Storage system overview

One . The hierarchy of the storage system

• The storage system ： Store two or more types of memory , With hardware , Software or hardware and software are connected together , And manage them .
• In the hierarchy of the storage system , The closer to the upper layer of memory, the faster , The smaller the capacity , The higher the price per unit of storage capacity .
• In the storage system , Through the collaborative management of storage , Make the system display the optimal characteristics to the outside world , namely ：（1） Make the access speed of the computer close to CPU The speed of （ The speed of the fastest memory in the system ） （2） Make the main memory capacity used by programmers close to the capacity of external memory .（3） Make the storage price per unit capacity of the entire storage system close to the price of external storage

Two . Memory classification

1. Classified by the media on which the information is stored

• Semiconductor memory
• Disk memory
• CD-ROM

2. Classified according to the use in the computer

• Main memory
• Cache
• Control memory
• External memory

3. Classified according to the volatility of stored information

• Semiconductor random access memory RAM（Random Access Memory）： After power failure, the stored information will be lost
• Semiconductor read only memory ROM（Read-Only Memory）： The information stored after power failure will not be lost

4. Sort by access mode

• RAM： The access time is independent of the physical address of the storage unit
• Sequential read-write memory ： Can only be accessed sequentially by the physical address of the storage unit

5. Classified according to the read-write function of the memory

• Read / write storage area
• read-only memory （ROM）

3、 ... and . Memory performance index

1. storage capacity
2. Memory speed
3. reliability
4. Power waste
5. Price