1. The Central Processing Unit
CPU
The Central Processing Unit

2. CPU
It just processes data, be it:
Searching
Sorting
Calculating
Decision making
Needed for everything you do on a computer

3. First
OS loads everything into memory (RAM).
Program
Data

4. Fetch
CPU gets data and instructions (program) from main memory (RAM) and stores in it’s own memory (Registers)

5. Decode Instructions are worked out by the CPU
Different CPUs have different instruction sets
CPU gets ready to do the instructions

6. Execute Instruction is carried out on the data in the CPU’s registers
Result is stored in another Register
Then CPU is ready for another fetch

7. A “borrowed” diagram is worth 1000 words…

8. What is inside a CPU?

9. Control Unit Controls input and output of data
Controls flow of data inside CPU
Organises the fetch/execute cycle

10. Immediate Access Store
The internal registers.
Only holds the data needed for the
instructions
Hard drives are very slow but holds loads of data
RAM is slow, and holds a middle amount of data
IAS is very fast, but holds tiny amount of data

11. Arithmetic & Logical Unit
Processes data by manipulating or changing it.
Arithmetic part
Performs calculations (1+1=2)
Logical unit
Performs logical operations and comparisons (is 1 < 3?)

12. Clock speed A CPU can only ever do one thing at once.
So how can you run Word while listening to iTunes?
Each cycle of the fetch/execute is one instruction
1 cycle per second is a hertz (Hz)
1GHz = instructions per second
Faster CPU means less time for each instruction to complete

13. Faster always better?
Heat
Power
Performance
Architecture

14. Number of cores Dual core means two processors
Can do twice as much in a second than just one processor… in theory
Improved performance (but not doubled?)

15. Cache
No point having a fast processor if there’s no data for it to process.
The more cache the more data can be stored closer to the CPU on fast memory
If data isn’t in cache the CPU will look at the ram, but this is really slow so takes lots of time

16. Questions
1. My laptop has a Intel Core i3 running at 2ghz, it’s faster than your school desktops. Explain.
2. Describe the considerations in picking a laptop’s CPU.
3. Describe the considerations in picking a server’s CPU.
4. Which is the fastest i7 3 ghz pentium or am i5 AMD gHZ.