What Is a Storage Record?

Stored data can be stored files, pages, records, and data items. A storage file is the basic unit for storing data. A database is a collection of one or more storage files.

There are three types of records:

The storage record structure design includes the determination of the content and format of the storage record itself and the determination of the structure (relationship) between the records, and the latter is actually the choice of storage file structure. The structure of the stored file determines the format of the stored records to a certain extent, such as whether the records are variable or fixed length, and whether there are link pointers. So you should choose the storage file structure first.

The structure of the stored file itself is divided into

How to implement the storage of each file on the physical device, the physical designer has to make two decisions: one is to store the entire record as a unit or to divide it into pieces, which is the problem of the division of the record; Is it stored in a continuous physical area as a whole, or is it a clustering of records of closely related different files to be stored in a continuous physical area, that is, the clustering of records.

The storage recording device includes internal memory, external memory and optical storage device ^[2] .

Internal memory

Internal memory, also called main memory, is used to store programs and data that can be read and written directly by the CPU. It can be divided into random read / write memory RAM and read-only memory ROM according to the difference of read / write methods, which are usually made of semiconductors.

The random read / write memory RAM (Randm Access Memory) is readable and writable, and generally stores the program being executed and the processed data. Such as shutdown or power failure. All data stored in RAM will be lost. Therefore, in order to properly save the data in the memory. The results processed by the CPU need to be stored in the external memory in time.

The read-only memory ROM (Read Only Memory) is characterized in that it can only read and cannot write new information, and usually stores some monitoring programs and other basic service programs that cannot be rewritten to manage the machine itself. ROM can store information for a long time, and the stored data will not be lost after shutdown or power failure.

External memory

External memory, also called auxiliary memory, can store temporarily unused programs and data for a long time. External memory cannot be read / written directly by the CPU, but exchanges data with memory. Compared with memory, external storage has the advantages of large storage capacity, high reliability, low price, and long-term storage of data. The disadvantage is that the data read / write speed is slow.

Commonly used external storage are magnetic tapes, magnetic disks (including floppy disks and hard disks), and optical disks.

Floppy drive and floppy

A floppy disk drive is an important component of a microcomputer system. There are two types of floppy drives: 3.5-inch and 2.25-inch. They are used to read and write 3.5-inch / 1.44MB floppy disks and 2.25-inch / 1.2MB floppy disks. Compared with 2.25-inch floppy disks, 3.5-inch / 1.44MB floppy disks are small in size, large in capacity, and easy to carry. Therefore, in the standard configuration of current brand machines, there are usually only 3.5-inch / 1.44MB floppy disk drives. 5.25-inch floppy disk drives have been almost Eliminated. The data transfer rate of the 3.5-inch floppy drive is 500KB / S. Spindle speed is 300rpm or 360rpm. The track-to-track access time is 3ms, and the average access time is about 90ms.

Corresponding to the size of the floppy disk drive, floppy disks are also divided into 5.25 inches and 3.5 inches. The 1.44MB 3.5-inch floppy disk has 80 tracks on each side and 18 sectors.

Hard disk drive

At present, the hard disks used in the microcomputer system are all Winchester, and are composed of a Head Disk Assembly and a Print Circuit Board Assembly (PCBA) which are encapsulated in a cast aluminum colloid. The warm disk is a kind of magnetic disk storage with a movable head and fixed platters. There are two main drive methods for head positioning: stepper motor drive (deprecated) and voice coil motor drive.

Mobile storage

With the popularity of mobile office, the demand for mobile storage is also increasing, and mobile hard drives using USB interfaces. Because it has the same large capacity, small size, and easy carrying as desktop hard drives, it has gradually become the product of choice for mobile storage. Its common capacity is 4GB. 40GB, 60GB, 80GB, etc., comply with USB2.0 standard.