ZMODEM-90 can be tailored to quote only those characters the network actually eats, as opposed to every possible one. A similar improvement allows ZMODEM-90 to work on 7-bit networks, whereas earlier protocols (with the notable exception of Kermit) had all demanded 8-bits to one degree or another. Finally, ZMODEM-90 includes a basic run-length encoding compression system to further improve performance on uncompressed files. Limitations Some of the ZMODEM packets (e.g. ZACK, ZRPOS) embed a byte-offset within the transferred file as a 32-bit unsigned integer. This design limits the feasibility of ZMODEM to only reliably transfer files that are under 4GB in size. Even though the protocol could permit it, the reference (l)rzsz implementation cannot encode arbitrary non-control characters (e.g. '~') which are often used by TCP/IP connection programs like telnet and ssh as client-side "terminal escape" characters. Users must disable the terminal escape feature to achieve reliable transfers over these kinds of links, e.g. ssh -e none user@hostname. References The ZMODEM Inter Application File Transfer Protocol Synchronet External X/Y/Zmodem (SEXYZ) File Transfer Protocol Driver External links Evolution and Selection of File Transfer Protocols BBS file transfer protocols Modems Computer-related introductions in 1986