CHAPTER 12  Textfile Input and Output  Communication between people and computer systems was already  mentioned in Chapter 9, File Types. Both learn to  understand  through  what  is  termed  pattern  recognition.  Unfortunately,  the  patterns  recognized most easily by people (mainly those of picture and sound)  are very different from those acceptable to computer systems (electrical  impulses). In fact,  the expense of physically transmitting data - implying a translation of patterns legible to people into those legible to  computer systems and vice versa - can be as costly as the processing of  the data itself. (Consequently, much research is devoted to minimizing  the cost by "automating" more of the translation process.) This task of  communication is called input and output handling (I/O).  People can transmit information to computer systems via  input  devices  and  media  (e.g., keyboards, diskettes, pointing devices, tape  cartridges, optical discs, magnetic tapes, terminals) and receive results  via  output devices  and  media  (e.g., printers, magnetic tapes, diskettes,  tape cartridges, optical discs, plotters, speakers, and video displays).  What is common to most of these - and defined by each individual  computer installation - is a set of legible characters (Chapter 2). It is  over this character set that Pascal defines the standard type  Text  (see  Chapter 9).  It is important to remember that each such input-output device  enforces certain conventions as to the meaning of specific characters  and patterns (strings) of characters. For example, most printers enforce  some maximum line length. Also, many older line printers interpret the  127 