A little knowledge of CPU, disk and memory

         The hardware in the computer only transmits and stores 01 Bit data .CPU Different voltages on both sides , Different results are obtained with the help of semiconductors .  Operate the output voltage and input voltage of the element through language . All functions of the operating system are the scheduling kernel . If you write a program to dock with the kernel , Then the program can run in any version , If not , Will be limited by the version .

         Have their own main method , What can run independently is called the main process . adopt .exe A file called main Method , Re pass main Method calls other methods . Program installation is to fill in the registration form according to the information .

Solid state disk is fast , But it has a service life , high price . The mechanical disk is slow , But there is no service life .

If the power-off data is not available, it is called flash memory , Data in is called permanent storage .

N Extremely 1,S Extremely 0.

The disk gives an initial voltage , Generate corresponding displacement and generate voltage , Read data according to voltage .

There are no sectors in Physics , Sectors are logically divided by the operating system , Each sector of the disk is the same size .

5400 turn / branch 、 Desktop computer 7200 turn / branch 、 The server 10000 turn / branch . Turn around 10ms about . Find a data average on disk 5ms about , Half a turn on average plus the swing of the manipulator .

CPU Read data from memory on average 20ns,CPU Run once on average 0.2ns.

1ms=1000μs=100 ten thousand ns.

CPU Operation can be operated at one time 64 The bit ,CPU The number of bits of the operating system depends on the amount of a single operation .

         The data read from the disk will pass through a filtering device before reaching the memory , Illegal data will form a circuit break , Only legal data can form a channel . There will be location data before the data , The filtering device will judge whether the position data matches . The interference voltage will affect the internal circuit of the filter , Change the circuit , Control whether the data can pass .

Memory functions ：

        CPU Processing speed is too fast , The reading speed can't keep up with ,CPU Equivalent to idling , Waste resources . Memory can read data in batches . If you can support batch data reading , The disk can rotate one circle and get the data , Average 5ms, add CPU The time ratio of reading data from memory CPU It takes less time to read data directly from disk .CPU Not enough storage space , Only one data can be read one data , Time is too long .

The slow opening time of the program is from disk to memory , Running fast is memory to CPU.

CPU Pass address to memory , Memory should put that address back 1 Page total 4096 Bytes of data are passed to CPU

Bit shift , example 12bit,（5,7）, each page 2^7, Yes 2^5 page

The role of the page ： Support batch reading

Cache function ： Reduce waiting time , Improve performance

         In the mainstream CPU in , Generally, the cache is divided into level-1 cache 、 Second level cache 、 Three level cache , And the speed between them decreases , Capacity increases , Reading the information in the L1 cache requires 3 A cycle , And CPU The speed of processing operations is infinitely close , The cycle of reading L2 cache is about 10-15 A cycle , The third level cache takes 50 About a cycle .

Any core can only process one instruction at a time .

Due to the bus , At a certain moment, only one message comes from CPU The instructions of can operate on memory .

Semaphore mechanism

        1、 After the first one is completely processed , Only the second one can read .

        2、 After the first reading , Give the data a semaphore , After the second processing , Modify semaphore , Compare semaphores after the first one is processed , If not, read again .

Disadvantages of cache ： It will cause data coverage

Lock mark ： A lock mark will be added after reading the data , When the data is processed, the lock mark will be notified to be released . Semaphores do not notify , So you need to read the data again .

Saving data with arrays saves space than with variables .

The file is stored on disk , Variables exist in memory .

Sequential file storage can speed up the search , But there may be a problem of space .

Now the storage on disk is sequential storage , But when storing, there will be space left in the storage unit , It is convenient to modify data in the future

Pipelining technology will enable instruction rearrangement to reduce the number of switches , Improve overall performance , But there will be problems with multithreading .