Editing XMODEM (section)

===XMODEM-1K===
Another way to solve the throughput problem is to increase the packet size. Although the fundamental problem of latency remains, the speed at which it becomes a problem is higher. XMODEM-1K with 1024-byte packets{{r|meeks198902}} was the most popular such solution. In this case, the throughput at 9600&nbsp;bit/s is 81%, given the same assumptions as above.

XMODEM-1K was an expanded version of XMODEM-CRC, which indicated the longer block size in the ''sender'' by starting a packet with the <kbd><STX></kbd> character instead of <kbd><SOH></kbd>. Like other backward-compatible XMODEM extensions, it was intended that a -1K transfer could be started with any implementation of XMODEM on the other end, backing off features as required.

XMODEM-1K was originally one of the many improvements to XMODEM introduced by [[Chuck Forsberg]] in his [[YMODEM]] protocol. Forsberg suggested that the various improvements were optional, expecting software authors to implement as many of them as possible. Instead, they generally implemented the bare minimum, leading to a profusion of semi-compatible implementations, and eventually, the splitting out of the name "YMODEM" into "XMODEM-1K" and a variety of YMODEMs. Thus XMODEM-1K actually post-dates YMODEM, but remained fairly common anyway.