I know OS X has had a feature for compressing data in RAM on the fly—the processor is much faster than RAM, so compressing & uncompressing & loading a smaller a

I know OS X has had a feature for compressing data in RAM on the fly—the processor is much faster than RAM, so compressing & uncompressing & loading a smaller amount of data was faster than just loading the larger amount of uncompressed data. That might be what you're seeing.