Hands-On System Programming with Linux

How fast is fast?

In Chapter 2, Virtual Memory, in the section on the memory pyramid, we saw Table 2: Memory Hierarchy Numbers. Here, a representative look at the numbers was done—the typical access speeds for different kinds of memory technologies (for both the embedded and server space) are enumerated in the table.

A quick recap gives us the following in terms of typical memory (and network) access speeds. Of course, these numbers are only indicative, and the very latest hardware might well have superior performance characteristics; here, the concept is what's being focused upon:

CPU registers	CPU caches	RAM	Flash	Disk	Network roundtrip
300 - 500 ps	0.5 ns (L1) to 20 ns (L3)	50–100 ns	25–50 us	5–10 ms	>= 100s of ms

Table 3 : Hardware ...