# Computing - Computer Organisation and Architecture > Source: https://ollybritton.com/notes/a-level/computing/topics/computer-architechture/ · Updated: 2020-09-28 · Tags: computing, school, safe-to-post-online ##### What is a computer system?? Any device that can take a set of inputs and process them into useful outputs. ##### What are the three key stages in a computer system?? $$ \text{input} \to \text{process} \to \text{output} $$ ##### What are the 4 main components of a motherboard?? * CPU * Main memory * Address, control and data buses * I/O controllers ##### How do components of a motherboard communicate with one another?? Using a bus. ##### What are the three types of bus?? * Control * Data * Address ##### Why can't external devices be connected directly to the processor?? Because the external devices are produced by different manufacturers so they will work differently. ##### Why are I/O controllers neccessary in a motherboard?? So that the motherboard can act as an interface between the device and the computer. ##### What is the main function of an I/O controller?? Converts signals from peripheral devices into a format the computer can accept, and vice versa. ##### What burden does an I/O controller take from the CPU?? The I/O controller manages data flow to and from a device so the CPU can get on with other tasks. ##### What is the control bus?? Sends control signals to and from the processor to I/O controllers and memory. ##### What is the data bus?? Sends data between different components in the CPU. ##### What is the address bus?? Sends memory addressed from the processor to components. ##### What does uni-lateral mean?? Data can only sent one way. ##### What does bi-lateral mean?? Data can be sent both ways. ##### What is a memory read control signal?? Cause data from the addressed location to be placed on the data bus. ##### What is a memory write control signal?? Cause data on the data bus to be written into the address location. ##### What is a bus request control signal?? Indicates that a device is requesting the use of the data bus. ##### What is a bus grant control signal?? Indicates that the CPU has granted access to the data bus. ##### Who sends a bus grant control signal?? CPU. ##### What is a clock signal?? Used to synchronise operations in the CPU. ##### What is a bus in hardware?? A series of wires that transfer data signals between internal components. ##### What are the common number of lines in a bus?? * 8 * 16 * 32 * 64 ##### What is a line in a bus?? One individual wire in a bus. ##### What is a word in computing?? Chunks of equal units in memory. ##### Words can be accessed by?? A unique memory address. ##### What would be the memory capacity in bytes of a machine with an $8$-line address bus and a word length of $8$ bits?? $$ 8 \text{bits} \times 8 \text{lines} = 64 \text{bits} = 8 \text{bytes} $$ ##### What are the common number of words in memory?? * 8 bits * 16 bits * 32 bits * 64 bits ##### What type of direction does a data bus have?? It is bi-drectional. ##### What makes a data bus bi-directional?? Data can be sent both ways along the bus. ##### What is the "width" of a data bus?? The amount of lines/wires it contains. ##### If you have a 16 line bus and a 32 bit word, how many memory access and data transfer operations will there be?? 2 operations. ##### How does bus width affect overall system performance?? Because it affects how many operations there have to be to retrieve memory. ##### What type of direction is an address bus?? Uni-directional. ##### What affect oes the width of an address bus have on the system. It determines the number of maximum possible memory addresses of the system. ##### How many addresses can a 32 bit bus support?? $$ 2^{32} $$ ##### A system supports $256$ addresses. What is the width of its address bus?? $$ 8 $$ --- Olly Britton — https://ollybritton.com. Machine-readable index: https://ollybritton.com/llms.txt