In addition to the block terminals used in BS2000, POSIX also supports the character terminals used in UNIX systems. These terminals connect to UNIX multiuser systems and are served by POSIX via network links. A character terminal is emulated when accessing POSIX via a workstation. In the case of UNIX workstations, this is a terminal such as the type 97801.
Block and character terminals differ in their modes of operation:
BS2000 and POSIX commands can be entered from block terminals, however, the input of POSIX commands is subject to certain minor restrictions (see the "POSIX Commands" [1] manual).
Character-oriented processing is not possible in the case of block terminals. Block terminals transfer the entire text input on the screen to the BS2000 computer as a data block. The block terminal itself performs control functions.
In the case of character terminals, every character entered is immediately passed to the UNIX System, and from there transferred and mapped to the screen as a response to the input. The UNIX computer to which the terminal is connected executes control functions, such as cursor movement and uppercase and lowercase lettering. It also buffers the data transferred.
In POSIX, character terminals are treated as files. They have a unique name and can be read from and written to. The same functions as for file access are used for this purpose.
Screen-oriented applications - such as the vi editor in UNIX systems - require character-based operations. Therefore, they can only run if they are started on a character terminal.
Some inputs are terminal-specific, in other words they differ for block and character terminals:
Block terminal | Character terminal |
@@d | CTRL + D |
@@c | CTRL + C |
@@/ | CTRL + \ |
EM DUE | Enter key |
@@z | CTRL + Z |
- | CTRL + S, CTRL + Q, ... |
Segmentation of the screen is not supported in BS2000. The screen always displays its contents from top to bottom. Input and output both occur in the lowest active line. When the screen is full, the contents are moved upwards a line, causing the uppermost line to disappear. Preceding lines can no longer be accessed.