Abstract: A test computer has a direct memory access module, interface units, and a data select unit for each of several system busses. Only some of the data on each system buss is to be transferred to the direct memory access module. The data is organized with a command or header word which may be followed by a number of data words. The principle is to first check the command word to see if any data items are desired from the particular transfer, and if they are to check the position of each data item to see if it is desired. The data select unit includes a select memory, a position counter, and a position memory. During a load mode information from the test computer is loaded into the memories and counter to designate what data is to be transferred from the system buss.