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When the REVMEDIA file for a particular location is attached, two critical pieces of information are stored in a special record with the key of %%REVMEDIA%%.  This record can be edited with the System Editor, as shown below:

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Field 1 is the filename assigned to the next file to be created.  In this case REV59011.LK and REV59011.OV will be assigned to the next linear hash file.  (If a dictionary is also created, the data will be stored in REV59012.OK and REV59012.OV.)

Field 2 is the volume identifier, set by the NAME_VOLUME subroutine.

Media Updates and the Media Handle

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The media handle is created by the OPEN.MEDIA call. If successful, this call returns a handle that is used in subsequent media access calls such as READ.MEDIA and WRITE.MEDIA.  As with the file handle created by OPEN.FILE, the media handle is stored by the system. The handle returned by OPEN.MEDIA is kept in the SYSVOLUMES file as field five.

MFS Access to Media Calls

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For these calls, information passed in the HANDLE argument is the handle of the media map. This handle is used in virtually the same manner as a file handle.