Difference Between ROM and NVRAM
sivasakthi
I have heard a term like "NVRAM". Till my knowledge
goes, CMOS Memory (Battery backed RAM) and ROM are the only
non volatile forms of memory. What is the concept behind
NVRAM ? How is it used ?
Advanced thanks
Sivasakthivel
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Thomas Womack
"sivasakthi" <siva_sakt...@mailcity.com.invalid> wrote
> Hai All,
> I have heard a term like "NVRAM". Till my knowledge
> goes, CMOS Memory (Battery backed RAM) and ROM are the only
> non volatile forms of memory. What is the concept behind
> NVRAM ? How is it used ?
NVRAM is generally just another name for battery-backed RAM: the term's
normally used either to describe large buffers on RAID arrays designed so
that the data you write to the array will get written to the disk even in
the event of a power failure, or to describe the device storing the BIOS
configuration information on Sun or Apple systems -- the device called the
CMOS Memory in a PC context.
"CMOS Memory" is by now a rather unhelpful description -- as far as I
remember, all modern chips, and hence all the memory in any modern machine,
are manufactured in CMOS processes.
Did that help? Feel free to ask, if you have more questions.
Tom
t...@larva.flyingcroc.no.spam.please.net
>> Hai All,
>> I have heard a term like "NVRAM". Till my knowledge
>> goes, CMOS Memory (Battery backed RAM) and ROM are the only
>> non volatile forms of memory. What is the concept behind
>> NVRAM ? How is it used ?
>
>NVRAM is generally just another name for battery-backed RAM: the term's
>normally used either to describe large buffers on RAID arrays designed so
>that the data you write to the array will get written to the disk even in
>the event of a power failure, or to describe the device storing the BIOS
>configuration information on Sun or Apple systems -- the device called the
>CMOS Memory in a PC context.
Note, there are also some companies (IBM, and NonVolatile
Electronics) developing and deploying magelectric memory (MRAM),
which uses alloys which gain or lose magnetic properties when
current is applied, and do or do not (to a degree) conduct
electricity depending on those properties (and thus can be read
or written electronically). MRAM keeps its state without need
for refreshes for a very long time.
I've collected various mram-related documents here:
http://larva.flyingcroc.net/~ttk/public/mram/
-- TTK
Robert Hancock
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamhome.com
Home Page: http://members.home.net/hancockr
"sivasakthi" <siva_sakt...@mailcity.com.invalid> wrote in message
news:05108cf7...@usw-ex0108-062.remarq.com...
> Hai All,
> I have heard a term like "NVRAM". Till my knowledge
> goes, CMOS Memory (Battery backed RAM) and ROM are the only
> non volatile forms of memory. What is the concept behind
> NVRAM ? How is it used ?
>
Clifford A. Brown
NCR was using NVRAM in it's top of the line Cash Registers (Class 2140)
in the late 70's and early 80's. This NVRAM I believe used tunnel
diodes to store the data. The memory chip had two sections, nonvolatile
and volatile. When the cash register was powered up the CPU would get
the data out of the non volatile area and put it in the volatile area
because that memory ran faster. If the power was removed or the system
was put in standby (there was no on/off switch on this cash register)
then the cpu would drop what it was doing and go through all the NVRAM
and transfer the data back into the non-volatile part of the chip. It
had some really big capacitors in the power supply to give the cpu time
to do that.
We also had a cash register (Class 2126) that used bubble memory.
Remember that?
Cliff Brown