shebanow@ernie.berkeley.edu (Mike Shebanow) (04/24/86)
References: (Beware the line eater) All this talk about the necessity of setting the cache bit in order to have the cache bit working has made me wonder. So I did a few tests, and, as far as I can determine, setting the cache bit makes little or no difference in startup times. Using a 512K Mac with the new ROMs and an HD20, the times to launch MacWrite (128K cache) were: 1st Launch 2nd Launch Subsequent Launches Cache bit off: 13.3 secs 9.4 secs 8.9 secs Cache bit on: 13.2 secs 9.3 secs 8.9 secs Given my timing methods (stopwatch with clumsy fingers), these figures are pretty much identical. Some studying of "Tech Note #57: Macintosh Plus Overview" leads me to believe that the cache bit is actually used for "supercharging" applications. In the Resource Manager section of TN57, it says: "There is a new 'supercharging' capability which allows specially formatted applications to start up faster due to mass disk reads. It also uses various caching techniques to minimize disk access. Apple will provide information on 'supercharging' application resource files in the future." I believe that setting the cache bit tells the Resource Manager (or the Segment Loader??) that the application has been supercharged. It would be nice if someone from Apple (Mr. Rosenstein?) could confirm this theory. Andrew Shebanow shebanow@ernie.BERKELEY.EDU