A data packer of an input/output hub of a computer system packs and formats write data that is supplied to it before the write data is written into a memory unit of the computer system. More particularly, the data packer accumulates write data received from lower bandwidth clients for delivery to a high bandwidth memory interface. Also, the data packer aligns the write data, so that when the write data is read out from the write data packer, no further alignment is needed.