system makes all the difference in the world in terms of internal   processing   speeds   (33MHz,    66MHz, 120MHz, and so on), number of bits handled  (8, 16, or 32 bits), memory size  (640K, 4M, 16M, and up), and the applications software it will run. Each   microcomputer   contains   a   specific microprocessor   chip   as   its   main   processor.   A microprocessor chip can typically handle 8, 16, or 32 bits  of  information  at  once.  Generally  speaking,  the more bits a computer can manipulate at one time, the faster it can process program instructions and data, and the  larger  the  main  or  primary  memory  it  can accommodate.  The  type  of  chip  in  your  computer  or system unit also has a great effect on what you can do with  your  micro.  For  example,  operating  systems  are written  to  serve  a  specific  microprocessor  chip,  and applications  programs  that  work  under  one  operating system are not likely to work under another unless the program   is   modified.   Many   applications   programs come in several versions to provide compatibility with several operating systems. These are just a few of the reasons why we say it is very  important  that  you  read  all  the  documentation that comes with your microcomputer. The Navy uses many   different   types   of   microcomputers   and microprocessor  chips. To  give  you  an  idea  of  the variety, table 1-1 lists some of the microprocessor chips. Specialized Processors Specialized processor chips have been developed to shift   some   of   the   workload   from   the   main Table  1-1.—Microcomputer  Chips  and  Microcomputers microprocessor chip. For example, IBM uses an Intel 8048 chip on the keyboard to determine which keys are being  depressed  and  also  to  check  to  see  that  the keyboard   is   communicating   properly   with   the microprocessor. In fact, most peripheral devices have one or more specialized processors embedded in them. Other  specialized  processors  are  the  Intel  80287 and   the   faster   80387   math   coprocessor.   These   are special-purpose   programmable   microprocessors designed to perform arithmetic calculations up to 100 times  faster  than  the  main  microprocessor.  A  math coprocessor  executes  arithmetic  instructions  that  would normally  be  handled  by  the  main  microprocessor’s arithmetic-logic unit (ALU) as well as those the main microprocessor   cannot   perform   because   of   register constraints.  The  80287  and  80387  are  companion  chips to   the   Intel   family   of   microprocessors.   Computer systems using the 80 series of chips are capable of very high-speed  mathematical  operations  when  the  math coprocessor  chip  is  plugged  either  into  or  alongside  the system  or  motherboard.  Math  coprocessor  chips  are used in SX version computers. The SX denotes that the computer does not have a math coprocessor integrated into the cpu chip. A DX version computer has a math coprocessor  integrated  into  the  cpu  chip.  With  the development  of  the  Pentium  chip,  math  coprocessor chips  were  no  longer  required  to  perform  arithmetic calculations. INPUT/OUTPUT  DEVICES  AND ACCESSORIES To   the   system   unit   we   must   add   input/output devices to communicate between us and the computer. These include the monitor, the keyboard, disk drives, and the printer. We will look at each of these devices in the  following  sections,  along  with  some  of  the  more common  accessories  found  on  microcomputers,  such  as surge protectors, parallel to serial converters and vice versa,  null  modems,  cables,  and  switches  used  for sharing hardware. Monitors (Display Devices) Monitors   are   used   as   output   devices   on microcomputers. They   are   peripheral   devices   that contain a display like a television viewing screen. They are   the   principal   link   between   you   and   the microcomputer. Their sole purpose in life is to allow the microcomputer to communicate its actions to you (the user), so you can act upon those actions to accomplish whatever job you are doing. They display output from the computer. The monitor is one of the most important peripherals to a micro and is certainly the most visible. 1-14