As a noun memory
is (uncountable) the ability of an organism to record information about things or events with the facility of recalling them later at will.
As an adjective undecidable is
(mathematics|computing theory) incapable of being algorithmically decided in finite time for example, a set of strings is undecidable if it is impossible to program a computer (even one with infinite memory) to determine whether or not specified strings are included.