Desk accessory
| Company type | Software module |
|---|---|
| Industry | Computing, Software |
| Founded | 1980s |
| Products | Calculator, Alarm Clock, System Preferences, Chooser, Scrapbook, Spell checkers |
A desk accessory (DA), also known as a desklet in computing, refers to a compact auxiliary or temporary application designed to operate alongside other software within a desktop environment. Early instances, such as Sidekick and Macintosh desk accessories, provided rudimentary multitasking functionality on platforms that did not support full multitasking.
Personal information managers
Initial personal information management tools like Norton Desktop and Borland's Sidekick included features such as pop-up calculators, alarms, calendars, and other utilities tailored for single-tasking systems like MS-DOS. These programs utilized terminate-and-stay-resident methods to remain accessible while other applications were running.
Apple Macintosh
With the launch of the classic Mac OS in 1984, Desk Accessories were introduced as software modules implemented as device drivers, enabling small helper applications to function concurrently with other software. This innovation allowed limited multitasking on systems lacking native multitasking support.
Operating as a specialized type of driver, DAs were loaded into the driver queue and received CPU time cooperatively when the active program invoked SystemTask(). They presented a unique window frame style to maintain a consistent user interface. Early examples included utilities like Calculator and Alarm Clock, while system tools such as System Preferences, Chooser, and Scrapbook originated as DAs. Commercial third-party DAs, including spell checkers, were also available. Although initially difficult to create due to their distinct architecture and tight memory limits (approximately 8K bytes), DA development eventually became similar in complexity to standard applications.
A specialized utility called Font/DA Mover was used to organize DA setups since these accessories resided inside the System file's 'DRVR' resources or other loaded resource files instead of being installed or launched like conventional applications. DAs embedded within particular programs could only be accessed when those programs were active, appearing on the Apple menu accordingly. Resource numbering permitted DAs to maintain a small internal "resource fork," which the mover utility managed during transfers.
Following the introduction of System 7, which incorporated standard cooperative multitasking, reliance on DAs diminished as developers favored compact standalone applications. Nevertheless, support for DAs persisted through Mac OS 9.x to maintain backward compatibility. From System 7 onward, DAs could be moved and renamed directly through the Finder like regular applications, removing the necessity for Font/DA Mover and limiting suitcases exclusively to font management. When launched, DAs executed within the Finder’s process space. Their icons typically featured a mirrored version of the application icon with the writing hand reversed.
Comparable solutions for small utility programs were also present in operating systems designed for the Apple IIGS and Apple IIe.
GEM
GEM bore a strong resemblance to the Macintosh interface, particularly in its use of desk accessories to facilitate multiple program access on systems designed to run only one full application at any given moment. Unlike the Macintosh’s cooperative multitasking approach, GEM employed task switching for its desk accessories.
From a technical standpoint, these desk accessories were actually DOS .EXE files with a .ACC (Accessory) extension instead of .APP. Each .ACC file could house several accessories; for example, the common Calculator, Clock, and Print Spooler were combined within CALCLOCK.ACC. Installation typically involved copying these .ACC files into folders like \GEMBOOT in earlier versions or \GEMAPPS\GEMSYS starting with GEM/3.
Since every accessory loaded diminished the memory available for main applications, users frequently renamed .ACC files to different extensions (such as .ACX) to deactivate them temporarily and reclaim memory. For instance, on the Amstrad PC-1512, the Snapshot accessory was distributed as SNAPSHOT.ACX and needed renaming back to .ACC before activation.
Support for desk accessories continued in ViewMAX, the file manager for DR-DOS, which preserved the Calculator and Clock tools with minimal modifications.
Palm OS
In a manner akin to Mac OS and GEM, Palm OS expanded on the desk accessory concept through third-party contributions to enable limited multitasking within a single-application environment. Palm OS desk accessories (DAs) are small applets launched by a DA launcher application or hack that listens for system events and triggers designated DAs. Numerous Palm OS launchers provide support for running these accessories.
A Palm OS DA consists of a resource database of type 'DAcc', containing a single 'code' resource #1000 that holds the binary instructions implementing the accessory's functionality. These DAs are restricted from using global or static variables but can interact with user interface APIs and may include UI resources. When executed, control is passed directly to this code resource.
Although DAs enable some multitasking capabilities, users must close them to return to the primary application. It is possible to stack one DA over another; however, this practice risks exhausting available stack space.
See also
- Helper application, referring to auxiliary tools used by web browsers