Administration > Environment Variables > APTBITMAPK — Specifying Maximum Memory for Screen Display of Graphics
  
APTBITMAPK — Specifying Maximum Memory for Screen Display of Graphics
Specifies the maximum amount of memory used for screen display of graphics. The default is 64,000 kilobytes. When a request is made to display a graphic that would cause the limit to be exceeded, the least recently referenced image is released to create space to accommodate the current graphic. For example,
set APTBITMAPK 9000
sets the maximum amount of memory to 9 megabytes.