Methods and apparatus of stacking DRAMs

1. A memory device for electrical connection to a memory bus, the memory device comprising:

a plurality of dynamic random access memory (“DRAM”) integrated circuits, stacked in a vertical direction, each DRAM integrated circuit comprising a memory core of a plurality of cells and accessible at a first speed; and

an interface integrated circuit electrically coupled to the plurality of DRAM integrated circuits for providing an interface between the DRAM integrated circuits and the memory bus at a speed greater than the first speed;

wherein the interface integrated circuit is adapted for providing a predetermined electrical load on the memory bus independent of a number of the DRAM integrated circuits to which the interface integrated circuit is electrically coupled.

2. The memory device as set forth in claim 1 , wherein:

each DRAM integrated circuit comprises a DRAM integrated circuit die.

3. The memory device as set forth in claim 1 , wherein:

the plurality of DRAM integrated circuits comprises a DRAM integrated circuit package.

4. The memory device as set forth in claim 1 , wherein:

the interface integrated circuit is adapted to operate in accordance with an industry defined specification.

5. The memory device as set forth in claim 1 , wherein:

the interface integrated circuit is adapted to operate in accordance with a DDR2 SRAM specification.

6. A memory device for electrical connection to a memory bus, the memory device comprising:

a plurality of dynamic random access memory (“DRAM”) integrated circuits, stacked in a vertical direction, each DRAM integrated circuit comprisina a memory core of a plurality of cells and accessible at a first speed; and

an interface integrated circuit electrically coupled to the plurality of DRAM integrated circuits for providing an interface between the DRAM integrated circuits and the memory bus at a speed greater than the first speed;

wherein the plurality of DRAM integrated circuits comprise:

a working pool of “p” DRAM integrated circuits; and

a spare pool of “q” DRAM integrated circuits;

wherein “p” and “q” comprise integer values.

7. The memory device as set forth in claim 6 , further comprising:

a memory controller, coupled to at least one of the interface integrated circuit and the plurality of DRAM integrated circuits, for detecting occurrence of a pre-defined number of errors in working memory integrated circuits and for signaling to the interface integrated circuit to indicate the occurrence of the pre-defined number of errors; and

wherein the interface integrated circuit is adapted to replace at least one DRAM integrated circuit of the working pool with at least one DRAM integrated circuit of the spare pool.

8. The memory device as set forth in claim 7 , wherein:

the memory controller is further adapted to signal the occurrence of the pre-defined number of errors using in-band signaling.

9. The memory device as set forth in claim 7 , wherein:

the memory controller is further adapted to signal the occurrence of the pre-defined number of errors using side band signaling.

10. A memory device for electrical connection to a memory bus, the memory device comprising:

a plurality of dynamic random access memory (“DRAM”) integrated circuits, stacked in a vertical direction, each DRAM integrated circuit comprising a memory core of a plurality of cells and accessible at a first speed; and

an interface integrated circuit electrically coupled to the plurality of DRAM integrated circuits for providing an interface between the DRAM integrated circuits and the memory bus at a speed greater than the first speed;

wherein the plurality of DRAM integrated circuits comprise:

a working pool of “p” DRAM integrated circuits; and

a mirrored pool of “q” DRAM integrated circuits;

wherein “p” and “q” comprise integer values.

11. The memory device as set forth in claim 10 , further comprising:

a memory controller, coupled to at least one of the interface integrated circuit and the plurality of DRAM integrated circuits, for detecting occurrence of a pre-defined number of errors in working memory integrated circuits and for signaling to the interface integrated circuit to indicate the occurrence of the pre-defined number of errors; and

wherein the interface integrated circuit is adapted to replace at least one DRAM integrated circuit of the working pool with at least one DRAM integrated circuit of the mirrored pool.

12. The memory device as set forth in claim 11 , wherein:

the memory controller is further adapted to signal the occurrence of the pre-defined number of errors using in-band signaling.

13. The memory device as set forth in claim 11 , wherein:

the memory controller is further adapted to signal the occurrence of the pre-defined number of errors using side band signaling.

