|
Uniform: All processors take the same time to reach all memory locations.
|
Nonuniform (NUMA): Memory access is not uniform so that it takes a different time to get data by a given processor from each memory bank. This is natural for distributed memory machines but also true in most modern shared memory machines
-
DASH (Hennessey at Stanford) is best known example of such a virtual shared memory machine which is logically shared but physically distributed.
-
ALEWIFE from MIT is a similar project
-
TERA (from Burton Smith) is Uniform memory access and logically shared memory machine
|
Most NUMA machines these days have two memory access times
-
Local memory (divided in registers caches etc) and
-
Nonlocal memory with little or no difference in access time for different nonlocal memories
|
|
This simple two level memory access model gets more complicated in proposed 10 year out "petaflop" designs
|
