC)
The program counter (PC)
The memory address register (MAR)
The instruction register (IR)
The memory data register (MDR)
The memory buffer register (MBR)

Question 12

What is the ALU?

Answer 12

The arithmetic and logic unit performs arithmetic and logical operations. Such as : addition and subtraction, multiplication and division, logical tests using logic gates, comparisons, such as whether one number is greater than another.

Question 13

What is the control unit and what are it’s two main components?

Answer 13

The CU coordinates the actions of the computer by sending out electrical control signals to the CPU.

Clock and decoder

Question 14

What is the clock?

Answer 14

A vibrating quartz crystal sends pulses to components in order to coordinate their activities. One instruction can be carried out with each pulse of the clock, therefore, the higher the clock speed, the faster the CPU can carry out program instructions.

Question 15

What is the decoder?

Answer 15

Decodes program instructions that have been brought by the memory and decides what actions should be taken. It then sends control signals to the other components to carry them out.

Question 16

What is pipelining?

Answer 16

A technique which allows modern processors to process more than one instruction at a time.

Whilst the first instruction is being decoded, the second instruction can be fetched. While the first instruction is executed, the second instruction is being decoded, the third instruction can be fetched ….. Speeding up the execution of the program.

Question 17

How do you increase microprocessor performance?

Answer 17

CLOCK SPEED
MULTI-CORE PROCESSORS
CACHE MEMORY

Question 18

What are the limitations to increasing clock speed?

Answer 18

The microprocessor generates a lot of heat, and as there are limits to the rate of cooling the microprocessor can malfunction or melt.

The instructions are processed by transistors. The rate at which they work has not become faster.

Microprocessors with clock speeds of 9 GHz require cooling by liquid nitrogen

Question 19

What is a multi-core processor?

Answer 19

A multi-core processor has more than one CPU.

2-core - dual core
4-core - Quad core

The cores can work together on the same program (parallel processing) or different programs at the same time (multitasking).

However, not all programs will run at double speed or the task might not be carried out in parallel. They might be sequential so that one task requires output from a previous task and so the second task cannot start until the first has finished.

Question 20

What is cache memory and why do we have it? Discuss

Answer 20

Bottlenecks occur when one component cannot work as fast as the others (usually RAM).

The solution to this bottleneck is to use faster memory closer to the CPU called a cache (to speed up the CPU). The cache (SRAM) is used to store recently used data and data likely to be frequently used.

The larger the cache memory, the slower it is to access the instructions and data. So, there are different levels of cache memory.
Level 1 - the fastest cache which is the smallest and closest to the CPU
Level 2 - slower than level 1 but faster than the main memory. It is checked after level 1 cache.

Cache sizes can be found in the BIOS setup screen of a computer.

Question 21

What is Virtual memory and what are adv/dis-adv?

Answer 21

When the RAM becomes full the operating system will use virtual memory to store some of the data, usually on a hard disk drive to increase total storage.

It effectively swaps needed data with data on the RAM which isn’t used very often.

DISADV:
The read/write of a hard drive is a lot slower than RAM.

If the system becomes dependant on virtual memory then the performance will drop

Often the operating system constantly swaps information between the RAM and the HD. You can hear the disk drive operating continuously. This is called ‘disk thrashing’ and slows down the execution of programs

Question 22

What is the point of secondary storage devices and what are the 3 types of storage?

Answer 22

RAM is volatile meaning data must be stored on other devices so that the data is not lost when the computer turns off.

Magnetically, Optically, Electrically