Data transfer, or file, protocols are methods by which computers send binary files via modem. There are several protocols in use, such as Xmodem and Zmodem. Xmodem, developed by Ward Christensen, sends data in 128-byte blocks. A checksum is attached to each of these blocks. The receiving modem checks this checksum to make sure the data traveled uncorrupted. If the data has been damaged, it is resent. In addition, Xmodem/CRC adds a Cyclical Redundancy Check algorithm to further this error correction. Xmodem is a relatively slow protocol, so should only be used when no others are available.
Zmodem, developed by Chuck Forsberg, ends data blocks with CRC-32 error checking. It does not wait, however, for a message from the receiving computer. It simply assumes that everything is OK. This "streaming" makes Zmodem faster than many other protocols. Zmodem is also capable of multiple file transfer and crash recovery, in which a transfer can resume after it has been aborted.
Zmodem, developed by Chuck Forsberg, ends data blocks with CRC-32 error checking. It does not wait, however, for a message from the receiving computer. It simply assumes that everything is OK. This "streaming" makes Zmodem faster than many other protocols. Zmodem is also capable of multiple file transfer and crash recovery, in which a transfer can resume after it has been aborted.
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