AmigaDOS Device Input and Output

AmigaDOS uses handlers and filesystems to provide a standard method of interaction with physical I/O devices. Handlers and filesystems are similar; handlers are a subset of a filesystem, supporting only a few I/O operations, while filesystems include additional support for file operations as well as directory-type operations. Handlers and filesystems reside either in ROM or in the L: directory.

Handlers and filesystems are often referred to as "AmigaDOS devices" but keep in mind that an AmigaDOS device is different from an Exec device. AmigaDOS devices appear as names within the DOS name space, for example, SER:, RAM: or DF0: (rather than Exec's serial.device or trackdisk.device). AmigaDOS devices are often built on top of Exec devices using the Exec device to perform the low-level functions.

Examples of this type include:

• The Port-handler (SER:, PAR:, and PRT:) which is built on top of the serial.device, parallel.device, and printer.device.
• The filesystem (DF0:, DF1:) which is built on top of the trackdisk.device.
• CON: (console handler) which is built on top of the console.device.

It is not required for a handler or filesystem to be built on top of an Exec device. In some cases the handler manages its own resources. For example, for the RAM-handler the resource being maintained is RAM. While the memory used by the RAM-handler is still allocated by Exec, there is really no underlying Exec device.

Note that, unlike an Exec device, each handler and filesystem executing must have its own process.