Memory system topology

1. A memory system comprising:

a memory controller; and

a plurality of memory modules including a first memory module and an Nth memory module, wherein each of the first through (N−1)th memory module is coupled to receive data from a same subsequent memory module via both an upstream link and a downstream link;

wherein the memory controller is directly coupled to the Nth memory module by a downstream link and is directly coupled to the first memory module by an upstream link;

wherein information sent from the memory controller to a particular memory module of said plurality of memory modules is conveyed directly to the Nth memory module through a downstream link and, as necessary, through additional downstream links to the particular memory module.

2. The memory system as recited in claim 1 , wherein information conveyed from a given memory module of said plurality of memory modules to the memory controller is conveyed from the given memory module through upstream links to the memory controller.

3. The memory system as recited in claim 2 , wherein each of the plurality of memory modules includes a buffer configured to buffer addresses, commands, and data.

4. The memory system as recited in claim 3 , wherein each of the plurality of memory modules comprise a fully buffered dual inline memory module (FB-DIMM).

5. The memory system as recited in claim 3 , wherein the plurality of memory modules are physically arranged as a single row of memory modules, wherein the first memory module is closest to the memory controller, and subsequent memory modules of the plurality of memory modules are increasingly further from the memory controller.

6. The memory system as recited in claim 3 , wherein the plurality of memory modules are physically arranged as a single row of memory modules, and wherein the Nth memory module is closest to the memory controller.

7. The memory system as recited in claim 6 , wherein the first memory module is second closest to the memory controller, and the (N−1)th memory module is third closest to the memory controller.

8. The memory system as recited in claim 3 , wherein the plurality of memory modules are physically arranged as two rows of memory modules, wherein the first memory module and the Nth memory module are closest to the memory controller and are approximately equidistant from the memory controller.

9. The memory system as recited in claim 3 , wherein read data is returned in an order in which it was requested by the memory controller.

10. The memory system as recited in claim 9 , wherein upstream communication takes place by sending a pipelined sequence of fixed-size frames on upstream links, and wherein a memory module may update a content of a frame prior to forwarding the frame.

11. The memory system as recited in claim 3 , wherein all commands and write data are conveyed via downstream links, and wherein all read data is conveyed via upstream links.

12. A method comprising:

conveying information via a downstream link from a memory controller directly to an Nth memory module of a plurality of memory modules including a first memory module and the Nth memory module, wherein each of the first through (N−1)th memory module is coupled to receive data from a same subsequent memory module via both an upstream link and a downstream link; and

receiving information via an upstream link at the memory controller directly from the first memory module of the plurality of memory modules.

13. The method as recited in claim 12 , further comprising conveying information from a memory module of said plurality of memory modules to the memory controller by sending a pipelined sequence of fixed-size frames via upstream links.

14. The method as recited in claim 13 , further comprising a memory module of the plurality of memory modules updating a content of a frame received via an upstream link prior to forwarding the frame via an upstream link.

15. The method as recited in claim 13 , wherein each of the plurality of memory modules comprise a fully buffered dual inline memory module (FB-DIMM).

16. A computing system comprising:

a processor;

a plurality of memory modules including a first memory module and an Nth memory module, wherein each of the first through (N−1)th memory module is coupled to receive data from a same subsequent memory module via both an upstream link and a downstream link; and

a memory controller coupled to the processor and the memory modules, wherein the memory controller is directly coupled to the Nth memory module by a downstream link and is directly coupled to the first memory module by an upstream link, and wherein information sent from the memory controller to a particular memory module of said plurality of memory modules is conveyed directly to the Nth memory module through a downstream link and, as necessary, through additional downstream links to the particular memory module.

17. The computing system as recited in claim 16 , wherein information conveyed from a given memory module of said plurality of memory modules to the memory controller is conveyed from the given memory module through upstream links to the memory controller.

18. The memory system as recited in claim 17 , wherein each of the plurality of memory modules comprise a fully buffered dual inline memory module (FB-DIMM).

19. The memory system as recited in claim 17 , wherein the plurality of memory modules are physically arranged as a single row of memory modules, wherein the first memory module is closest to the memory controller.

20. The memory system as recited in claim 17 , wherein the plurality of memory modules are physically arranged as a single row of memory modules, and wherein the Nth memory module is closest to the memory controller.