This cache is managed differently

To Oliver, the first commentator:

This is a non-volatile cache, so it's ready after being shut-off. The transfer rate from flash is not really better than a hard drive, but access is so much faster that by putting the most used bit of start-up libraries and favorite applications in flash the overall performance feels much snappier at the times when the waits are most annoying.

It's different from a traditional most-recently used cache scheme (CPU cache and filesystem RAM cache) in that once you shown a pattern of commonly used files, they'll live in flash with relatively little turn over.