CPU and Buses Flashcards
Address Line
Used to specify a memory address to be accessed.
Data Line
Carry the actual data.
Control Lines
Tells the receiver what to do with the data.
Bus Contention
An undesirable state in computer design where more than one device on a bus attempts to place values on it at the same time.
Polling
Polling periodically checks the device status by requiring the CPU to stop what it’s currently doing so it can check, which can waste time.
Interrupts
A modern computer system uses interrupts, which allows a device to send a signal to the CPU when its ready (or finished). This invokes an interrupt handler within the operating system, which intercepts the interrupt from the CPU and handles it.
Bit Length
Determines how much memory can be moved and manipulated by the CPU in one operation (the size of the registers/ width of the bus).
Stored Program Concept
Must be converted to binary before processing.
Bit Zero
Right Most / known as the least significant bit.
Control Unit
Governs the activity of the CPU, as well as supplying the ALU with data and telling it what to do.
Arithmetic Logic Unit
Performs bit manipulations and numeric operations.
Registers
Faster than storing things in RAM.
Have different names and specific uses.
Holds temporary data while operations are being carried out by ALU.
Instruction Pointer/ Program Counter
Holds the address of the next instruction in memory.
Instruction Register
Holds instruction currently being executed.
Memory Address Register / Memory Buffer Register
Used by CPU to interface with main memory.
Memory Management Unit
Responsible for the translation of virtual addresses used by software to physical addresses used in the memory system.
It also manages storage and retrieval of data from main memory.
Instruction Set Of CPU
Transfer - moving of data
Arithmetic - simple maths like add and subtract
Logic - bit manipulations like AND, OR, NOT
Test - comparing data values and setting status flag
Control - jumps and subroutine calls
Misc - various helper operations
Opcode and Operand
Opcode is instruction, operand is data.
Mode
Part of the instruction which tells CPU where the instruction is. The “modes” it can have are:
Immediate - encoded in instruction (number etc)
Register - stored in register
Direct - in main memory
Register Indirect - specifies a register that holds address of the operand in main memory.
CPU
Control Processing Unit -> fetches, decodes and executes instructions
