Brief description of CPU

a central processor （CPU,Central Processing Unit）： It is mainly composed of arithmetic unit 、 The controller and the register consist of .CPU It's a very large scale integrated circuit , It is the core of computer operation and control ,CPU Its main function is to interpret computer instructions and process data .

32 Bit structured CPU The data bus width is 32 position , Every time you can transmit 32 Bit data , You can calculate 4 Bytes of data .

64 Bit structured CPU The data bus width is 64 position , Every time you can transmit 64 Bit data , You can calculate 8 Bytes of data .

1 byte (Byte) be equal to 8 position (bit)

CPU The composition of

Arithmetic unit

Including arithmetic logic operation unit （ALU,Arithmetic Logic Unit） And registers , As a whole CPU Command and control center , Its basic function is to fetch instructions from memory 、 Analyze instructions and execute instructions .

controller

The controller consists of program counter （PC,Program Counter）、 Instruction register （IR,Instruction Register）、 Instruction decoder （ID,Instruction Decoder）、 Timing generator （Timing Generator）、 Operating the controller （Control Unit） form .

register

register （Register）, yes CPU Small internal storage areas for storing data , It is used to temporarily store the data and results involved in the operation .

stay CPU There must be at least six types of registers in the ： Instruction register （IR）、 Program counter （PC）、 Address register （AR）、 Data register （DR）、 Accumulation register （AC）、 Program status word register （PSW）. These registers are used to temporarily store a computer word , Its number can be expanded as needed .

32/64 position CPU The specific difference

1. faster . Because if a machine instruction is 32 Bit , that 64 Bit register can take two instructions at a time .
2. Can handle larger numbers .32 The integer range that the bit can handle is ±21 Billion , If you need to deal with numbers that are out of range , You need to store data with two instructions , And you need to use additional instructions to process data .
3. Control more address buses , Addressing larger memory space .（32 Bits can only be used at most 4G Memory , and 64 Bits can theoretically be used 16777216TB Memory ）

CPU Instruction cycle of

Clock cycle ：CPU It is driven by converting the pulse generated by quartz crystal into clock signal , Each high-low level conversion of clock signal is a cycle , We call it a clock cycle .

Instruction cycle ： from PC Pointer read instruction 、 To carry out 、 Go to the next instruction , Form a cycle , This continuous cycle is called CPU Instruction cycle of .

The clock signal is 1GHz Of CPU, Represents the execution of... Per second 10 100 million clock cycles （1G by 10 Of 9 Power , namely 10 Billion ）, Therefore, one cycle of the clock signal is 1/10 Million seconds . And the speed of light is 3×10 Of 8 Cubic meter per second , Namely 3 Million meters per second . So in one cycle , Light can only move forward 30 centimeter .

CPU One or more instructions can be executed in each clock cycle , It depends on the type of processor . Early computer processors and slower CPU Only one instruction can be executed in each clock cycle , Modern processors can execute multiple instructions per clock cycle （ Multicore ）.

One CPU The execution cycle of is to extract the first instruction from memory 、 Decode and determine its type and operands , perform , Then extract 、 Decoding to execute subsequent instructions .

1. Fetch, Take command . First CPU adopt PC The pointer reads the instruction corresponding to the memory address .
2. Decode, Analysis instructions .CPU Decoding instructions .
3. Execute, Execution instruction .CPU Execution instruction .
4. Store, Memory instruction .CPU Save the result back to the register or store the register in memory .

CPU Set of instructions

Our common x86（32 position ）/x64（64 position ） Refer to CPU Set of instructions .

The instruction set is CPU The medium of software directing hardware execution , Each assembly statement corresponds to a CPU Instructions , The set of instructions is called CPU Set of instructions .

64 The program of bit instruction cannot be in 32 Bit machine , because 32 Bit registers can't hold 64 Bit instruction .

The operating system is also a program ,64 Bit operating system uses 64 Bit instruction , Can't be installed in 32 On the bit machine .