READ ONLY MEMORY

2. DEFINITION:
Read Only Memory (ROM) is computer
memory that can always store data and
applications within it. There are various
types of ROM with names like EPROM
(Erasable ROM) or EEPROM (Electrically
Erasable ROM).
MEANING:
ROM is "in-built" computer memory
containing data that normally can only be
read, not written to. ROM contains the
programming that allows your computer to
be "booted up" or regenerated each time
you turn it on. Unlike a computer's random
access memory (RAM), the data in ROM is
not lost when the computer power is turned
off. The ROM is constant by a small longlife battery in your computer.

3. IntroductIon to
non-volatIle MeMorY
The non-volatile memory such as erasable programmable read only memory
(EPROM) and electrically erasable programmable read-only memory (EEPROM
or Flash ROM) are sometimes referred to, in an abbreviated way, as "read-only
memory" (ROM); although these types of memory can be erased and reprogrammed multiple times, writing to this memory takes longer and may
require different procedures than reading the memory. When used in this less
precise way, "ROM" indicates a non-volatile memory which serves functions
typically provided by mask ROM, such as storage of program code and nonvolatile data.

4. HIStorY
The simplest type of solid state ROM is as old as semiconductor technology itself.
Combinational logic gates can be joined manually to map n-bit address input onto arbitrary
values of m-bit data output (a look-up table). With the invention of the integrated circuit came
mask ROM.

PROM, invented in 1956, allowed users to program its contents exactly once by
physically altering its structure with the application of high-voltage pulses.

The 1971 invention of EPROM essentially solved problem 3, since EPROM can
be repeatedly reset to its un-programmed state by exposure to strong ultraviolet light.

EEPROM, invented in 1983, went a long way to solving problem 4, since an
EEPROM can be programmed in-place if the containing device provides a means to receive
the program contents from an external source .

Flash memory, invented at Toshiba in the mid-1980s, and commercialized in the
early 1990s, is a form of EEPROM that makes very efficient use of chip area and can be
erased and reprogrammed thousands of times without damage.
All of these technologies improved the flexibility of ROM, but at a significant
cost-per-chip

5. USE FOR inSTORING DATA
Since ROM (at least
hard-wired
mask form) cannot be modified, it is really only
suitable for storing data which is not expected to
need modification for the life of the device. To
that end, ROM has been used in many
computers to store look-up tables for the
evaluation of mathematical and logical
functions (for example, a floating-point unit
might tabulate the sine function in order to
facilitate faster computation). This was
especially effective when CPU’s were slow and
ROM was cheap compared to RAM.
The use of ROM to store such small
amounts of data has disappeared almost
completely
in
modern
general-purpose
computers. However, Flash ROM has taken
over a new role as a medium for mass storage or
secondary storage of files.

6. SPEED
READING
Although the relative speed of RAM vs. ROM has varied over time, as of 2007 large
RAM chips can be read faster than most ROMs. For this reason (and to allow uniform
access), ROM content is sometimes copied to RAM or shadowed before its first use,
and subsequently read from RAM.
WRITING
For those types of ROM that can be electrically modified, writing speed is always much
slower than reading speed, and it may need unusually high voltage, the movement of
jumper plugs to apply write-enable signals, and special lock/unlock command codes.
Modern NAND Flash achieves the highest write speeds of any rewritable ROM
technology, with speeds as high as 15 MB/s (or 70 ns/bit), by allowing (needing) large
blocks of memory cells to be written simultaneously.

7. CONTENT IMAGES

The contents of ROM chips in video game support holders can be extracted with
special software or hardware devices.

The resultant memory dump files are known as ROM images, and can be used to
produce duplicate units, or in support emulators.

The term originated when most console games were distributed on units containing
ROM chips, but achieved such general usage that it is still applied to images of fresher games
distributed on CD-ROM’s or other optical media.

ROM images of commercial games usually contain copyrighted software.

There is a successful community busy in the illegal distribution and trading of such
software.

In such circles, the term "ROM images" is sometimes reduced simply to "ROMs" or
sometimes changed to "romz" to highlight the connection with "warez".

8. LOGO
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