The Central Processing Unit CPU The Central Processing Unit

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

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

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

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

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

A “borrowed” diagram is worth 1000 words…

What is inside a CPU?

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

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

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?)

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 = 1 000 000 000 instructions per second Faster CPU means less time for each instruction to complete

Faster always better? Heat Power Performance Architecture

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?)

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

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 2.3gHZ.