's Time Sharing Option for MVS, adding interactive data processing to a system built for batch
processing of data. In the beginning, TSO was mostly used with IBM 3270
terminals - beasts with a keyboard the size of a C64
, no graphics or national characters and operated in block mode
, i.e. all data on the screen would be transferred at the same time instead of character by character.
The IBM 320 terminal running under TSO would not support scrolling - as the 3270 was/is a screen-oriented terminal,
as opposed to character-based terminals like the DEC vt100. If your screen was full, three asterisks (***) would appear at the bottom of the page - pressing the Enter key another time would clear the screen and continue your output. Fancy terminal IO was possible - a special access method for terminals called TCAM even allowed full screen processing, provided you knew your Assembler.
TSO knew a feature like today's shell scripts or batch files, called .CLIST.
Later on, IBM added SPF, still later ISPF to TSO, adding a somewhat more menu- and mask-oriented user interface.