DASD
Direct access storage device (DASD)
- A general term for magnetic disk storage device. The "direct access" means that all data can be accessed directly in about the same amount of time rather than having to progress sequentially through the data.
Space
Disk space is allocated in units called cylinders, tracks, or blocks.
Cylinder
A disk drive contains cylinders. A cylinder is a unit of storage on a count-key-data (CKD) device with a fixed number of tracks.
Track
Cylinders contain tracks, which are circular paths on the surface of a disk or diskette on which information is magnetically recorded and from which recorded information is read. Tracks are in count-key-data (CKD) format, which means that each track contains fields that indicate the start of the track and the space used, followed by records containing three fields:
- The count field defines the length of the record
- The key field contains optional accounting information
- The data field contains the user data
Comments
Post a Comment