This is my first post so tell me if I do something bad/annoying. Now for all the noobs out there; a clock circuit is a pulse in redstone wires. Like a flashing light going: tick, tick, tick. If you want to make a super fast one, you need at least a 3x3 block space. You need: x4 redstone dust,x1 lever & x4 redstone repeaters. On each border of the square on the middle, place a repeater and then connect then with the redstone. Place the lever next to one of the redstone wires and as fast as you can, flick it on and off. Break the lever and connect any redstone to one of the wires and connect that to and thing you want. (Despencers, pistons(not advised) droppers, doors etc.)
One step up is the hopper clock.All you need is two hoppers, any old item, and a comparator.Just put the hoppers facing eachother and put an item inside.Then you put a comparator facing one of the hoppers and connect redstone to that comparator.
The next fastest clock is the comparator clock.Set a comparator to subract mode and put a lever on the side with two torches.Then put redstone on the opposite side of the lever and on one sidd of the comparator, then connect the two peices of dust. Then you have the fastest ticking clock withot commands.The best part about this timmer is that you can turn it on and off.
You may want to reconsider pistons. http://www.mediafire.com/view/lemdsbg8lmhtul4/64-bytes-of-memory.jpg/file - all of those pistons in that image can fire in the same tick, even the ones that come after another one. You have to add repeaters to that to slow it down enough to see what's going on.In that image there are no empty spaces along those redstone lines, some of them just glitch out during each tick but still function. That's a 64 x 8-bit memory cell with instant read, instant write and separate read-write selectors that are also instant. Using those repeaters you can build a clock that has sub-tick resolution and pulses so rapidly it looks like it's always on. Feeding the pulses create by that clock causes a lot of other redstone evens to become instant (piston block movement, droppers, dispensers, etc).