Gianmario.Scotti_at_nokia.com
Date: 2003-06-16 11:12:58
Hi,
just wanted to chime in on SRAM vs. DRAM: SRAM is much faster, for reasons that are not simple to explain, but boil down to the fact that DRAM needs a special read access sequence, more complex than the one for SRAM. That's why cache memory is SRAM.
As for consumption, well, that depends. On one hand, fast SRAM memory, like the one used for cache RAM, is highly energy-consuming, because in order to have fast access times, relatively high currents in the flip-flop branches are necessary (higher current -> faster parasite capacitance discharge -> quicker writes & faster access). On the other hand, SRAM can be made also very energy-efficient, so it can be used for NVRAM. Take those Dallas NVRAM chips for example: they can maintain data for more than a decade. NVRAM is battery-backed SRAM.
So does SRAM consume less power than DRAM? Funnily enough, each expert seems to hold a different opinion on the subject, but my personal experience seems to indicate that SRAM consumes less energy than DRAM of comparable transistor technology and speed.
just my two cents of an euron
mario
P.S. This is my first post in cbm-hackers. I always top-post. Is that considered very rude here?
-----Original Message-----
From: ext Spiro Trikaliotis [mailto:trik-news@gmx.de]
Sent: 16. June 2003 11:19
To: cbm-hackers@cling.gu.se
Subject: Re: Reset Memory Pattern
Hello,
sorry for replying so late, but my internet broke on Friday. :-(
On Fri, Jun 13, 2003 at 10:07:41PM +0200, Gideon Zweijtzer wrote:
> No. SRAM is not made of flip-flops. This would take up a huge amount of
> silicon area, because a flip-flop is made of two latches, which are each
> made up out of two gates (and a 2-input CMOS gate is at least 4
> transistors). Traditional SRAM cells are made up of only 6 transistors,
> but I have heard that newer SRAM cells are made out of 2 or 4
> transistors only.
From my (analog) electronics days, I remember that there is an analog FF
consisting of only 2 transisters (bipolar, I have to admit). Do I understand
you wrong, or don't you like it to call some analog circuitry a FF?
> back after raising the power back to its nominal value.] SRAM is very
> low-power though, because the active loop is static and does not consume
> power, other than some leakage. Leakage is very small, because when the
> level of the SRAM cell does not change, there is just some charge kept
> on the insulated gate of the transistors.
Hm, well. This might be right with CMOS-SRAMs nowadays. Anyway, I doubt a
TTL-SRAM (or, even better, ECL-SRAM ;-)) having less power consumption than
a DRAM. Even with PMOS- or NMOS-SRAM, I don't think that it takes less power
than a DRAM.
Spiro.
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