Computer Systems: Chapter 2 (Computer Structure) Flashcards
What are the 3 main parts of the CPU?
- Control Unit
- Arithmetic and Logic Unit (ALU)
- Registers
What is the ALU?
The ALU carries out the calculations and performs the logical operations
What is the Control Unit?
The Control Unit controls all other parts of the processor and makes sure that the program instructions of the computer are carried out in the correct order
What are the Registers?
The Registers are a group of storage locations internal to the processor that hold data being processed, instructions being executed and addresses to be accessed
What do the buses do?
They connect the processor to the memory and input/output devices
What is the Data bus?
The Data bus carries data to and from the processor to the main memory and any other devices attached to the Data bus, and is bi-directional
What is the Address bus?
The Address bus carries the address information from the processor to the main memory and any other devices attached to the Address bus, and is unidirectional
What 5 lines is the Control bus made up of?
The Control bus is made up of the read, write, clock, interrupt, and reset lines
What is the Read line in the Control bus?
The Read line instructs memory to place data from the specified memory address on the Data bus
What is the Write line in the Control bus?
The Write line instructs memory to take data on the data bus and place it in the location specified by the address bus
What is the Clock line in the Control bus?
The Clock line carries a series of clock pulses at a constant rate in order to synchronise all operations of the CPU
What is the Interrupt line in the Control bus?
The Interrupt line sends a signal to the processor from a peripheral device to stop one routine and give control of the processor to the peripheral device
What is the Reset line in the Control bus?
The Reset line returns the processor to its initial state by stopping the current process, saving the contents of the Registers and then resets the system
What is the Fetch-Execute cycle?
It is the way in which the processor takes in an instruction from memory (fetch) and carries out that instruction (execute)
What are the steps involved in a memory Read operation? (4)
- The processor sets up the Address bus with the required memory address
- The Control Unit activates the read line on the Control bus
- The contents of the particular storage location in memory are released onto the Data bus and copied into the processor’s Memory Data Register.
- If the contents are an instruction then it’s decoded and executed
What are the steps involved in a memory Write operation? (4)
- The processor sets up the Address bus with the required memory address by placing a value in the Memory Address Register.
- The processor sets up the Data bus with the value to be written to memory by placing a value in the Memory Data Register.
- The Control Unit activates the write line on the Control bus
- The contents of the Memory Data Register are transferred to the required storage location in the computer’s memory
What is Cache memory?
It holds frequently accessed instructions (which speeds up the fetch execute cycle) to speed up system performance
What is Main memory?
It consists of a number of storage locations, each with a unique binary address, and is split into RAM and ROM
What is Addressability?
It is the method a computer uses to identify storage locations
What is a ‘Word’?
A word is the number of bits that can be processed by the processor in a single operation
What is Random Access Memory (RAM)?
It is the part of the Main memory that holds its data as long as the computer is switched on
What is Read Only Memory (ROM)?
It is the part of Main memory that holds its data even when the computer is switched off
How is the maximum capacity of Memory calculated?
(2^width of address bus) x width of data bus in bytes
What is the order, from fastest to slowest, of the types of memory?
Registers are the fastest, then Cache, then Main Memory, then Backing storage is the slowest
What is Clock speed?
It is the rate at which the Clock generates pulses
What is MIPS?
Millions of Instructions Per Second is a measure of the performance of a computer system
What is FLOPS?
Floating Point Operations Per Second is another measure of the performance of a computer system
What are Application-Based tests?
They are tests which show how a computer system is likely to perform when it is being used to carry out ordinary tasks
Why does increasing Data bus width increase computer performance?
It will increase the number of bits that can be transferred in parallel to and from memory
What effect does the use of Cache memory have on computer performance?
It will mean that the CPU can quickly get instructions and data from Cache memory, instead of accessing the slower Main memory
Why does increasing the rate of data transfer to and from peripherals increase computer performance?
All peripherals operate at slower speeds than the processor, so increasing the rate of data transfer between them will reduce the gap and increase performance
What are 3 trends in computer hardware?
- Increasing Clock Speeds
- Increasing Memory
- Increasing Backing Storage Capacity
What is an advantage of using MIPS?
MIPS measures processor throughput and are independent of other computer components ie hard disk speed
What are the differences between Cache memory and Main memory? (2)
- Cache memory is more expensive per megabyte
* Cache memory has faster access
What would be the effect of adding one new line to the address bus on the maximum addressable memory?
The addressable memory size would double
Why is using Clock speed alone not an effective way to measure computer performance ?
Clock Speed does not take other important architectural features into consideration (such as data bus width)
Why is FLOPS a better measure of system performance that MIPS? (2)
- FLOPS results may be more reliable as logic and arithmetic operations measured are more complex, so would better reflect system performance
- MIPS test may have been performed with small and simple machine instructions, which do not reflect system performance
Why do computers not come with the maximum addressable memory installed?
Most programs do not require maximum RAM to be installed
