07 Computer Organsation And Architecture Flashcards
What is a computer system?
Any device that can take a set of inputs and process them into useful outputs
What is the CPU and what are its components?
The central processing unit
It is made of the Processor Main memory Address, control and data buses Input/Output (I/O) controllers
What are I/O controllers?
An interface between the device and the computer
What is a device driver?
Software that directly interacts with the I/O controller
It converts signals from the device into a format the computer can process and vice versa
It receives I/O requests from the CPU, and then sends control signals to the device it is controlling
It also manages the data flow to and from the device, freeing the CPU to get on with other tasks
Must be installed when you use a new device
What is a bus?
A series of wires that transfer data signals between internal components
What is the control bus?
Sends control signals between each I/O controller and the processor as well as between the processor and memory
Control signals include memory read and write and clock
What is the data bus?
It is bi directional as data can be sent both ways along it
The width is defined by the number of wires or line it has
It affects system performance
What is the address bus?
It carries the address of a memory location in one direction from the processor to I/O controllers and memory
The width of the address bus determines the maximum possible memory addresses of the system
A 32 bit bus can carry 2^32 addresses
How is memory divided?
Into equal units called words
What is main memory?
It stores data and instruction that are to be processed
Number of memory addresses is constrained by the width of the address bus
The smallest addressable unit is a word
What is stored program concept?
When computers are designed to allow data and instructions to be stored in order for it to perform different tasks at different times
Machine code instructions are loaded into main memory to be executed by the processor and they are fetched one at a time to be executed immediately in order
What is von Neumann architecture?
Most common implementation of the stored program concept
Instructions and data are stored in a common main memory and transferred using a single shared bus
What is Harvard architecture?
The data and instructions are separated into different memories using different buses
Program instructions and data don’t compete for the same bus and may be stored in unequal quantities
Different sized memory spaces and word lengths can be used for data and instructions
What is the processor and its components?
It controls, calculates and executes instructions
Arithmetic Logic Unit Control Unit Clock General Purpose Registers Dedicated Registers
What is the arithmetic logic unit?
The problem solving part of the computer
It performs arithmetic (+ -), logical (AND, NOT) and shift (move bits to left or right) operations on data
What is the control unit?
The part of the processor that coordinates the activity of all the other components
Instruction accepted and decoded
Separate steps such as fetching the address of data, and fetching the data itself from memory, are identified
Each step is synchronised with a regular pulse from the system clock
What is the system clock?
A series of regular ON/OFF signals that synchronise the operations of the processor components
What are general purpose registers?
Locations of super fast memory that temporarily store results from the ALU
Processor can access and reuse this data
Some processors have a single general purpose register called the Accumulator
What are dedicated registers?
Program Counter - Holds the memory address of the next instruction
Current Instruction Register - Holds the current instruction
Memory Address Register - Holds the address in memory where the processor is required to fetch or store data from or to
Memory Buffer Register - Temporarily holds data moving between the processor and main memory
Status Register - Holds information about the current state of operations. Used to overflow or detect errors
What is the fetch execute cycle?
- Next instruction which is stored in the program counter is copied to the memory address register. The program counter is then incremented by one.
- Memory address register sends it to memory using the address bus. The address bus only sends one way.
- The main memory takes the address and looks at the instructions and sends it to the processor along the two way data bus into the memory buffer register and the memory data register.
- It is then passed onto the current instruction register. This is the end of the fetch as the data is then decoded and executed
- The data is split into two parts, the opcode and the operand. The opcode is the operation part (+ - ) and the operand is the thing that the opcode is going to work on.
- The operation is carried out in the Arithmetic logic unit in the execute part of the cycle. The status register is then updated after every instruction to show flags depending on whether the result is; Negative, positive, overflow, under flow etc.
- The results of the process is then stored in the accumulator and the cycle returns to step one.
What improves processing speed?
Cache - Small amount of super fast memory that is frequently used by the processor (higher cache)
Number of cores - More processor can be linked together on a single chip allowing more instructions to be executed
Address and data bus width
Word length - Amount of data that CPU can process simultaneously
What is assembly language?
A code where mnemonics are used to represent the operation codes and addresses
What is operation code (opcode) and operand?
Opcode - The actual command the processor needs to carry out
Operand - One or more items of data that are used in the instruction
