2116 and other old memory chips

From: Vance Dereksen <vance_at_ikickass.org>
Date: Sat Jul 7 18:20:18 2001

Is that also why static RAM is so much faster?

Peace... Sridhar

On Sat, 7 Jul 2001, Tony Duell wrote:

> > This answers most of my questions, thanks. One further question. What
> > is the difference between "static" ram and "dynamic" ram, since both
> > are "volatile" ram? Or, putting it another way, what is "static" about
> > "static" ram, since it changes as well?
>
> OK...
>
> Static RAM is made from flip-flops. Which means that when you write data
> to it, you set some flip flops one way (for '1's) and some the other way
> (for '0's). And the flip-flops remain in that state until either you turn
> the power off or you write some other data to it.
>
> Dynamic RAM is made from capacitors. Generally, a '1' is represented by a
> charge on a capacitor, a '0' is a discharged capacitor. Writing data to
> DRAM involves charging some capacitors and discharging others.
>
> The problem is that all electronics has leakages. So the capacitors
> discharge themselves (in a few milliseconds). So you have to read each
> location periodically and write the data back again to 'refresh' the
> charge on the capacitors. Most (all?) DRAMs have internal circuitry to
> help with this (e.g. accessing a particular location will refresh a
> number of locations -- perhaps all those with the same pattern in the
> high-order half of the address). But you still have to do something -- on
> 'classic' DRAMs, you have to cycle the address inputs and apply RAS/
> pulses (or at least that's the normal way). If you don't, you lose data.
>
> That's the difference. The contents of static RAM are maintained as long
> as power is applied. Dynamic RAM needs to be refreshed or it will forget.
>
> -tony
>
Received on Sat Jul 07 2001 - 18:20:18 BST