the CPU

Question 1

What is the CPU?

Answer 1

The CPU is the central processing unit. It processes all of the data and instructions that make the system work. It is made up of three main parts- the control unit, the arithmetic logic unit and the cache.

Question 2

What is the control unit and what is its function?(CU)

Answer 2

The control unit is in overall control of the CPU. Its main job is to execute program instructions by following the fetch-decode-execute cycle.
It controls the flow of data inside the CPU to outside the CPU.

Question 3

What is the arithmetic logic unit and whats is its function?(ALU)

Answer 3

The ALU does all the calculations. It completes simple addition and subtraction, compares the size of numbers and can do multiplications and divisions.
It performs logic operations and binary shifts.
It contains the accumulator register.

Question 4

What is the Cache and what is its function?

Answer 4

The cache is very fast memory in the CPU. It slower than the registers but faster than RAM.
It stores regularly used data so that the CPU can access it quickly the next time its needed. When the CPU requests data, it checks the cache first to see if the data is there. If not it will fetch it from the RAM.

Question 5

Do caches have a lower or higher capacity than RAM and secondary storage?

Answer 5

Has very low capacity

Question 6

Are caches expensive compared to RAM and secondary storage?

Answer 6

They are expensive

Question 7

What are the different levels of cache memory?

Answer 7

L1, L2 and L3

Question 8

What are the features of L1?

Answer 8

It is the quickest but has the lowest capacity.

Question 9

What are the features of L2?

Answer 9

L2 is slower than L1 but can hold more.

Question 10

What are the features of L3?

Answer 10

L3 is the slowest out of L1 and L2 but can hold the most.

Question 11

What is a register?

Answer 11

A register is a temporary data store in the CPU. They are super quick to read/write to, quicker than any other form of memory.

Question 12

What are examples of registers?

Answer 12

Program counter, MAR, MDR and accumulator.

Question 13

What is the Von Neumann architecture?

Answer 13

It describes a system where the CPU runs programs stored in memory.

Question 14

What are programs?

Answer 14

Programs consist of instructions and data which are stored in memory addresses.

Question 15

What is a feature of the Von Neumann architecture?

Answer 15

It only uses one memory for both the data and the instructions.

Question 16

What is the program counter?

Answer 16

The program counter(PC) holds the memory address of the instruction for each cycle.

Question 17

What is the accumulator?

Answer 17

The accumulator stores intermediate results of the calculations in the ALU.

Question 18

What is MAR?

Answer 18

The memory address register(MAR) holds any memory address about to be used by the CPU. The address might point to data or a CPU instruction.

Question 19

What is MDR?

Answer 19

The memory data register(MDR) holds the actual data or instruction. This may have been fetched from memory or be waiting to be written to memory.

Question 20

What does the memory hold?

Answer 20

The memory holds the program instructions and the program data.

Question 21

How does the CPU actually work, what cycle does it follow?

Answer 21

fetch-decode- execute cycle

Question 22

What does the fetch instruction do?

Answer 22

1) Copy memory address from the program counter
2) Copy the instruction stored in the MAR address to the MDR.
3) Increase the program counter to point to the address of the next instruction, ready for the next cycle.

Question 23

What does the decode instruction do?

Answer 23

The instrcution in the MDR is decoded by the CU. The CU may then prepare for the next step e.g by loading values into the MAR or MDR.

Question 24

What does the execute instruction do?

Answer 24

The instruction is performed. This could be:

Load data from memory, write data to memory, do a calculation or logic operatio, change the address or halt the program.

Question 25

What does CPU performance depend on?

Answer 25

Clock speed, cores and cache. CPUs with higher clock speeds, more cores or larger caches will have better performance, but will also be more expensive.

Question 26

What is clock speed?

Answer 26

Clock speed is the number of instructions a single processor core can carry out per second. For most computers it will be around 3.5GHz.

Question 27

How does clock speed affect CPU performance?

Answer 27

The higher the clock speed, the greater the number of instructions that can be carried out per second.

Question 28

What are the dangers of having a high clock speed?

Answer 28

Some CPUs can be overclocked to make them run at a higher clock speed than the factory set rate. But it is risky if not done properly as it can make CPUs overheat, causing crashes or permanent damage to the system.

Question 29

What can help a overheated CPU with a high clock speed?

Answer 29

High performance cooling systems

Question 30

How do the number of cores affect the performance of the CPU?

Answer 30

Each core in a CPU can process data independently of the rest. The more cores a CPU has, the more instructions it can carry out at once, so the faster it can process a batch of data. Most smartphones have 4 or more cores.

Question 31

What is a core?

Answer 31

A processing unit found inside the CPU

Question 32

What is cache?

Answer 32

Cache is data storage inside the CPU that’s much faster than RAM.

Question 33

How does cache affect CPU performance?

Answer 33

A larger cache gives the CPU faster access to more data it needs to process.