Computer Organization & Architecture Flashcards
What is Main Memory used for?
RAM and ROM
Used to store program instructions and frequently used data.
Faster than secondary storage - helps processor execute faster.
What are Buses?
What is a bus width?
Name the three main buses:
Series of parallel wires, connecting internal components together. They allow signals to be passed.
The number of wires in a bus is called the width. The width of a bus is directly proportional to the number of bits transferrable simultaneously.
Three main buses: Address Bus; Data Bus; Control Bus
What is the purpose of the Address Bus?
What is the effect of increasing it’s width?
Used to transport memory addresses - specifies where data is to be sent / retrieved from.
Increasing the width will increase the range of addresses it can specify - further increases amount of addressable memory.
Addition of 1 wire doubles the number of addressable memory locations.
- 1 wire = 2 locations
- 3 wires = 8 locations
Addressable memory location -> portion of memory which can be accessed by its address
What is the Data Bus?
Sends data and instructions to and from different components in the system.
Increasing width of data bus increases volume of data transferable simultaneously.
What is the control bus?
Used to carry control signals which regulate system operation
Clock speed and signal is transferred along the control bus.
What I/O controllers?
Pieces of hardware which control the communication of data between the processor and external hardware.
Describe Harvard architecture.
Computer using two seperate memory locations
- one is used for instructions, the other for data.
Enables giving each piece of memory different characteristics - instructions location being Read-Only - instructions can’t be altered.
Used mainly in embedded systems - digital signal processing.
Explain Von Neuman architecture
Both instructions and data are stored together in memory - performs worse than Harvard - shared buses.
Used in everyday general-purpose machines.
What are devices using the Stored Program Concept known as?
“Serially fetching and executing machine code instructions stored in main memory by a processor that performs arithmetic and logical operations”.
Allows for one set of instructions to be swapped out for another.
Based on Von Neuman or Harvard.
What are the 3 main components of a CPU?
Arithmetic Logic Unit
- performs logic operations (OR, AND etc.)
Control Unit
- controls various components of CPU. Controls fetch-execute cycle.
Registers
- small storage locations for temporary data.
Name the special purpose registers and their uses.
PC - Program counter - holds memory adress of next instruction in FE cycle
CIR - Current Instruction Register - holds instruction currently being executed.
MAR- Memory Address Register - holds memory address of memory location that is to be read from / written to.
MBR- Memory Buffer Register AKA MDR- Memory Data Register - holds contents of memory location read from / data to be stored
Status Register - contains no. bits - values can change (indicates occurance of interrupt)
What happens in the Fetch stage of the FE cycle?
Next instruction to execute is frtched from main memory
1 - content of PC copied to MAR
2 - content of MAR transferred to main memory via address bus
3 - instruction sent from Main Memory to MBR via data bus
4 - PC incremented by 1
5 - content of MBR copied to CIR
What happens in the Decode stage of the FE cycle?
1 - content of CIR decoded by Control Unit
2 - decoded insteuction split into opcode and operands.
What happens in the Execute stage in the FE cycle?
1 - data required by instruction fetched
2 - instruction carried out
3 - results of calculations stored in GP registers or main memory
Status register then checked for interrupts before moving back to execute stage
What is Opcode?
What is Operands?
Opcode - Specifies the operation to carry out.
Operands - Data on which the operation is performed.
What is the processors instruction set?
Group of instructions that a processor can carry out. - not compatable with all processors.
Instructions usually stored in machine code consisting of opcode and operands
Opcode - specifies type of operation to be carried out
Opprrands - pieces of data on which operation is performed.
What are addressing modes?
One bit inside machine code usually assigned to the addressing mode in use - intermediate or direct.
Intermediate - value specified in opperand to be treated as the actual value.
Direct - value specified in operand signifies memory address, not value.
What is logical shifting?
Operation performed with binary numbers which involves shifting all the bits in a number (doubling or halving) specified number of positions to the right / left
Logical shift to ledt by 3 bits - add 3 0’s to to end of number
What are interrupts
Signal sent to processor by another component requesting attention. - can also be software.
What happens when the processor recieves an interrupt?
Status register changes between execution and fetch in the FE cycle.
They are handeled by vectored interrupt method.
- Processor stops current program and places one of registers on system stack - saving the ‘volatile environment’.
- loads appropriate input service routine - series of instructions for handling specific interrupt.
- restores volatile environment & resumes execution
What factors affect the performance of the processor.
Number of cores - each core can do an FE cycle
Cache memory - fast memory - reduces data travel time
Clock speed - more FE cycles in same timeframe
Word length - word is group of bits treated as single unit - length of word is number of bits assigned
Address bus width - increases number of addresses that can be specified
Data bus - increase volume of data transferred at a time
