The message portion of a data block in synchronous data transmissions.
Turnaround Time
The time required to reverse the direction of transmission when operating in half duplex mode.
U
Upload
Refers to sending files or text from the user’s computer to another user, a bulletin board or videotex system. (Many bulletin boards that offer public domain software encourage users to upload their own programs so that other users can download them).
V
Vertical Redundancy Check (VRC)
A method of character parity checking.
Videotex
An interactive information system which is also known as Videotext or Viewdata. Videotex systems usually operate over switched telephone lines and allow 40 columns by 24 lines of colour text and graphics to be displayed on the screen. Information is arranged in pages, each page having a unique page number. Well known videotex systems include Prestel (Britain), Discovery 40 (Australia), and Minitel (France). See also Teletext.
Videotext
See Videotex.
Voice Grade Line
Channel with a frequency range of 300 to 3400 Hz suitable for the transmission of speech or data in analog form.
X
XModem
A communications protocol developed in the late ’70s by Ward Christensen to perform error checking on data being sent between two computers.
XON/XOFF
Special control characters used to control the flow of data between your computer and a remote system. See Software Handshaking.
Y
Y Modem
Page 282
