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1.3 Hardware and Software 1-5 (CPU - Central processing unit (main…
1.3 Hardware and Software 1-5
Von Neumann Architecture
Arrows represent the wires that carry the information between part
Buses
Buses essentially move data around the computer and send out control signals to make sure everything is properly synchronised.
Addresses and Registers
Addresses indicate where the data is stored (in memory) and registers are needed so that data can be manipulated within the computer while instructions execute on the CPU
types of Addresses and Registers
MAR
memory address register
MDR
memory data register
ALU
arthithmetic and logic unit - Accumulator
PC
Program counter
CIR
current instruction register
e.g. if two numbers are to be added, both numbers must be stored in registers and the result of the addition must be stored in a register
1.the
Program Counter
contains the address of the instruction
2.the address is copied from the
Program Counter
-->
Memory Address Register
3.the instruction is fetched & placed in the
Memory Data Register
4.the instruction comes from the
Memory Data Register
-->
Current Instruction Register
5.the
Program Counter
is incremented
6.Instruction is decoded by
Control Unit
7.The address part of the instruction -->
Memory Address Register
8.The instruction is executed with data moving to/from memory &
Accumulator
via
Memory Data Register.
the fetch execute cycle
To carry out a set of instructions, the processor first of all FETCHES some data and instructions from memory and stores them in suitable registers. Both the address bus and the data bus are used in this process. Once this is done, each instruction needs to be decoded before finally being EXECUTED. This is all known as the FETCH–EXECUTE CYCLE and is the last part of this puzzle.
The CURRENT INSTRUCTION REGISTER (CIR) contains the current instruction being procesed. THE PROGRAM COUNTER (PC) contains the address of the next instruction to be executed.
Fetch
In the fetch–execute cycle, the next instruction is fetched from the memory address currently stored in the Program Counter (PC) and is then stored in the Current Instruction Register (CIR). The PC is then incremented (increased by 1) so that the next instruction can be processed.
This is then decoded so that each instruction can be interpreted in the next part of the cycle.
Execute
The processor passes the decoded instruction as a set of control signals to the appropriate components within the computer system. This allows each instruction to be carried out in its logical sequence.
CPU - Central processing unit
Processor
The component in the computer that fetches, decodes and executes instructions
main memory/RAM
Also known as Immediate Access Store and Primary Memory
The memory in the CPU that is used to temporarily store programs while they are running and data used by these programs. The processor fetches instructions from main memory. Memory is made up of many addressable locations.
Cache
High speed memory in the CPU that is used to store a copy of frequently used instructions and data. Faster access speed than main memory.
Used to improve CPU performance
Clock speed
– Measured in Hertz or cycles per second, the clock speed represents how many instructions per second the processor can execute. The higher the clock speed the faster the CPU can operate.
Level 1 Cache
Cache that is on the processor chip
Level 2/3 Cache
Cache that is on the motherboard, not on the processor
