c93e1e46_Idle_Time___2010___January__Mac_OS_X
[iPhone] Accessing any file in flash memory is as quick as accessing any other file (random access). [Mac OS X] 
Disks are not so predictable: Accessing one file and then another can incur milliseconds of seek time. Doing this repeatedly for dozens or hundreds of files (possibly in multiple Finder windows at different scroll positions) may cause the disk to thrash. You can hope that the OS can put the requests into a favorable order, but you can’t rely on it, and there’s only so much it can do.
Idle Time » 2010 » January
Mac OS X