The packet format consisted of a 6-byte header and then between zero and 4096 bytes in the payload. The packet starts with a single \020 (control-P). This is followed by a single byte, known as "K", containing a value of 1 to 8 indicating a packet size from 32 to 4096 bytes, or a 9 indicating a control packet. Many systems only supported K=2, meaning 64 bytes. The next two bytes were a 16-bit checksum of the payload, not including the header. The next byte is the data type and finally, the last byte is the XOR of the header, allowing it to be checked separately from the payload.