Low Level Operations And Structure Flashcards
What is the purpose of the ALU during program execution?
To carry out calculations and make any logical decisions such as comparing two values
What is the purpose of the registers during program execution?
The registers are used if the instruction requires that data be temporarily stored during processing.
Some are for general use whilst others have a specific role such as the program counter which stores the address of the next instruction to be fetched.
What is the purpose of the control unit during program execution?
Responsible for overseeing all operations within the processor. These include;
Timing each event using the computer systems clock.
Initiating the transfer of data along the data bus by activating the read and write lines of the control bus
Interrupting the processor if another task (process) needs dealing with
Telling the ALU how to respond to various instructions.
What steps are involved in the memory read operation?
- The memory address of the data to be fetched is placed in the memory address register (MAR)
- The read line on the control bus is activated by the control unit
- The data is located at the memory address specified by the address bus and is sent along the data bus to the memory data register.
What steps are involved in the memory write operation?
- The memory address of the data to be fetched is placed in the memory address register
- The data to be written is placed in the memory data register (MDR)
- The write line on the control bus is activated by the control unit
- The data is sent along the data bus and stored in the memory address specified by the address bus.
How has CPU technology developed since Von Neumanns original design?
- Buses have widened - allowing for more memory addresses and more data stored on these addresses
- Multi core processors allow more than one instruction to be processed at one time. This allows them to effectively run more than one program at one time e.g running a JavaScript program in a web page whilst playing an embedded video
- Faster types of memory are used to predict and store instructions to be executed through wider buses and being located closer to or within the processor.
What are some of the differences in functionality between peripheral devices and the CPU?
Peripherals - Use Different voltages Transfer data differently Use serial transmission Can be analogue devices Transfer data at different speeds
How does an interface compensate for the differences between the CPU and peripheral devices?
Converting an analogue to a digital signal and vice-versa
Converting serial transmission (one bit being sent down a single wire) to parallel data (multiple bits being sent down multiple wires simultaneously) for transfer down an internal bus
Temporarily storing data in a buffer until a slower peripheral device is ready to receive it
Using status signals to ask the current state of an external device
What is an emulator?
An emulator is a program that imitates the behaviour of another computer system - usually used to test circuits and computer systems before they are built or to simulate old systems such as games consoles
What is meant by a mobile device?
A notebook, smartphone or tablet
What is a virtual machine?
A type of emulator that recreates a complete substitute of a full computer system.
These may be cloud based and purchased on a subscription basis.
What is the function of each CPU bus?
Data Bus - To carry data to and from the registers and into memory it is bidirectional.
Address Bus - Used to specify memory locations where instructions/data are stored. Unidirectional.
Control Bus - Used by the CPU to communicate with devices within the computer. Bidirectional.
What steps are involved in the fetch execute cycle during program execution?
- The memory address of the next instruction to be fetched is placed in the memory address register (MAR)
- The read line of the control bus is activated by the control unit
- The instruction is located at the memory address specified by the address bus and is net along the data bus to the memory data register
- The instruction is transferred to the instruction register, where it is decoded and executed
What is Unicode?
A character encoding standard used for the representation of 65536 characters
This means that it can represent a wide range of character sets
Bit Depth
The number of bits used to store each pixel in an image
