Desk accessory

Early personal information managers, such as Norton Desktop and Borland's Sidekick, provided pop-up calculator, alarm, calendar and other functions for single-tasking operating systems like MS-DOS using terminate-and-stay-resident techniques.

Introduced in 1984 as part of the operating system for the Apple Macintosh computer, a Desk Accessory (DA) was a piece of software written as a device driver, conforming to a particular programming model.

It was installed in the driver queue, and given time periodically and co-operatively as a result of the host application calling SystemTask() within its main loop.

[1] However, since on the early Mac OS drivers did not have any special privileges, writing a DA was, with practice, no more difficult than any other application.

Under System 7 and later, DAs could be moved and renamed using the Finder like normal applications, removing the need for Font/DA Mover and confining suitcases to font management.

Since each desk accessory loaded reduced the amount of memory available for programs, one technique for temporarily increasing available space was to rename one or more .ACC files to have a different suffix (usually .ACX) and restart GEM.

Desk accessories continued to be supported in ViewMAX, the DR-DOS file manager, which was supplied with almost unchanged versions of Calculator and Clock.

The DA launcher may watch for keystrokes or other system events and pop up a predefined desk accessory.

However, unlike in Mac OS and GEM, after the user is done working with the DA, it must be closed to return to the underlying application.