Alan Freedman -- The Computer Language Company - Computer Desktop Encyclopedia
Computer Desktop Encyclopedia
Longest-Running Tech Reference on the Planet

A CDE Definition

You'll love The Computer Desktop Encyclopedia (CDE) for Tech Term of the Day (TTOD)



A file transfer protocol that was very popular during the days of analog modem transmission between bulletin boards because it handled noisy and changing line conditions very well, including satellite transmission. Funded by the Telenet packet network and developed by Chuck Forsberg in the mid-1980s, Zmodem uses a sliding window design, which is faster than the Xmodem and Ymodem protocols that came before it. The TCP protocol also uses a sliding window (see sliding window).

Using variable length blocks and CRC error correction, Zmodem first sends file name, date and size before sending the data. The receiver continuously sends back the starting location of the next part of the file that is required so that crash recovery can be easily implemented by the file transfer program if the transmission fails in the middle. Many popular communications programs offer Zmodem as a file transfer option.

Industrial Zmodem
As a compact and proven protocol, Zmodem is used for embedded systems. Although residing in the public domain specifically for Unix systems, the heart of the protocol is available as Industrial Zmodem, a commercial product from Forsberg's company. For more information, visit

sliding window

(1) A communications protocol that transmits multiple packets before acknowledgment. Both ends keep track of packets sent and acknowledged (left of window), those which have been sent and not acknowledged (in window) and those not yet sent (right of window).

(2) A view of memory that can be instantly shifted to another location.

Personal Use Only

Before/After Your Search Term
Zip diskZoho
Zip drivezombie
ZIP filezombie bot
zip tonezombie script
zipped archivezone
zipped filezone bit recording
zippingzone CAV
zlibzone CLV

Terms By Topic
Click any of the following categories for a list of fundamental terms.
Computer Words You Gotta KnowSystem design
Job categoriesUnix/Linux
Interesting stuffPersonal computers
InternetIndustrial Automation/Process Control
Communications & networkingAssociations/Standards organizations
HistoryDesktop publishing
ProgrammingHealthcare IT
System design