How many transistors to store a bit? (Flash ROM)
Al Borowski
I was thinking today about how incredibly integrated things like
memory are. I was wondering - how many transistors are needed to store
a bit?
Suppose I idly include the string "Hi World" in the flash ROM of a
microcontroller. This string does nothing except waste space.
That's 64 bits I have just used. How many transistors have I just
wasted?
thanks,
Al
Robert Baer
With the proper design and processing, the answer is "ONE".
And the message can be compressed slightly in a manner that simple
logic can expand - that would take a little as zero transistors; total
maximum count of 32.
Al Borowski
>
>
> With the proper design and processing, the answer is "ONE".
> And the message can be compressed slightly in a manner that simple
> logic can expand - that would take a little as zero transistors; total
> maximum count of 32.
Thanks for the reply, but I think you missed my intention.
Suppose I include the string, without any attempts at optimizing. EG no
compression, etc. I just want to know how many transistors it takes to
store the string as is (64 bits).
cheers,
Al
Russell Powell
A single transistor (and capacitor) may be used to store 1 bit
of information - as in the case of a DRAM. (There is now a 1T
SRAM cell but it's not yet in high production use). A standard
SRAM will use six transistors to store 1 bit of information.
Hence, to store 64 bits in DRAM - 64 transistors. In SRAM,
384 transistors. This accounts only for the storage cells and not the
memory periphery logic.
--
sincerely,
Russell Powell
Artisan Components
SR. FAE - U.S. Central
rpo...@artisan.com
469-438-6589
"Al Borowski" <a.bor...@student.qut.edu.au> wrote in message
news:3f71594a$0$23606$5a62...@freenews.iinet.net.au...
wally
Russell Powell wrote:
> As a memory designer for many years, this is up my alley.....
> A single transistor (and capacitor) may be used to store 1 bit
> of information - as in the case of a DRAM. (There is now a 1T
> SRAM cell but it's not yet in high production use). A standard
> SRAM will use six transistors to store 1 bit of information.
>
> Hence, to store 64 bits in DRAM - 64 transistors. In SRAM,
> 384 transistors. This accounts only for the storage cells and not the
> memory periphery logic.
if you are writing the data to a non volatile memory (flash is an
example) you could say that each bit would be one transistor. But, other
devices will be involved (for high-voltage control , address decoding,
etc. So your Q will have different answers depending on the type of
memory you are writing too. DRAM is definitly the most dense though,
with a bit per storage device as Russell pointed out. Russell, a Q for
you, do you know of a NG which concentrates more on IC design than this
one, which is more general? cheers.
Goran Larsson
wally <wally...@hotmail.com> wrote:
> if you are writing the data to a non volatile memory (flash is an
> example) you could say that each bit would be one transistor. But, other
> devices will be involved (for high-voltage control , address decoding,
> etc. So your Q will have different answers depending on the type of
> memory you are writing too. DRAM is definitly the most dense though,
> with a bit per storage device as Russell pointed out.
Both DRAM and Flash can be made with methods that store more than one bit
per transistor. They do this by storing different charge levels in the
transistor. Using two charge levels gives one bit, using four discrete
charge levels gives two bits, and so on.
The intel strataflash memory introduced in 1997 has flash memory
cells/transistors that can have four discrete charge levels in their
floating gates. The four charge levels are used to encode two logical bits.
AMD, Fujitsu and Saifun will introduce a new flash memory type in 2004
that can store 4 bits per cell/transistor.
--
Göran Larsson http://www.mitt-eget.com/
Russell Powell
alt.electronics,
alt.electronics.analog,
rec.electronics,
sci.electronics.cad (for more of the EDA type questions)
and
sci.eclectronics.design (more active than any of the others)
--
sincerely,
Russell Powell
Artisan Components
SR. FAE - U.S. Central
rpo...@artisan.com
469-438-6589
"wally" <wally...@hotmail.com> wrote in message
news:3F71AA54...@hotmail.com...
Keith R. Williams
@comcast.net says...
> As a memory designer for many years, this is up my alley.....
> A single transistor (and capacitor) may be used to store 1 bit
> of information - as in the case of a DRAM.
> (There is now a 1T SRAM cell but it's not yet in high
> production use).
The Nintendo GameCube uses 1T SRAM. I'd call that "high production
use".
> A standard
> SRAM will use six transistors to store 1 bit of information.
>
> Hence, to store 64 bits in DRAM - 64 transistors. In SRAM,
> 384 transistors. This accounts only for the storage cells and not the
> memory periphery logic.
Of course there are other memory types, as well. Some Flash
technologies can store more than one bit per cell. A ROM array may
have less than one (half) transistor per bit. It's indeed a tough
question to answer in such general terms.
--
Keith
normanstrong
Almost nothing. There are several LSI chips in instruments throughout
the world that have my name etched into the chip in a bare spot. If
it had been done with ROM, it would have taken less than 1% of the
area actually consumed.
Norm Strong
Robert Baer
64 transistors if you want to be wasteful, 32 if not (sero compression
or encoding).
Al Borowski
cheers,
Al