Modern computer 1. CPU only reads data from memory , hard drive data by the DMA ( the IO memory data exchange with devices directly dealing with memory) manner.
2.CPU bus (BUS) Cycle:
T1: sending address, the address bus
T2: Undo address bus, ready to receive
T3: data is read into the data bus
T4: the end of the bus cycle
The higher the computer clock speed, the shorter the clock cycle, less time consuming and thus appears high performance.
3. Data Bus: responsible for reading and writing data, the data bus width determines the transmission speed. A data bus 8 takes a byte, a 16 byte fetch two.
16 machine for non-aligned (word-aligned address is divisible by 4) of the word, requires two cycles to read, so that the memory alignment is very important.
