A Level Computer Science AQA - Fundamentals of Computer Organisation and Architecture - Paper 2 Flashcards
What is meant by the processor (sometimes referred to as the CPU)?
The part of the computer system that processes data by executing program instructions
What is meant by the processor instruction set?
- The list of low level operations that can be executed by a processor
- An instruction set is processor specific
For the processor to be able to execute a program, what must first happen?
The program instructions must first be transferred from secondary storage to main memory, from where they are fetched, decoded and executed
Describe main memory
- Main memory is memory that can be accessed directly by the processor
- Each memory location has a unique physical address, which is a number used to locate that memory location and access its contents
What are the two types of main memory?
- RAM (Random Access Memory)
- ROM (Read Only Memory)
What is meant by a type of memory being volatile?
When power is switched off, all data and instructions stored in the memory are lost
Describe RAM (Random Access Memory)
- RAM is used to hold all of the data and instructions that are currently being processed
- Each location can be accessed directly
- The processor can read and write to it
- It is usually volatile
Describe ROM (Read Only Memory)
- It is non-volatile
- It is written by the computer manufacturer
- Usually stores the BIOS (Basic Input Output System)
What is meant by a bus?
A set of parallel lines that are used to connect together components internal components in order to pass signals between them
Why do buses consist of multiple lines?
So that multiple bits can travel at the same time allowing data to be transferred quickly between components
Name the three types of bus
- Address bus
- Data bus
- Control bus
Describe the address bus
- Carries address locations of stored data from the processor to main memory and input/output controllers
- Unidirectional (one way connection from processor to address bus and one-way connection from address bus to main memory and to the I/O controllers)
- In general, if the width of the address bus is expressed as n bits, then there are 2ⁿ numbers that can be used to address memory locations
Finish the sentence:
The width of the address bus refers to its number of parallel lines, which determines …
determines the number of bits that can be used to form an address of a memory location
Describe the data bus
- Carries data to and from the processor, main memory, and input/output controllers
- The data bus is bidirectional (allows a two-way connection between internal components of the system)
- In general, if the width of the data bus is expressed as n bits, then n bits can be transferred at one time
Finish the sentence:
The width of the data bus refers to its number of parallel lines, which determines …
determines the number of bits that can be transferred in one operation
Describe the control bus
- Carries control signals that coordinate the operation of the components
- The control bus is bidirectional (there are two way connections between the components that the control bus connects)
The control bus carries control signals that coordinate operations that take place inside a computer system.
Give 2 things that a control signal can be used to do.
- Synchronise communication between the components using clock pulses
- Specify the type of data that is being transferred via the other buses (i.e, data values, instructions or addresses)
Give 2 examples of control signals that a control bus might carry.
- Bus request: Signifies that a component needs to access a bus
- Interrupt request: Signifies that an error or exception has occurred that requires the attention of the processor (CPU)
Name the two common system architectures
- Von Neumann architecture
- Harvard architecture
What are the key properties of the Von Neumann architecture?
- Both program instructions and data are stored in main memory and moved between memory and processor when needed by the processor
- The same address and data buses are used in the process of transferring instructions and data between main memory and the processor
What does the Von Neumann architecture consist of?
Consists of:
- a processor
- a memory unit that can communicate directly with the processor
- connections for input and output devices
- secondary storage for saving/backing up data
What are the key properties of the Harvard architecture?
- The Harvard architecture keeps instructions and data in separate memories
- The processor accesses these memories using separate data and address buses
Where is Von Neumann architecture more common?
It is used extensively in general purpose computer systems
Where is Harvard architecture more common?
Embedded systems such as digital signal processing (DSP) systems use Harvard architecture processors extensively
Name 4 advantages of Harvard architecture over Von Neumann
- Instructions and data can be accessed simultaneously
- Instruction and data memories can have different word lengths
- Avoids possibility of data being executed as coded, which can be exploited by hackers
- Different technologies can be used to implement instruction and data memory
Give one advantage of Von Neumann architecture over Harvard architecture
Allows the processor to run a variety of programs that are not known in advance
Describe the stored program concept
Machine code instructions stored in main memory are fetched and executed serially by a processor that performs arithmetic and logical operations
What is the role of the control unit?
- To control operation of fetch-decode-execute cycle
- To synchronise operations of processor
- To control the transfer of data between registers
- To handle interrupts
Give 2 examples of tasks that the control unit is responsible for
- Decodes instructions to determine what needs to be done
- Sends and receives control signals to and from other components
What is the role of the arithmetic logic unit?
Performs calculations and makes logical decisions
What is meant by the term register?
A very fast memory location within the processor
What is the purpose of the Program Counter (PC)?
Holds the address of the next instruction to be executed by the processor
What is the purpose of the Current Instruction Register (CIR)?
Holds the instruction that the processor is currently executing
What is the purpose of the Memory Address Register (MAR)?
Holds the address of the memory location (in main memory) that the processor needs to access, either to read from or write to
What is the purpose of the Memory Buffer Register (MBR)?
(sometimes also known as Memory Data Register)
Holds the data (data values or instructions) that are read from or written to the main memory
What is the purpose of the Accumulator?
Stores the result of any calculation processed by the ALU