About a day is ~90 microseconds, which is really fast, even for an SSD. The FusionIO folks claim they can do 30 microseconds though, which is really incredible, just a couple hundred times slower than ram.
I wanted to say that that was within an order of magnitude to the cost of a simple system call, but it looks like system calls are much much faster than my intuition suggested[1], and they're in the range of RAM access.
Looking at a random (2010) SSD review, it lists average read access times of less than 0.15 milliseconds = 150 microseconds for all of the SSDs involved. The long standing "gold standard" Intel X25-M had 70 μs.
