CPU 1.1

Question 1

what is a computer

Answer 1

a machine that takes data, processes it and outputs it

Question 2

what does CPU stand for

Answer 2

-central processing unit

Question 3

purpose of the CPU

Answer 3

-to fetch, decode and execute instructions
-take an input, process data and produce an output

Question 4

what is hardware

Answer 4

-the physical parts that makes up your computer system

Question 5

what is software

Answer 5

-software is the programs or applications that a computer system runs

Question 6

what are embedded systems

Answer 6

a computer system with a single function, inside a larger mechanical unit

Question 7

examples of embedded systems

Answer 7

washing machines, dishwasher

Question 8

benefits of embedded systems

Answer 8

-far smaller than general computers
-cheaper to produce
-more reliable than general computers

Question 9

what is the control unit

Answer 9

-sends signals to control how data moves around the CPU and to other parts of the computer system
-decodes instructions, allowing for the fetch decode execute cycle

Question 10

what is the arithmetic logic unit

Answer 10

-performs arithmetic operations

Question 11

examples of what the ALU does

Answer 11

-completes simple addition and subtraction, compares the size of numbers and can do multiplications and divisions using repeated addition and subtraction
-performs logic operations and binary shifts

Question 12

where is the accumulator

Answer 12

in the ALU

Question 13

what is the cache and how does the CPU use it

Answer 13

-very small, very fast memory in the CPU
-stores frequently used data and instructions so the CPU can access it quickly the next time it is needed.
-CPU can access data stored in the cache much faster than if retrieved from RAM

Question 14

what happens when the CPU requests data

Answer 14

-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 15

what are the different levels of caches

Answer 15

L1, L2 and L3.
-L1 is the quickest but has the lowest capacity
-L2 is slower than L1 but can hold more
-L3 is slower than L2 but can hold more

Question 16

what is von neumann architecture

Answer 16

-it describes a system where the CPU runs programs stored in memory. Programs consist of instructions and data when are stored in the memory addresses

Question 17

what is the program counter

Answer 17

-it holds the memory address of the next instruction to be executed in memory

Question 18

what is the accumulator

Answer 18

-it stores intermediate results of calculations in the ALU

Question 19

what is the MAR

Answer 19

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

Question 20

what is the MDR

Answer 20

-the memory data register holds the actual data or instruction. This may have been fetched from memory, or be waiting to be written to memory

Question 21

what is the fetch stage

Answer 21

-copy memory address from the program counter to the MAR
-instruction is fetch from the memory/ the address in the MAR
-copy the instruction stored in the MAR address to the MDR
-increment the program counter to point to the address of the next instruction, ready for the next cycle

Question 22

what happens at the decode stage

Answer 22

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

Question 23

what happens at the execute stage

Answer 23

-the instruction is performed
This could be:
-loading data from memory
-writing data to memory
-doing a calculation or logic operation (using the ALU)
-changing the address in the PC, or halt the program

Question 24

what factors affect CPU performance

Answer 24

-clock speed
-number of cores
-cache size

Question 25

what is clock speed and how does it affect CPU performance

Answer 25

-this is the number of instructions a single processor can fetch, decode and execute per second measured in hertz (Hz). (usually around 3.5 GHz)
-the higher the clock speed, the greater the number of instructions that can be carried out per second

Question 26

what is number of cores and how does it affect CPU performance

Answer 26

-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

Question 27

how does cache size affect CPU performance

Answer 27

-the cache is data storage inside the CPU that’s much faster than RAM
-bigger cache can store more frequently used instructions or data, fewer fetch cycles from memory

Question 28

overclocking

Answer 28

-Some CPUs can be overclocked to make them run at a higher clock speed than the factory-set rate, but is risky if not done properly and can make CPUs overheat, causing crashes or permanent damage to the system. High performance cooling systems are usually needed(water cooling)

Question 29

what is an internal clock

Answer 29

-it provides pulse at a constant rate to synchronise components

Question 30

what are registers

Answer 30

-they are tiny, super fast pieces of onboard memory inside the CPU each with a very specific purpose

Question 31

purpose of registers

Answer 31

-very fast memory
-which the CPU can access extremely quickly