Non-uniform memory access

They were developed commercially during the 1990s by Unisys, Convex Computer (later Hewlett-Packard), Honeywell Information Systems Italy (HISI) (later Groupe Bull), Silicon Graphics (later Silicon Graphics International), Sequent Computer Systems (later IBM), Data General (later EMC, now Dell Technologies), Digital (later Compaq, then HP, now HPE) and ICL.

the Symmetrical Multi Processing XPS-100 family of servers, designed by Dan Gielan of VAST Corporation for Honeywell Information Systems Italy.

Many supercomputer designs of the 1980s and 1990s focused on providing high-speed memory access as opposed to faster processors, allowing the computers to work on large data sets at speeds other systems could not approach.

To handle these cases, NUMA systems include additional hardware or software to move data between memory banks.

This operation slows the processors attached to those banks, so the overall speed increase due to NUMA heavily depends on the nature of the running tasks.

For this reason, ccNUMA may perform poorly when multiple processors attempt to access the same memory area in rapid succession.

[2] Since NUMA largely influences memory access performance, certain software optimizations are needed to allow scheduling threads and processes close to their in-memory data.

Examples of ccNUMA-enabled chipsets are the SGI Shub (Super hub), the Intel E8870, the HP sx2000 (used in the Integrity and Superdome servers), and those found in NEC Itanium-based systems.

The motherboard of an HP Z820 workstation with two CPU sockets, each with their own set of eight DIMM slots surrounding the socket.
One possible architecture of a NUMA system. The processors connect to the bus or crossbar by connections of varying thickness/number. This shows that different CPUs have different access priorities to memory based on their relative location.
Topology of a ccNUMA Bulldozer server extracted using hwloc's lstopo tool.