In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information. [...] Flip-flops and latches are used as data storage elements. Such data storage can be used for storage of state, and such a circuit is described as sequential logic.

Source: Flip-flop (electronics), Wikipedia

What are these states in Flip-flops?

I know that DRAM-storage makes use of capacitors. The two states are: Either the capacitor is charged or not. But I have no idea how to imagine the state of Flip-flops. What changes in the flip-flop if the state changes?

I am not a physicist, so please keep your answer as simple as possible.


A flip-flop (bistable multivibrator) is, in simple terms, two transistors wired together in such a way that there are two stable conditions: (1) one transistor is full "on", while the other if full "off" (2) vice versa

If the circuit happens to be in a state "in-between" these two states, it will, due to positive feedback, very rapidly move towards one of the stable states and remain there until power is removed or until it is forced into the other state via the inputs.

The outputs of the flip flop are taken from the transistors and are either "high" or "low" depending on whether the transistor is "off" or "on" respectively.

  • $\begingroup$ Wow... That's a very good answer! $\endgroup$ – Schrödinger's Cat Jul 7 '12 at 17:29

If you imagine a small loop lying on a surface, how many different directions can an electric current go within it?

The answer is two of course. With some pretzel-like shape changes, that's also what happens in a flip-flop: "flip" is (for example) a counter-clockwise current, and "flop" is a clockwise current (again, the shape is more like a pretzel though).

Because flip-flops are active currents, they take constant power to keep them on. That's why storing information in some other form such as charge (flash drives), magnetic fields held by tiny magnet regions (disk drives and tapes), or physically different "dots" (any form of optical storage) is always more efficient.

On the other hand, the flip-flop is very fast, since it's essentially constantly being "primed" with electrical current. That's why the registers and some forms of cache memory -- the very fastest form of storage in a computer chip -- are done using flip-flops, but not much else. Good use of hierarchies of slower and slower memories can make those very high speeds seem available much more broadly, since computer tend to go over the same small and local set of data many times before reaching out to slower storage devices.


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