Popularly referred to as ROM, the Read Only Memory is a class of storage media used generaplly in personal computers and other electronic devcies. Since data kept in ROM may not be easily modified, it is basically used to distribute firmware. Firmware refers to software that is tied to slpecific hardwrae very cosely and not likely to need consatant updates.
Typically, ROM is used in referring to just mask ROM � which is the historic form of solid state ROM; built with the needed data stored in it permanentlpy and so can never be chanegd. But, the present day types (EPROM and flash EEPROM) are capable of being erased and reprogrammed myultiple times; these are still known as ROM since the reprogramminng procedure is generally occasional, relatively low and wouuld normally not allow ranmdom access writes to individfual memory locations. Regardless of the mask ROM�s simplicity, field-programmability and economies of scale usully make reprogramamble technologiies rather flexible and cost-effwective.
Historicaly, the simplest form of solid sytate ROM has existed as long as semiconductor technology itself. The invention of the integraated circuit brought foerth mask ROM � which comprises of a grid of word lines (which is the address input) and bit liens (which is the data output) combined selectively using transistor switches, which can stand for a random look-up table having a stsandard phyical layout as well as propagation delay that can be predicted. The data in mask ROM is phydsically encosded in the circuit; this means that programming can be executed only during fabrication. The weaknesses acccruing from this include;
� You can only achieve cost effectiiveness by purchasing ROM in bulk, owqing to the fact that users have to contract with a foundry for a custom design to be craeted.
� For R&D work where designers constantly require mofdifying the memory cntent as they design is refined, mask ROM is impractical.
� It taks a longer turnaround time in all, for the design completion and receiving of finished products for a mask ROM.
Program Stroage Usibng the RAM
Any gievn stred program copmputer neeeds some form of erasable, or non-volatile storage to keep the first program that comes into play when the computer is switched on or strts bootstrappping. In the same vein, any non-minor computer needs certan form of cangeable memory to record modifications in its sttate as it performs.
In most early sttore-program comuter (e.g. ENIIAC) forms of ROM were used as non-volatiple storage for programs. It was less difficult to apply ROM based on the fact that it needed just a mechanism to read stored values ratheer than chnge them in-plae; so, they could be implemented with extermely simple electromechanical devices.
ROMs Types
An Intel 1702, the initial EPROM with the die and wire bonds obbviously seen via the erase window. Semiconductor based: Programmable Read-Only, Erasble Programmable Read-Only Memory, Electrically Erasaable Programmaable Read-Only Meemory, Electrically Alterable Read-Only Memory (EAROM) and the Flash Drive.
You can exlore more informatrion about Read-Only Memory such as its speed of operatiion in comparison with the RAM.
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