Also contained in the frame or cabinet of the computer  is  the  peripheral  equipment-floppy  and/or hard disk units. Computers that use motherboards or backplanes use a keyboard external to the frame or cabinet as their method to control the computer.  With some micros, however, the keyboard is part of the cabinet  assembly. The  motherboard  or  backplane usually rests on the bottom of the frame or cabinet of the computer. The motherboard or backplane contains all the pcb’s for the whole computer, a keyboard connector, a battery backup circuit, and power supply status LEDs. A motherboard has IC chips included on the motherboard; a backplane does not. Each pcb contains one or more functional areas. Figure 2-13 is an illustration of a motherboard or backplane design used in a computer. It is easier to perform maintenance on computers with motherboards or backplanes than on modular- or chassis-designed  computers  because  of  their  size  and the easy accessibility to the interior of the computer. Extending  pcb’s  for  maintenance  is  usually  not necessary because everything can be readily accessed once the cover is removed; this includes maintenance with the power still applied. Remember, you must still exercise  safety  precautions  when  removing  and installing any parts inside the frame or cabinet by securing power to the computer. Safety and Security Design Features of Computer Frames/Cabinets The  frame  or  cabinet  can  provide  limited  protection for a computer by use of gaskets and filters. Gaskets and filters are not used on all types of computers, but they serve important safety and security functions on those where they are used. GASKETS.  —Gaskets are used for two main purposes on computers. Gaskets provide moisture sealing  protection  and  protection  against  interference (radio   frequency   interference   [RFI]   and electromagnetic  interference  [EMI]).  The  gaskets  are usually located around the edges of an item to protect its contents or internal parts. For example, gaskets are used in heat exchangers for a module to protect the pcb’s inside  the  module  from  moisture  and  electronic interference. Gaskets  are  also  used  in  electrical connectors inside a frame or cabinet to protect the connection from electronic interference. FILTERS. —There are two types of filters you will encounter. They are electronic (EMI and RFI) and environmental (foreign particles such as dust and dirt) filters.  Both  filters  provide  protection  for  the  computer. The computer’s technical manual and/or the Planned Maintenance System (PMS) will provide you with the requirements for the maintenance of these two filter types. Figure  2-13.—Example  of  a  motherboard-  or  backplane-designed  computer. 2-12