ALi-B

iTrader: (1)

Tricky this. We need to go back to the physical fundamental and the individual components that are used to make each RAM bit; namely transistors and capacitors. Yes modern RAM is all built into a chip, but these chips house billions upon billions of them

In teh old days, static RAM is made up by transistors wired as such to make up a S-R flip-flop, which in turn makes up one bit of RAM. They are on or off depending on what operation is being done or what bit state is being stored. DRAM uses different method to hold bit states, and require refreshing, but its still is made up a of transitors of which their current consumption is dependant on the stored state.

To hold a "1" state does need a tiny amount more current flow than a "0" state. A "1" is line voltage (depending on design: 1.5v, 3.3v or whatever phones use, 5v for TTL etc. ), to hold that voltage does require a very small amount of current to keep the transistors within the chip biased (SRAM) and restore voltage within the capcitors (DRAM). Certinaly from old-school RAM, holding "11111111" takes more current that holding "00000000". But we're talking microamps here.

Also changing state require a small amount of power, as does refreshing the RAM, where each memory address has its stored state refeshed to keep it reliable. Due to nature of the chip's design, a "bit" may change state from voltage float, current leakage or interferance.

JAutos

iTrader: (5)

sounds interesting, i too am now keen to know, but i think your wrong as im led to beleive that the more work the ram is doing the more power it uses, kinda like if your doing 50mph in 5th on the motorway you will use less petrol than doing 125mph in 5th as more work means more power.

ALi-B

iTrader: (1)

I said changing bit state requires power too.

"Work" is exacty that; changing bit states, and holding bit states. If the bit state isn't expected to change, then consumption can be reduced (i.e in standby).

The fundamental thing here is a transistor to give a "1" output has to consume more current than a "0", be it to keep its state, or refresh a capacitor. If the memory is holding a word with lots of "1"s then it will consume more current. As a "1" data bit requires a higher voltage. Obviously an empty memory bank would be just a zero word, even so it still needs to be refreshed to ensure it stays that way - this will use current.

Consumption will also depend on the actual word stored, word being the physical number stored: For example "11111111" (FFh or 255 in decidmal) uses more current that "00000000" (00h, or 0 in decimal ). In between we have "01111111" (7Fh or 127 in decimal) which uses more current than "10000000" (80h or 128 in decimal).

Obviously, there is power saving stuff that plays a a part; Sleep mode would lower the refresh rate. If what is being stored doesn't need to change (like during sleep mode) then the refresh rate can be safely lowered without suffering corruption.

ALi-B

iTrader: (1)

I can't answer that; would need to know the specs of the RAM chips used.

Would be intresting to find out typical values though.