XMODEM-1K is an xmodem/crc protocol that uses 1024 (1K) data blocks instad of 128. For most transmissions, the use of this protocol reduces transmission time in comparison to the use of normal XMODEM. The transmission time is reduced because of the large block size reduces both the number of line turnarounds and the number of times the transmitting device must wait for a responce before sending the next block or retransmitting the previously sent block.