Because of these traits and its availability as Open Source software, sendmail has proved critical to the growth of electronic mail usage. Eric Allman, co-founder and CTO of Sendmail, Inc., wrote the original sendmail program while at the University of California at Berkeley. Source Code Programming statements and instructions written by a programmer. Source code is what a programmer writes, but it is not directly executable by the computer. It must be converted into machine language, the language that the computer understands.
Source code is the only format that is readable by humans.
When you purchase programs, you usually receive them in their machine-language format. This means that you can execute them directly, but you cannot read or modify them. Increasingly software manufacturers are providing their source code, see Open Source. A powerful interpreted programming language developed by John Ousterhout. One of the main strengths of Tcl is that it can be easily extended through the addition of custom Tcl libraries.