14. The memory device as set forth in claim 10 , wherein:

“p” equals “q”.

15. A memory device for electrical connection to a memory bus, the memory device comprising:

a plurality of dynamic random access memory (“DRAM”) integrated circuits, stacked in a vertical direction, each DRAM integrated circuit comprising a memory core of a plurality of cells and accessible at a first speed;

an interface integrated circuit electrically coupled to the plurality of DRAM integrated circuits for providing an interface between the DRAM integrated circuits and the memory bus at a speed greater than the first speed; and

a memory scheme wherein the plurality of DRAM integrated circuits comprise;

“p” DRAM integrated circuits used as a working memory device for storing data across the “p” DRAM integrated circuits; and

at least one additional DRAM integrated circuit for storing additional information for the data stored in the “p” DRAM integrated circuits;

wherein “p” comprises an integer value.

16. The memory device as set forth in claim 15 , wherein:

the memory scheme comprises a RAID memory scheme; and

the additional information comprises parity information.

17. The memory device as set forth in claim 15 , wherein:

the additional information comprises prefetch information.

18. A memory device for electrical connection to a memory bus, the memory device comprising:

a plurality of dynamic random access memory (“DRAM”) integrated circuits, stacked in a vertical direction, each DRAM integrated circuit comprising a memory core of a plurality of cells and accessible at a first speed;

an interface integrated circuit electrically coupled to the plurality of DRAM integrated circuits for providing an interface between the DRAM integrated circuits and the memory bus at a speed greater than the first speed; and

a socket, coupled to the stacked plurality of DRAM integrated circuits, for adding at least one additional DRAM integrated circuit to the stacked plurality of DRAM integrated circuits.

19. The memory device as set forth in claim 18 , wherein:

the interface integrated circuit is stacked with the plurality of DRAM integrated circuits.

20. A memory device for electrical connection to a memory bus, the memory device comprising:

a plurality of dynamic random access memory (“DRAM”) integrated circuits, stacked in a vertical direction, each DRAM integrated circuit comprising a memory core of a plurality of cells and accessible at a first speed; and

an interface integrated circuit electrically coupled to the plurality of DRAM integrated circuits for providing an interface between the DRAM integrated circuits and the memory bus at a speed greater than the first speed;

wherein the plurality of DRAM integrated circuits includes:

at least one DRAM integrated circuit which was incorporated into the memory device at manufacturing time; and

at least one DRAM integrated circuit which was incorporated into the memory device at a later time.

21. A memory device for electrical connection to a memory bus, the memory device comprising:

a plurality of dynamic random access memory (“DRAM”) integrated circuits, stacked in a vertical direction, each DRAM integrated circuit comprising a memory core of a plurality of cells and accessible at a first speed;

an interface integrated circuit electrically coupled to the plurality of DRAM integrated circuits for providing an interface between the DRAM integrated circuits and the memory bus at a speed greater than the first speed;

a printed circuit board; and

a socket for mounting the plurality of DRAM integrated circuits in a rank to the printed circuit board.

22. A memory device for use with a memory bus, the memory bus comprising:

a plurality of dynamic random access memory (“DRAM”) integrated circuits, stacked in a vertical direction, each comprising a memory core of a plurality of cells accessible at low speed; and

an interface integrated circuit for providing an interface, at a high speed relative to the low speed, between the DRAM integrated circuits and the memory bus;

wherein the interface integrated circuit is adapted for providing a predetermined electrical load on the memory bus independent of a number of the DRAM integrated circuits to which the interface integrated circuit is electrically coupled.

23. A memory device for use with a memory bus, the memory bus comprising:

means for stacking, in a vertical direction, a plurality of dynamic random access memory (“DRAM”) integrated circuits each comprising a memory core of a plurality of cells accessible at a first speed; and

means for providing an interface between the DRAM integrated circuits and the memory bus at a speed greater than the first speed;

wherein the means for providing the interface is adapted for providing a predetermined electrical load on the memory bus independent of a number of the DRAM integrated circuits to which the means for providing the interface is electrically coupled.