title: Virtual memory
taxon: Concept
parent: operating-systems
math: yes

Every process sees its own address space. The MMU translates each
virtual address to a physical one through page tables, and a TLB caches
the recent translations so most accesses never walk the tables.

With a TLB hit rate $h$, a TLB lookup time $t$ and a memory access time
$m$, the effective access time for a two level table is

$$
T = h(t + m) + (1 - h)(t + 3m)
$$

which is why the hit rate matters so much more than the lookup time.
See also [[eigenvalues|the eigenvalue tree]] for how trees in other
courses are linked the same way.