A canonical data model (CDM) is a type of data model that presents data entities and relationships in the simplest possible form. It is generally used in system/database integration processes where data is exchanged between different systems, regardless of the technology used. A canonical data model is also known as a common data model.
Read-only memory (ROM) is a type of storage medium that permanently stores data on personal computers (PCs) and other electronic devices. Because ROM is read-only, it cannot be changed; it is permanent and non-volatile, meaning it also holds its memory even when power is removed. By contrast, random access memory (RAM) is volatile; it is lost when power is removed.
Read-only memory (ROM) is a type of memory storage that is permanently integrated into a personal computer (PC). It contains the programming needed to start a PC, which is essential for boot-up; it performs major input/output tasks and holds programs or software instructions.
There are numerous ROM chips located on the motherboard and a few on expansion boards. The chips are essential for the basic input/output system (BIOS), boot up, reading and writing to peripheral devices, basic data management and the software for basic processes for certain utilities.
There are other types of non-volatile memory such as:
However, these types of non-volatile memory can be altered and are often referred to as programmable ROM. One of the original forms of non-volatile memory was mask-programmed ROM. It was designed for specific data such as bootstrap which contains the startup code. Mask-programmed ROM can never be changed.
Because ROM cannot be changed and is read-only, it is mainly used for firmware. Firmware is software programs or sets of instructions that are embedded into a hardware device. It supplies the needed instructions on how a device communicates with various hardware components. Firmware is referred to as semi-permanent because it does not change unless it is updated. Firmware includes BIOS, Erasable Programmable ROM (EPROM) and the ROM configurations for software.
ROM may also be referred to as maskROM (MROM). MaskROM is a read-only memory that is static ROM and is programmed into an integrated circuit by the manufacturer. An example of MROM is the bootloader or solid state ROM, the oldest type of ROM.
Some ROM is non-volatile but can be reprogrammed; this includes:
ROM is also often used in optical storage media such as various types of compact discs, including read-only memory (CD-ROM), compact disc recordable (CD-R) and compact disc rewritable (CD-RW).
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