CPU

CPU

1. purpose of the CPU

   • Brain of the computer system
   • Processes data and instructions
   • clock speed, number of cores and cache size change the CPU
   • Von Neumann and Harvard are the 2 main types

2. CU (Control Unit)

   • its in overall control
   • main job: fetching,decoding and execution of program instructions
   • controls flow of data inside the CPU and outside the CPU

3. ALU (Arithmetic Logic Unit)

   • does all the cacualtions
   • + - * /
   • performs logical operations such as AND, OR. NOT
     • And BINARY SHIFTS
   • Contains the ACC (Accumulator)

4. cache

   • is VERY FAST memory in the CPU
     • however slower than the registers and faster than the RAM
   • stores REGULARLY used data
     • can access it quickly next time when needed
   • checks cache first IF NOT it fetches from the RAM
   • lOW CAPICITY and are EXSPENSIVE (compared to the RAM and secondary storage)
   • different levels of cache memory:: L1, L2, L3
     • L1: quickest but slowest capacity
     • L2: slower than L1 but can hold more
     • L3: slower than L2 but can hold even more

5. REGISTERS

   • Von Neumann Architecture
     • PC (Program Counter)
       • holds memory address of the instruction
     • MAR (Memory address register)
       • holds any memory address data about to be used by the CPU
       • The address might point to data or a CPU instruction
     • MDR (Memory data register)
       • Holds the actual data or instruction
         • May have been fetched from memory or waiting to be written to memory
     • ACC (ACCUMULATOR)
       • Stores intermediate results of caculations in the ALU
   • The memory holds the program instructions and the program data
   • REGISTERS: PC, MAR, MDR, ACC

6. FETCH-EXECUTE CYCLE

   • fetch: copy memory address from program counter to MAR
   • decode: instruction in the MDR is decoded by the CU. CU will prepare for next step
   • execute: instruction is performed: load data from memory. write data to memory, do a caculation or logic operation, change the address in the PC, or halt the program

7. CPU Performance

   • clock speed
     • number of instructions a single processor cor can carry out per second (Hz)
     • The higher the clock speed the greater the number of instructions that can be carried out per second
     • some CPUs can be overclocked to makethem run at a higher clock speed that the factory-set rate
     • its risky if not done properly- make CPUs overheat causing crashes or permanet damage to the system.
     • High performance cooling systems are usually needed.