Disks are sequential access devices. Sequential access is an access method that performs read and write operations in the logical order of records, that is, using information in the order determined by its actual location in the memory. Tape is a typical sequential access device. There is usually a gap between two adjacent physical blocks of the tape. The purpose is to allow the tape drive to easily find the location of the next physical block when accessing the subsequent physical block. .
The operating environment of this tutorial: Windows 7 system, Dell G3 computer.
Disk is a storage device and a sequential access device.
Sequential access is an access method that performs read and write operations in the logical order of records. That is, information is used in the order determined by its actual location in memory. In record files, sequential access is reflected in the order in which records are arranged. If the currently accessed record is R-1, the record to be accessed next time is automatically determined to be R. Sequential access in a streaming file is reflected as a change in the current read-write pointer. That is, after accessing a piece of information, the read-write pointer automatically adds the length of the piece of information to indicate the location of the next access.
Commonly used sequential access devices
Commonly used file storage devices include disks, tapes, optical disks, etc. The characteristics of the storage device determine file access. In order to effectively utilize the file storage device and facilitate the processing of file information, the storage space of the file is usually divided into several physical blocks of equal size. Sequential access devices mean that subsequent physical blocks can be accessed only after the previous physical block is accessed. Tape is a typical sequential access device. There is usually a gap between two adjacent physical blocks of the tape. The purpose is to allow the tape drive to easily find the next physical block when accessing the following physical block. block location.
Extended knowledge:
The external memory of the computer uses a tape-like device. The more commonly used one is called a magnetic disk, which is a round magnetic disk. The disk is packed in a square sealed box. The purpose of this is to prevent the surface of the disk from being scratched, resulting in data loss. With the advent of disks, it has become much more convenient for people to use computers. Not only can they store data processing results in disks, but they can also store a lot of data input into the computer into disks, so that the data can be used repeatedly and avoid duplication of work. . But not long after, people discovered another problem: people wanted to store more and more content on the disk, and it was very inconvenient to store so much information together. This led to the creation of the file system. Only low format will cause great damage to the disk, other reading and writing does not matter.
Disk refers to a memory that uses magnetic recording technology to store data.
Disk is the main storage medium of computer. It can store a large amount of binary data and can maintain data without loss even after power outage. The disk used in early computers was a floppy disk (Floppy Disk, referred to as floppy disk), and the disk commonly used today is a hard disk (Hard disk, referred to as hard disk).
Technical indicators of disk:
The main technical indicators of disk storage include: storage density, storage capacity, access time and data transfer rate.
Storage density: Divided into track density, bit density and area density.
Track density is the number of tracks per unit length along the radius of the disk, in tracks/inch.
Bit density is the number of binary code bits that can be recorded per unit length of the track, in bits/inch.
Area density is the product of bit density and track density, in bits/square inch.
Storage capacity: The total number of bytes that a disk storage can store.
Access time: Access time consists of three types of time: seek time, waiting time, and data transmission time.
Seek time: the time it takes for the disk to locate on the specified track
Waiting time: the time after the seek is completed until the information that needs to be accessed on the track reaches under the head
Data transfer time: The time required to transfer data
Data transfer rate: The number of bytes of data transferred from disk storage to the host per unit time
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