The data to be processed by programs is generally collected in files. In BS2000, however, the programs themselves, both the source programs and the load modules, are regarded as files. In order to process their data, users must be able to access their files at any time. The Data Management System (DMS) provides them with support for all functions relating to file access, file management and file maintenance.
The information (data) to be processed by a system is collected into various units. The smallest addressable unit is the byte and the smallest unit which can be transferred is the physical block which, on disks, has a fixed length and is called a PAM page (section "Blockformats for disk files").
Logical units are: character, field, record, file and logical block (= data block). The character is the smallest logical unit and corresponds to the byte. A field may contain one or more characters. Fields form the record, which is the basic element of a file. The file, finally, is the sum of the records which it contains.
The system (input/output devices, etc.) knows nothing about the record, which is a logical processing unit. The connecting link between the data storage devices and the transfer/processing devices is the data block. This is the transfer unit and may, for example, consist of one or more standard blocks. Standard blocks (PAM pages) have a specific format and length and can be used for disk and tape files. Nonstandard blocks may be used only for tape files (see section "Block formats for disk files" and section "Blockformats for tape files").
The data block may contain one or more records which may extend over one or more PAM pages.