(4.7) Fundamentals of computer organisation and architecture Flashcards
The role of the processor
- Executes program instructions in order to run applications
The role of the main memory
- Includes ROM and RAM to store program instructions and frequently used data
- Faster than secondary storage, so storing frequently used data in RAM or ROM helps the processor to execute instructions quickly
The role of buses (general)
- Series of parallel wires that connect internal components of a cs, allowing signals to be passed between them
- No. of wires of bus = width
Has a direct relationship to the number of bits that can be transferred simultaneously by the bus
The role of the address bus
- Used to transport memory addresses, specifying where data is to be send to or recieved from
- Increasing the width of the address bus increases the range of addresses that it can specify, hence increasing the amount of addressable memory
- Adding a single wire doubles the number of addressable memory locations
1 wire in address bus = 2^1 =2 addressable memory locations
2 wires = 2^2 =4 addressable memory locations
3 wires = 2^3 = 8 addressable memory locations
The role of the data bus
- Sends data and instructions to and from the different components of the cs
- Increasing the width of the data bus increases the volume of data that can be transferred at one time
The role of the control bus
- Used to carry control signals that regulate the operation of the cs
- Carries the computers clock signal
The role of the I/O controllers
- (Input/output controllers) are hardware that control the communication of data between the processor and external hardware devices (e.g. keyboards, mice, monitors)
Harvard architecture and where its typically used
Harvard architecture
* Processor uses two seperate memory locations (one for instructions, one for data)
* In this way, it can give each piece of main memory different characteristics, e.g. memory used for instructions could be read-only so that instructions cannot be altered
Harvard architecture is often used in embedded systems such as digital signal processing
Von neumann architecture and where its typically used
Von neumann
* both instructions and data are stored together in the same memory
* These systems often perform worse because of this
Von neumann architecture is often used in everyday general-purpose computer systems, e.g. laptops and smartphones
The concept of addressable memory
The concept of storing data and instructions in memory with discrete, unique adresses
The stored program concept
Machine code instructions stored in main memory are fetched and executed serially (in order) by a processor that performs arithmetic and logical operations
The processor: Arithmetic logic unit (ALU)
The processor
The ALU performs arithmetic and logic operations (e.g. addition, subtraction, AND, XOR, etc)
The processor: Control unit (CU)
The processor
The control unit is responsible for controlling the components of the processor and the fetch-execute cycle
The processor: The clock
The processor
The system clock generates a timing signal which changes at a regular frequency
The signal is used to synchronise communication between the components of the processor and the rest of the cs
The processor: General purpose registers
The processor
Registers in general are small storage locations used to hold data temporarily, with high read and write speeds
General purpose registers can be used as storage for any data that is required by instructions during execution
The processor: Program counter register (PC)
The processor
Used to hold the memory address of the next instruction to be executed in the fetch-execute cycle
The processor: Current instruction register (CIR)
The processor
Holds the instruction that is currently being executed by the processor
The processor: Memory address register (MAR)
The processor
Stores the memory address of a memory location that is to be read from or written to
The processor: Memory buffer register (MBR)
The processor
Also called the memory data register (MDR).
Holds the contents of a memory location (so the data) that has been read from or data that is to be stored
The processor: Status register (SR)
The processor
Contains a number of bits, the values of which can change to indicate the occurance of an interrupt
The Fetch-Execute cycle: Fetch
The next instruction to execute is retrieved from main memory
1. The content of the PC is copied to the MAR
- The content of the MAR is transferred to main memory by the address bus
- The intruction is sent from main memory to the MBR by the data bus
- The PC is incremented by one
- The content of the MBR is copied to the CIR
The Fetch-Execute cycle: Decode
The fetched instruction is decoded
1. The content of the CIR is decoded by the control unit
- The decoded instruction is split into two parts: opcode (Specifies the operation to carry out) and operands (data on which the operation is performed)
The Fetch-Execute cycle: Execute
The instruction is carried out
1. Any data required by the instruction that isn’t present in registers is fetched
- The instruction is carried out
- Results of any calculations are stored in general purpose registers or main memory
Processor’s instruction set
a processor’s instruction set is the group of instructions that it carries out
* Each type of processor has its own instruction set, so instructions for one processor may not be compatible with other processors
* Instructions are usually stored in machine code and consist of two primary parts: opcode and operands (at least 1)
* Opcode specifies the type of operation to be carried out (e.g. additon, subtraction, logical shifting, etc)
* Operands are the pieces of data on which the operatio is performed
