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WardXmodem (talk | contribs) Add details of how Ymodem came about, from personal experience (phone call with Chuck) |
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The widely adopted [[ZMODEM]] used a [[sliding window protocol]]. Rather than wait for positive acknowledgment after each block is sent, it sent blocks in rapid succession and resent unacknowledged blocks later. By avoiding delays due to [[latency (engineering)|latency]], the bandwidth usable for transmission more closely approached the [[bandwidth (computing)|bandwidth]] of the underlying link. ZMODEM could also resume interrupted transfers without retransmitting the already-received blocks. In addition to developing the protocol, Forsberg developed [[software]] for sending and receiving files using ZMODEM.
Chuck then wrote a version Zmodem G, which was for use over "guaranteed error free" communications lines, such as Ethernet or short serial-to-serial computer connections. This protocol waived the usual retransmission overhead, to send files as fast as possible.
Originally, he wrote a program for Unix called rbsb (receive batch / send batch) which used block 0 to transmit a file's name, and optionally date and time, since [[Ward Christensen]] designed [[Xmodem]] to start at block 1, leaving block 0 ''available''. At one point Ward, in a phone call to Chuck, suggested calling his protocol [[Ymodem]] because it was "one better" than [[Xmodem]]. Chuck created the program ''YAM'' which in traditional Unix nomenclature, stood for ''Yet Another Modem'' after "Modem.asm" the original version of [[Xmodem]] released by Ward in the CP/M User's group in 1977.
Forsberg most recently resided in [[Portland, Oregon]] prior to his death. He ran data transmission software company Omen Technology which he founded in 1984.<ref name="autogenerated1">{{cite web |url=http://www.omen.com/about.html |title=About Omen Technology |accessdate=2012-02-16 |deadurl=bot: unknown |archiveurl=https://web.archive.org/web/20150915193210/http://www.omen.com/about.html |archivedate=September 15, 2015 |df= }}</ref> He was an amateur radio operator (call sign WA7KGX)<ref>{{cite web | url = http://wireless2.fcc.gov/UlsApp/UlsSearch/license.jsp?licKey=862831 | title = Amateur License – WA7KGX – FORSBERG, CHARLES A | accessdate = 2012-02-16}}</ref> and a licensed aircraft pilot.<ref name="autogenerated1"/>
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