UPAM and BTAM are the basic access methods for disks and tapes respectively. Because they are of minor importance for small applications, they have become less important. They should always be taken into account when a processing operation is being planned. They include certain functions not available with other access methods. It is often possible to improve performance considerably by using them in preference to other access methods at no detriment to user-friendliness. UPAM, for example, permits random access using the half-page number.
The following advantages apply to both UPAM and BTAM:
a simple interface for the application program
There is only one action macro for DMS for each method. The action required is formulated using current parameters. Every read/write request from the program causes a physical I/O operation.
UPAM and BTAM use shorter path lengths compared with SAM and ISAM, as the blocking and unblocking operations on the records are not necessary.a choice between synchronous and asynchronous I/O operations
asynchronous I/O operations can reduce the runtime of a program considerablyunrestricted access to the characteristics of the storage medium; optimum utilization of these characteristics is possible
chaining of jobs to save SVC calls and processing of files created using other access methods
chaining of I/O operations to reduce system overhead (chained I/O).
Additional advantages with UPAM:
random access (similar to keyed access) using the half-page number
possibility of processing files whose contents are damaged
shareability even when updating
possibility of combining asynchronous I/O calls with eventing
Additional advantages with BTAM:
the block length is freely selectable within the range allowed by the hardware
data carriers from foreign operating systems can be processed.