Word processing is the use of computers to type, edit, and print letters, reports, articles, and other documents. It has replaced typewriting for many tasks at home, in school, and in the office. Business people, authors, students, and lawyers turn to word processing as a tool for writing. Three main types of equipment are used for word processing: (1) personal computers, (2) dedicated word processors, and (3) electronic typewriters. Personal computers need special instructions called programs or software to perform word processing. Dedicated word processors are computers that do only word processing. Most dedicated word processors have built-in word processing software. Electronic typewriters resemble electric typewriters but include a built-in dedicated computer. The computer provides limited word processing capabilities, such as the ability to store and automatically type a small amount of text. Personal computers and dedicated word processors display characters on a computer screen as the user types them. Words, lines, paragraphs, and pages can be added, deleted, moved, or copied with a few keystrokes or the click of a button on a handheld control called a mouse. Most word processing programs and dedicated word processors enable the user to check for spelling errors. Many can check grammar in a limited way. At the touch of a key, the user can print out an entire document. The computer can store the document on a magnetic disk, so additional copies or corrections can easily be made later. In addition, most word processing programs for personal computers and some dedicated word processors can sort and merge lists and perform limited mathematical computations. Personal computers are the most powerful and versatile of the word processing machines. They can be programmed to do many things besides word processing. Computers can transfer information to other computers linked in a network or, using a device called a modem, send information over telephone lines. Personal computers are also the most expensive word processing machines. Dedicated word processors are a less expensive option for individuals and small businesses whose computer needs are limited to word processing. Electronic typewriters can perform only the most basic word processing functions, such as inserting, deleting, and underlining text. Most can also check for spelling errors. On many electronic typewriters, a small screen displays material as it is typed. Many electronic typewriters have a memory, but the amount of text it can store is much smaller than in a personal computer or dedicated word processor. Computer companies introduced relatively expensive dedicated word processors in the mid-1970's. Prices fell in the 1980's, and personal computers and word processing programs for personal computers became common. Personal computers are the most widely used form of word processor.