a substrate containing wiring traces for conducting signals;

a plurality of contact pads along a first edge of the substrate, the plurality of contact pads for mating with a memory module socket on a motherboard;

a plurality of memory chips mounted on the substrate for storing host data from a host on the motherboard;

a branching Advanced Memory Buffer (AMB) mounted on the substrate for buffering the host data to and from the plurality of memory chips;

uplink contact pads, in the plurality of contact pads, that carry southbound uplink frames of the host data generated by the host for writing to the plurality of memory chips or for writing to downstream memory modules, and that carry northbound uplink frames of host data read from the plurality of memory chips or read from downstream memory modules toward the host;

first downlink contact pads, in the plurality of contact pads, that carry first southbound downlink frames of the host data generated by the host for writing to a first plurality of memory chips in a first downstream memory module in a first branch, and that carry first northbound downlink frames of host data read from the first plurality of memory chips in the first downstream memory module in the first branch;

second downlink contact pads, in the plurality of contact pads, that carry second southbound downlink frames of the host data generated by the host for writing to a second plurality of memory chips in a second downstream memory module in a second branch, and that carry second northbound downlink frames of host data read from the second plurality of memory chips in the second downstream memory module in the second branch;

wherein the branching AMB connects through the wiring traces to the uplink contact pads, to the first downlink contact pads, to the second downlink contact pads, and to the plurality of memory chips;

wherein the plurality of memory chips have data lines that carry the host data and connect to the branching AMB but are isolated from the uplink contact pads, from the first downlink contact pads, and from the second downlink contact pads by the branching AMB;

a replicator, in the branching AMB, for copying the southbound uplink frames received from the uplink contact pads to the first downlink contact pads to generate the first southbound downlink frames, and for copying the southbound uplink frames received from the uplink contact pads to the second downlink contact pads to generate the second southbound downlink frames; and

a stream combiner, in the branching AMB, for transferring the first northbound downlink frames received from the first downlink contact pads to the uplink contact pads to generate the northbound uplink frames, and for transferring the second northbound downlink frames received from the second downlink contact pads to the uplink contact pads to generate the northbound uplink frames,

whereby the branching fully-buffered memory module replicates southbound uplink frames to generate both the first southbound downlink frames to the first branch of the first downstream memory module and the second southbound downlink frames to the second branch of the second downstream memory module.