READ ONLY MEMORY(ROM)

ROM stands for "Read only memory".It is nonvolatile memory,i.e.the information stored in it is not lost even if the power supply goes off.It is used for permanent storage of information.It also possesses random access property. ROMs are much cheaper compared to RAMs  when produced in larger volumes.The stored information can only be read from ROMs at the time of operation.Information can not be written into a ROM by the users/programmers.In other words ROMs are not accessible to users.The contents of ROMs are decided by the manufacture.From programming mode point of view the ROMs  are placed in broad categories:masked-programmed and user-programmed. ROMs in which contents are written at the time IC manufacture are called mask-programmed ROMs. PROM,EPROM,E^2PROM  or any other kind of PROM are userprogrammable ROMs. If we supply write or say ROMs are are called PROM,EPROM,EEPROM etc.

ROMs store information which is not subject to change.They store fixed programs.In microprocessor-based systems which are used for industrial controls,ROMs store monitor,assembler,debugging package,function tables such as sine,cosine,logrithm,square root,exponential and code conversion tables,etc.