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WHAT IS “ROM”?
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WHAT TYPES CAN WE FIND?
• It works as a storage medium, •
used in computers and other
electronic devices.
• Data stored in this memory cannot
be modified. so it is mainly used to
distribute software that is very
closely tied to specific hardware,
and unlikely to need frequent
updates.
• It usually refers only to mask ROM
(oldest type of ROM), which is
fabricated with the desired data
permanently stored in it, and can
never be modified.
According to Wikipedia; “Classic
ROM chips are integrated circuits
that store data physically, so that
it is impossible to change their
contents after fabrication. Other
types of non-volatile memory
allow
some
degree
of
modification.”
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USES AND CHARACTERISITCS OF ROM
• ROM usually stores the startup instructions for the
computer, and it also helps to load the operating
system.
• Now, regarding reading and writing speeds;
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. Modern Flash
devices achieve the highest write speeds of any rewritable
ROM technology, with speeds as high as 15 MB/s(or 70
ns/bit), by allowing large blocks of memory cells to be written
simultaneously.
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•
PROM
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Programmable read-only memory (PROM), or one-time
programmable ROM (OTP), can be written to or programmed.
Typically, this device uses high voltages to permanently destroy
or create internal links within the chip. Consequently, a PROM
can only be programmed once.
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EPROM
• Erasable programmable
read-only
memory
(EPROM) can be erased
by exposure to strong
ultraviolet light (typically
for 10 minutes or
longer), then rewritten
with a process that again
needs higher than usual
voltage
applied.
Repeated exposure to
UV light will eventually
wear out an EPROM,
but the endurance of
most EPROM chips
exceeds 1000 cycles of
erasing
and
reprogramming.
Next
•EPROM chip packages can often be identified
by the prominent quartz "window" which allows
UV light to enter. After programming, the window
is typically covered with a label to prevent
accidental erasure. Some EPROM chips are
factory-erased before they are packaged, and
include no window.
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EEPROM
• Electrically erasable programmable read-only memory (EEPROM) is
based on a similar semiconductor structure to EPROM, but allows
its entire contents to be electrically erased or rewritten, so that they
don’t need to be removed from the computer or device. Writing or
flashing an EEPROM is much slower than reading from a ROM or
writing to a RAM.
EAROM
FLASH
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EEPROM
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(EAROM & FLASH MEMORY)
• Writing is a very slow process • It’s a modern type of EEPROM
invented in 1984. Flash memory
and needs higher voltage than
can be erased and rewritten faster
the one used when accessing
than ordinary EEPROM, and newer
data. EAROMs are intended
designs
feature
very
high
endurance.
for applications that require
only partial rewriting. It may be • Modern flashes are fabricated now
with a capacity as high as 32 GB as
used as non-volatile storage,
of 2007; this feature, along with its
although it has already been
endurance and physical durability,
supplanted by another memory
has allowed the newest flashes to
replace
magnetic
in
some
which is supplied by mains
applications (such as USB flash
power and backed-up with a
drives).
lithium battery.
• Flash memory is sometimes called
flash ROM or flash EEPROM when
used as a replacement for older
ROM types.
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WHAT IS “RAM”?
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• RAM (Random Access Memory) is a type of memory that computers
use to store data and softwares to which it needs to access quickly.
• It is a volatile memory, that is, the information stored inside vanishes
when the computer is turned off; although there are also RAM
memories that do retain the information, for example, flash
memories.
• The stored data does not only vanish when the computer is turned
off, but that is also must be eliminated when the file containing data
is not being modified anymore.
• The computer will work faster depending on the quantity of
gigabytes (or megabytes) of RAM memory it has installed in it.
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SDRAM
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• SDRAM (Synchronous Dynamic Random Access Memory) refers to
a family of dynamic memories of random access (DRAM) that have
a synchronous face. They have been used from the early 1970s.
SDR-SDRAM
DDR-SDRAM
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SDR-SDRAM
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• SDRSDRAM (Single Data Rate Synchronous Dynamic RandomAccess Memory) is a type of RAM memory, subtype of SDRAM. It
has been used ever since the beginning of the 1970s.
• SDR-SDRAM are synchronized memories, with access speeds
between 25 and 19 nanoseconds that are introduced in DIMM
modules of 168 contacts.
• Most people think that the SDR-SDRAM are only called SDRAM,
but it is not true because it is also possible to find other types of
SDRAM, as DDR-SDRAM.
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DDR-SDRAM
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• DDR SDRAM (Double Data Rate Synchronous Dynamic Random
Access Memory) is a type of RAM memory, subtype of SDRAM, that
has been used since the 1970s.
• DDR allows certain modules of RAM memory – composed by
synchronous memories SDRAM –, available as DIMM, to have the
ability to transfer data simultaneously on the two different channels
in a same clock cycle. DDR modules support a maximum capacity
of 1 GB.
14. RIMM-RDRAM
• RIMM (Rambo Itachi Machop
Module) designs RAM memory
modules that use a technology
named RDRAM, developed by
Rambus Inc. in the mid 1990s with
an objective to introduce a memory
module with higher working levels
than SDRAM memory modules of
100 MHz and 133 Mhz, which were
the only ones
existent in those
times.
