A manufacturer programmed rom is one in which data is

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Unformatted text preview: ll the operations of the computer system. ROMs are mainly used by computer manufacturers for storing these microprograms so that they cannot be modified by the users. A good example of a microprogram that is stored in a ROM chip of a computer is the set of instructions that is needed to make the computer system ready for use when its power is switched on. This microprogram called "system boot program", contains a set of startup instructions to check if the system hardware like memory, I/O devices, etc. are functioning properly, and looks for an operating system and loads its core part in the volatile RAM of the system to produce the initial display-screen prompt. Note that this microprogram is used every time the computer is switched on and needs to be retained when the computer is switched off. Hence ROM is an ideal storage for this microprogram. There are two types of read-only memory (ROM) - manufacturer-programmed and userprogrammed. A manufacturer-programmed ROM is one in which data is burnt in by the manufacturer of the electronic equipment in which it is used. For example, a personal computer manufacturer may store the system boot program permanently in the ROM chip used on the motherboard of all the PCs manufactured by it. Similarly, a printer manufacturer may store the printer controller software in the ROM chip used on the circuit board of all the printers manufactured by it. Manufacturer-programmed ROMs are mainly used in those cases where the demand for such programmed ROMs is large. Note that manufacturer-programmed ROM chips are supplied by the manufacturers of electronic equipment, and it is not possible for a user to modify the programs or data stored inside the ROM chip. On the other hand, a user-programmed ROM is one in which the user can load and store "read-only" programs and data. That is, it is possible for a user to "customize" a system by converting his/her own programs to microprograms and storing them in a user-programmed ROM chip. Such a ROM is commonly known as Programmable Read-Only Memory (PROM) because a user can program it. Once the user programs are...
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