Using CitectSCADA > Communicating with I/O Devices > Using a Disk I/O Device

Using a Disk I/O Device

In addition to connecting to actual I/O devices, CitectSCADA supports the configuration of disk I/O devices, which exist only within your computer. The value of each variable in the disk I/O device is stored on your computer's hard disk.

Note: With the release of V7.20, a feature called persistence can be applied to I/O devices in memory mode. Using a Persisted Memory I/O device is recommended as an alternative to using a disk I/O device, as full synchronization is supported if a server becomes unavailable for a period of time. See Persisted I/O Memory Modefor more information.

Once configured, disk I/O devices appear exactly as any other I/O device in your system, but are not connected to any field equipment. Disk I/O devices can contain any type of variable supported by CitectSCADA, and you can configure them to emulate any supported I/O device. You can also specify a generic protocol for a disk I/O device.

A disk I/O device is useful when the status of your plant needs to be restored after a planned or unplanned system shutdown. You can configure your system to continually update a disk I/O device with the subset of variables that defines the status of your plant. When you restart your system after a shutdown, CitectSCADA can restore this status immediately.

You can also use disk I/O devices for storing predefined data that needs to be recalled immediately when a process is necessary (for example, in a simple recipe system).

Note: If you create a RAM disk in the computer for the disk I/O device, you do not need to create or copy the disk file to the RAM disk. CitectSCADA automatically creates a disk file on startup. Do not set up your Disk I/O device on a RAM disk if you want the data written to it to survive a power cycle of the Servers.

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