ICL 7500 series

A narrow operator's console with indicators, rotary-switch and modem control switches was implemented below the VDU screen bezel.

This gave the engineer full capability of reading and writing registers or memory and single-stepping machine code or CPU microcode.

The keyboards were separate input/output devices whose data was decoded by the operating software to update the screen display or trigger actions by the system.

Security identifiers (Personal Identity Device, or PID) based on magnetically-coded pens with a reader at the top right corner of the keyboard unit could be used to provide levels of access-privilege to users.

Early 7561/1 VDUs had simple composite-video inputs, while the updated 7561/2 VDU had improved display tubes and interlaced scan.

Similar functions also allowed the screen attributes to be amended in bulk, such as setting blocks of text to flash or to be displayed in italics.

Operational software was referred to as a Terminal Executive (TE), and would vary depending upon the functions required, mainframe connection and communications protocol employed.

Variants for communication with IBM mainframes, X.25 networks and the Counter Terminal System for Anglia Building Society and Local Government sector were examples.

A separate development was the WORDSKIL word-processor system which was based upon 7502 hardware with dual or quadruple single-density floppy disks, portrait-format VDU and the Qume "Daisy-wheel" printer.

However, as the trend to distributed applications developed, an end-user programming capability was introduced under the name Transaction Processing Language (TPL).

Applications could be stored locally on floppy disk and low-priority transaction data spooled for transmission when a mainframe link was available, or at night when traffic was otherwise light.

The natural ingenuity of the 7500 series software developers resulted in the appearance in the early 1980s of highly specialised TEs such as Pac-Man and Space Invaders, for which the fast screen-handling abilities of the hardware was ideal.

How far these games spread is unknown, but as the TEs were single-function loading Space Invaders would be obvious from the cessation of the normal front-end processes.