<P> In the context of the ALGOL 68 programming language, the input and output facilities are collectively referred to as transput . The ALGOL 68 transput library recognizes the following standard files / devices: stand in, stand out, stand errors and stand back . </P> <P> An alternative to special primitive functions is the I / O monad, which permits programs to just describe I / O, and the actions are carried out outside the program . This is notable because the I / O functions would introduce side - effects to any programming language, but this allows purely functional programming to be practical . </P> <P> Channel I / O requires the use of instructions that are specifically designed to perform I / O operations . The I / O instructions address the channel or the channel and device; the channel asynchronously accesses all other required addressing and control information . This is similar to DMA, but more flexible . </P> <P> Port - mapped I / O also requires the use of special I / O instructions . Typically one or more ports are assigned to the device, each with a special purpose . The port numbers are in a separate address space from that used by normal instructions . </P>

What is the main function of i/o interface module