Memory chip for high capacity memory subsystem supporting multiple speed bus

1. A first memory module, comprising:

a plurality of addressable storage locations for storing data;

a first interface for receiving memory access commands for accessing said addressable storage locations;

a second interface for re-transmitting memory access commands received in said first interface;

control logic which supports a plurality of modes of operation, including a first mode and a second mode;

wherein, in said first mode of operation, a first portion of said first interface receives a first portion of each memory access command at a first bus frequency, and a second portion of said first interface receives a second portion of each memory access command at a second bus frequency, said first bus frequency being different from said second bus frequency, and re-transmits at least a portion of said first portion of at least some said memory access commands at said first bus frequency using said second interface, and re-transmits at least a portion of said second portion of said at least some said memory access commands at said second bus frequency using said second interface to a second memory module; and

wherein, in said second mode of operation, said first interface receives each memory access command at a single bus frequency, and in response thereto said control logic determines, with respect to each said memory access command received by said first interface, whether the respective memory access command addresses a data storage location in said first memory module, and (a) accesses a corresponding data storage location in said first memory module if the respective memory access command addresses a data storage location in said first memory module, and (b) re-transmits the respective memory access command at said single bus frequency to a second memory module if the respective memory access command does not address a data storage location in said first memory module.

2. The first memory module of claim 1 , wherein, in said second mode of operation, said first memory module is for use in a daisy-chained configuration of memory modules, in which a first set of I/O ports is for receiving outbound data from one of an access control module controlling access to a daisy-chain of memory modules, said daisy chain including said first memory module, and a previous memory module in said daisy-chain of memory modules, a second set of I/O ports is for re-transmitting outbound data received in said first set of I/O ports to a next memory module in said daisy-chain of memory modules, a third set of I/O ports is for receiving inbound data from said next memory module in said daisy-chain of memory modules, and a fourth set of I/O ports is for re-transmitting inbound data received in said third set of I/O ports and for transmitting inbound data originating in said first memory module to one of said access control module and said previous memory module in said daisy chain of memory modules, said first set having the same number of ports as said second set, said third set having the same number of ports as said fourth set.

3. The first memory module of claim 1 , wherein, in said first mode of operation, each said memory access command received by said first interface accesses addressable storage locations in a set of memory modules, said set containing a plurality of memory modules, said set including said first memory module and said second memory module.

4. The first memory module of claim 1 , wherein said first bus frequency is L times said second bus frequency, where L is an integer.

5. The first memory module of claim 4 ,

wherein, in said first mode of operation, said first portion of said first interface receives said first portion of each memory access command in each of N successive bus cycles, where N is greater than one;

wherein, in said second mode of operation, said second portion of said first interface receives said second portion of each said memory access command in each of M successive bus cycles, where M is at least one; and

wherein N=M×L.

6. The first memory module of claim 1 , wherein said first and second bus frequencies are derived by said first memory module from a common external clock signal, said external clock signal being divided by an integer N to obtain said first bus frequency and by an integer M to obtain said second bus frequency, where N is greater than or equal to one, and M is greater than N.

7. The first memory module of claim 1 , wherein said single bus frequency of said second mode of operation is equal to said first bus frequency of said first mode of operation, said first bus frequency being greater than said second bus frequency.

8. The first memory module of claim 1 , wherein in said first mode of operation said memory access commands comprise memory write commands, said first portion including command/address data and said second portion including data to be written to storage locations in at least one memory module including said first memory module, said first bus frequency being higher than said second bus frequency.

9. The first memory module of claim 8 , wherein in said first mode of operation, at least one I/O port of said first memory module is used for transmitting data read from storage locations in said first memory module to an access control module responsive to said data access commands, said at least one I/O port transmitting data at said second bus frequency.

10. The first memory module of claim 1 ,

wherein said first interface is for coupling to a point-to-point communications link connecting said first memory module with a device from which said memory access communications are received; and.

wherein said second interface is for coupling to a point-to-point communications link connecting said first memory module with said second memory module.