The compression/decompression scheme allows the Personal LaserWriter LS to
image documents that would not normally fit in 512K of RAM. The amount of
compression depends on the image, and is not really predictable. Apple's
testing showed that the only pages that could not fit in the standard RAM
(U.S. Letter paper) were graphics containing patterns that don't lend
themselves to effective compression. It was somewhat easier to overflow
RAM when printing on legal sized paper.
With the additional RAM installed (making the total 1MB), Testing was
unable to find a document that the printer would not image.