The main virtue for using single Bus structure is

CONCEPT: A single-bus structure connects the processor, main memory and all I/O devices to one common set of shared wires (the system bus). The defining trade-off of this design is simplicity and economy versus throughput: because every transfer shares the same path, the structure is cheap and uniform to build, but only one device pair can use the bus at any instant.

Two consequences follow directly from this single shared path:

• Economy of wiring: a single set of address, data and control lines serves the whole machine, so far less cabling/interconnect is needed than in a multi-bus design — this keeps cost low.

• Uniform attachment: every device talks over the same standard interface, so a new peripheral is added simply by connecting it to the common bus, without redesigning dedicated links — expansion is easy.

APPLICATION: Therefore the principal virtue of a single-bus structure is its low cost together with the ease of attaching peripheral devices to a common, standard interface.

CONTRAST: Speed is NOT a virtue of this design — the shared bus is the classic bottleneck (only one transfer at a time), so any option built on fast transfer or speed mis-states the trade-off; and naming only price is too narrow because it omits the modular, easy-expansion benefit that is the other half of the answer.

Note: this item refers to the single (system) bus inside a computer's organization, not to a LAN 'bus topology'; do not apply network-collision reasoning here.