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 Choosing what to overlay
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 Most code which has been generated by any of the compilers Blinker currently
 supports is overlayable, provided far calls are used. For programmers
 working in high level languages such as C, use the LARGE or HUGE memory
 models. In CA-Clipper applications all CA-Clipper code, EXTEND.LIB, and
 portions of CLIPPER.LIB are overlayable.

 It is inevitable that almost all code in overlays will execute somewhat
 slower than if it were in the root section of the program, since there is
 always some overhead involved in managing the overlay area, even though the
 overlay manager is written in assembler, and executes very quickly.

 Whether this overhead is noticeable or not is dependent on the individual
 program, but generally very small routines and/or routines that are called
 very frequently may not be the best candidates for overlaying, as the
 overhead of the overlay manager may be large in comparison to the execution
 time of the routine. Such routines are best left in the root section.

 For example, the performance of a program that draws graphics images would
 almost certainly suffer from overlaying of the setpixel() function upon
 which all graphics operations are based, since the routine would probably be
 called many thousands of times per second.

 Blinker provides several link time commands, such as BLINKER OVERLAY
 THRESHOLD and MODULE that can aid you in easily separating code that should
 be overlaid from that which should not. See chapter 9 for further details on
 these commands.