255. Windowed versions used this packet number to indicate which packets had been received properly, or specify one that had not. Since the packets were 128 bytes long, this meant the maximum amount of data that could be transferred before the packet numbers rolled over was 32 kB. ZMODEM replaced the packet number with the actual location in the file, indicated by a 32-bit number. This allowed it to send messages that re-wound the transfer to the point of failure, regardless of how long the file might be. This same feature was also used to re-start transfers if they failed or were deliberately interrupted. In this case, the receiver would look to see how much data had been previously received and then send a with that location, automatically triggering the sender to start from that point. Auto-start Auto-starting simplified management by allowing the sending machine to start the transfer. Previously the user had to first request the file from the sender, placing it into a "waiting" state, then return to their local program and invoke a command to start the transfer. With auto-transfer, they simply requested the file, the sender would then automatically trigger the transfer in the user's program. Variations A number of modified versions of ZMODEM appeared. ZedZap was a variant of ZMODEM with 8 kbyte blocks for better performance on high-speed modems. LeechZmodem was a mischievous ZMODEM variant (among similar XMODEM and YMODEM derivatives) that cheated BBS download quotas. A backwards compatible extension of ZMODEM with 32 kbyte and 64 kbyte block lengths was created by ADONTEC in 2002 and 2007 to increase performance on high-speed error free connections like ISDN or TCP/IP networks. The most notable ZMODEM implementations were from Chuck Forsberg's Omen Technology, Inc. These included DSZ (DOS Send ZMODEM), GSZ (Graphical Send ZMODEM), and the ubiquitous (l)rzsz for Unix variants. In more current times, the developers of Synchronet have created a modern X/Y/ZMODEM implementation named SEXYZ, loosely based on the zmtx/zmrx package, which runs natively on Windows and Unix variants, supports long filenames and faster, more reliable data transfers. The ZMODEM implementation from SEXYZ has also been incorporated into the SyncTERM project. Synchronet, SEXYZ, and SyncTERM are all open-source, cross-platform, BBS-centric projects. Forsberg himself collected a number of improvements into ZMODEM-90. The first of these is MobyTurbo, which removed control quoting to further improve performance, about 15%. Even on networks that "eat" control characters,