1. Sec (2.3)
Program Execution

2. Program Execution
In the CPU we have CU and ALU, in CU there are two special purpose registers:
Instruction Register
Program Counter

3. The architecture of the machine described in Appendix C

4. Program Execution Instruction Register
Is used to holed the instruction being executed
Program Counter
Contains the address of next instruction to be executed

5. Program Execution
CU performs its job by continually repeating an algorithm that guides it through a 3-steps process known as the Machine Cycle
The steps are:
fetch
decode
execute

6. In fetch step:
the CU requests that main memory provide it with the instruction that is stored at the address indicated by the program counter
Each instruction in our machine is 2 bytes long, this fetch process involves retrieving the contents of 2 memory cells
The CU places the instruction received from memory in its instruction register and then increments the program counter by 2 so, it contains the address of the next instruction stored in memory

7. Decode step: The instruction new in the instruction register
The CU decodes the instruction, which involves breaking the operand field a proper component based on the instructions op-code

8. Execute step:
The CU executes the instruction by activating the appropriate circuitry to perform the requested task

9. Decoding the instruction B258

10. Cache memory: There is a cache in CPU which takes the data from memory
Small memory and faster in accessing.
It is between CPU and RAM
It contains the information and instructions which are commonly used