Figure  1-22.—External  hard  disk  drive  with  removable  disk cartridge. Printers Most printers you are likely to use while working on microcomputers are the low-speed varieties. They are able to print text at rates of 200 to 800 characters per second   and   usually   output   this   information   one character-at-a-time. After close examination, you will find  that  basically  the  only  major  difference  between printers designed for micros and those used on larger mainframes is their size, and the speed at which they print. Other than that, they are very much alike in terms of setup, operation, and operational features. Micro printers, like mainframe printers, are either impact  or  nonimpact.  At  least  six  printing  technologies are  used  to  produce  hundreds  of  microcomputer  printer models. These technologies include dot-matrix (which forms  characters  using  a  series  of  dots),  xerographic, electrostatic, ink jet, and laser. DOT-MATRIX   PRINTER.—   The  dot-matrix printer uses a print head made up of pins. It creates the characters by using these pins to generate characters a dot-at-a-time.   Dot-matrix   printers   have   speeds   that range from 60 to 350 cps. XEROGRAPHIC   PRINTERS.—   Xerographic printers  use  a  printing  technique  very  similar  to  the methods used in duplicating or copying machines. The printers  can  operate  at  speeds  up  to  4,000  lines  per minute. ELECTROSTATIC PRINTERS.—  Electrostatic printers  use  a  special  photographic  paper  that  allows characters to be etched onto the paper using a stylus. The stylus, made up of tiny wires, forms characters by placing  an  electrostatic  charged  image  on  the  paper. Then, as the paper is moved through a toner solution containing ink particles, the ink adheres to the charges that form a pattern on the paper to develop the character. This type of printer can be used for both printing and plotting (displaying graphic output), and can print up to 5,000 lines per minute. INK JET PRINTERS.—  Ink  jet  printers  employ  a technique very similar to the way we use a can of spray paint and a stencil. A spray of electrically charged ink is shot  (under  pressure)  toward  the  paper.  Before  reaching the paper, the ink is passed through an electrical field, which  forms  the  letters  in  a  matrix  form.  The  print resulting  from  this  process  consists  of  easy  to  read, high-quality characters. Some manufacturers use large droplets of ink for faster printing, while others use small droplets  for  better  clarity  but  with  slightly  reduced printing speeds. This type of printer can print up to 300 characters per second. LASER  PRINTERS.—  Laser  printers  direct  a beam of light through a rotating disk containing the full range  of  print  characters. The  appropriate  character image  is  directed  onto  photographic  paper,  which  is then put through a toner, developed, and used to make additional copies. The print resulting from this process consists of sharp, clean images that are easy on the eyes. These  printers  can  print  up  to  20,000  plus  lines  per minute. Many   micro   printers   can   print   subscripts   and superscripts,  print  in  several  different  colors,  print graphic  material,  and  output  text  in  several  different type  styles  (fonts). Some printers print in a single direction only, like the  conventional  typewriter,  whereas  others  print  in both   directions   (bidirectional)   to   save   on   time- consuming carriage returns. Many come with either a friction  feed  (for  handling  single-sheet  paper)  or  an adjustable  tractor  feed  (for  handling  continuous  forms), and some even have both. You can initiate a wide range of printer functions either   through   the   applications   program   you   are working with or by using the controls located on the front of the printer’s operating panel. These controls can be buttons, lights, and switches. With a simple touch of a button, you can change such things as type style, letter quality, pitch, and spacing. It’s that simple. As mentioned, most printers are equipped with an operating  control  panel  that  allows  you  to  change various settings. For  example,  you  can  change  the number of characters per line or lines per inch, change fonts  and  type  size,  and  switch  from  draft  to  letter- quality  mode. You  can  choose  any  combination  of 1-21