BLINKER OVERLAY UMB           Enable use of XMS UMBs for overlays
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 Purpose  : Enable use of the XMS UMBs for overlays

 Syntax   : BLINKER OVERLAY UMB ON | OFF

 Default  : ON

 Example  : # Do not use XMS UMB's for the overlay area
            BLINKER OVERLAY UMB OFF

 This command used in conjunction with a suitable XMS driver allows the
 Blinker overlay manager to execute overlays in upper memory blocks above
 640kb. Blinker's use of UMBs is dependent on there being a suitably large
 contiguous block available. The size of the UMB allocated will be the same
 as the program's overlay opsize.

 Use of this command requires a 386 processor (or better), and an XMS 2.0
 extended memory driver that supports UMB's (upper memory blocks). UMB's are
 blocks of memory which are mapped into the area above 640kb, using the
 memory management capabilities of the 386/486 family of processors. Upper
 memory blocks are sometimes referred to as 'high memory' or LOADHI areas.

 If your XMS driver supports the loading of drivers into high memory, it is
 likely that you can use this feature. Blinker will need a UMB at least as
 large as the overlay area, so you may need to alter the placement of your
 programs in high memory to facilitate this. Most 386 memory managers provide
 utilities to help optimize this area. If both this command and the PAGEFRAME
 command are used, and both the pageframe and a UMB are available, then
 Blinker will use the pageframe.

 If either or both of these are specified and are not available on the end
 user's system, Blinker will automatically ignore these commands and allocate
 the overlay area from conventional memory. This use of UMB's may be adjusted
 at runtime through the use of the BLINKER environment variable (see the
 'Environment Variable' section in Chapter 2).

 Notes for CA-Clipper Summer '87:

 This command is only effective when the fixed overlay allocation method is
 selected with the command BLINKER OVERLAY FIXED.