1. A method of writing data to a memory subsystem in a computer system, wherein the data is supplied by an input/output (I/O) bus, and wherein the I/O bus provides a STROBE signal, an occurrence of the STROBE signal being indicative of a time when an I/O data word on the I/O bus is valid, the method comprising: storing a first I/O data word, provided by the I/O bus after a first occurrence of the STROBE signal, in data buffer means; retrieving a memory data word from the memory subsystem in response to the first occurrence of the STROBE signal; storing a second I/O data word, provided by the I/O bus after a second occurrence of the STROBE signal, in the data buffer means; modifying the memory data word with the first and second I/O data words to form a modified data word; generating error correction code (ECC) data corresponding to the modified data word; and writing the modified data word and the ECC data to the memory subsystem.