direct access device

They will certainly need to be on a direct access device.

Some direct access devices have available storage areas starting from 00 000 or 00001, and addressed by a simple number.

Initialize the file area on the direct access device.

The following calculations assume that indexes are stored on a direct access device.

The former will tend to require an indexed sequential file on a direct access device.

This depends mainly on the size of the record and the operating speeds of the direct access device in question.

Record-oriented filesystems can be supported on media other than direct access devices.

Self-indexed files will need little or no prior formatting of the direct access device on which they are to be stored.

Because of the way in which direct access devices operate, it is not normally necessary or desirable for the lowest-level index to point to every record.

Although technically possible on magnetic tape, logarithmic searches are too slow to be economic, so they are normally only considered for direct access devices.

BDAM "consists of routines used in retrieving data from, and storing data onto, direct access devices.

System data, in the form of "track capacity tables", are available for calculating the TTRN from a block number, for any direct access device type.

All the common direct access devices, whether disk, semiconductor 'disk' or mass storage device, have a track concept that is important in deciding on the best arrangement of indexes.

The advantage of being able to store such a file on a direct access device in addresses which are directly related to the key then has to be balanced against the waste of space involved.

Records will be read into primary storage, their keys will be transformed by the algorithm being used, and if the address the algorithm produces is free they will be stored in that address on the direct access device.

EXCP is sometimes confused with a direct access storage access method, but it is not for direct access devices exclusively; rather, it is a general purpose low-level device access interface which supports any legacy device type and any legacy dataset organization.