1. A re-configurable bus system comprising: a host interface to a host;
a physical-layer switch;
primary lanes between the host interface and the physical-layer switch;
an extra lane between the host interface and the physical-layer switch;
wherein each of the primary lane and the extra lane is a bi-directional serial bus;
a first slot for receiving a first peripheral device;
a second slot for receiving a second peripheral device;
first lanes between the physical-layer switch and the first slot; and
second lanes between the physical-layer switch and the second slot;
wherein the physical-layer switch can be configured into a first maximum configuration wherein the primary lanes connect to the first lanes to the first slot, while the extra lane connects to the second slot;
wherein the physical-layer switch can be configured into a partitioned configuration wherein the primary lanes are partitioned among the first and second slot and the extra lane is not connected to either the first slot or to the second slot;
wherein the primary lanes comprise 2N lanes, wherein N is a whole number of 2 or more;
wherein the extra lane comprises exactly one lane;
whereby a total number of lanes from the host is exactly 2N+1 lanes.
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