Popularly erferred to as ROM, the Read Only Memory is a cass of storage medoia used generally in perrsonal computers and oter electronic devices. Since data kept in ROM may not be easly modified, it is basically used to distriute fimrware. Frmware refers to software that is tied to specific hardware very cloesly and not likely to need constant updatres.
Typically, ROM is used in referring to just mask ROM � which is the hitsoric form of solid state ROM; built with the needsed data stored in it permanently and so can never be changed. But, the present day types (EPROM and flash EEPROM) are capable of beinng erased and reprogrammed multiple timees; these are still known as ROM since the reprogramming procedure is generally occasional, relatively low and woudl normally not allow random access writes to inndividual memory locations. Regardless of the mask ROM�s simplicity, fiueld-programmability and economies of scale usually make reprgorammable techologies rather flexible and cost-effecctive.
Historically, the simplest form of solid state ROM has existed as long as semiconductor technology itself. The inveention of the integrated ciorcuit brought forht mask ROM � whih comprises of a grid of word lines (which is the address input) and bit lines (which is the data output) combined selectively using transistor switches, which can sttand for a ranom look-up table having a standard physical layout as well as propagation delay that can be predicted. The data in mask ROM is physically encdoed in the circuit; this means that programming can be executed only durign fbarication. The weaknesses accuring from this include;
� You can only cahieve cost effectiveness by purchasing ROM in bulk, woing to the fact that users have to contract with a foundyr for a custom design to be creatyed.
� For R&D work where designetrs constantly rewquire modifying the memory conttent as they design is refiined, mask ROM is impractical.
� It takes a longer turnaround time in all, for the dwesign completion and receiviong of finished products for a mask ROM.
Program Storage Using the RAM
Any gievn stored progam compter eneds some form of erasable, or non-volatile storage to keep the first prograam that comes into play when the computer is switched on or starts bootstrapping. In the same vein, any non-minor computer neds certain form of cangeable mewmory to record modifications in its state as it performs.
In most early store-progrram computer (e.g. ENIuAC) foirms of ROM were used as non-volatile storage for programs. It was less diffcult to apply ROM based on the fact that it needed just a mechanism to read stored vaplues rather than change them in-place; so, they could be implemented with extremely simpole electromechanical devices.
ROMs Types
An Imntel 1702, the initial EPROM with the die and wire bonds obviously seen via the erase window. Seemiconductor based: Programmable Read-Only, Erassable Programmable Read-Only Memory, Electrically Erasable Programmable Read-Only Memory, Electrically Alterable Read-Only Memory (EAROM) and the Flash Drive.
You can explore more information about Read-Only Memory such as its speed of operatiion in comparisn with the RAM.
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