In this world, I have created a RAM and Register which uses locked redstone repeaters to hold information. This is not a fully assembled computer. It is very space efficient but is also time-consuming. It could be quite interesting for a redstone computer, especially ones which are to hold more than 8 bits of information.

Here's how it works:

At the time unit (third image), you can set the redstone lines to on or off by connecting the redstone. It is currently set to 11111000. Then stand on the pressure plate to set it to the register and then again to set the RAM to the register. Stepping on the pressure plate will make the RAM address selected output its information, to the receiver (the large unit with 8 redstone lamps) where it is changed from a single channel bus to an 8 channel bus. This RAM can store 8 bits and is meant to store more than 8 bits due to its compact size.

Change the RAM address by turning on/off the three green lines (second image). That is the Memory Address Register, Though not the most compact one. This will open a repeater which is connected to the single data bus and when the single set bus is on, will allow the RAM to be set.

The third component is the register, a bit to the right of the RAM. There are three blue lines. The bottom one opens the repeaters inside the register allowing it to be set, the middle one allows it to write to the bus in front of it and the top one allows it to write to the bus above it. You can set the bottom bus going into it with the given levers.

The final component is separated away from the RAM. That is the instruction memory. It is good for memorizing set instructions (set by the blue lapiz blocks, there are redstone torches underneath it). It can run without a program counter. It is 12 bit and each row can store one of 16 instructions and an 8 bit operand. This is set by the command blocks beside it. Just push the button.

Lights to the left of the instruction memory is to control flow. There are two SKIP levers which if both are on, if the light blue SKIP line is on, will not execute the instruction. The two REPEAT levers on for when the instruction repeats itself. The one STOP lever is on for when the instruction will stop (good for repeats). The orange TERMINATE line is on for when the instruction is to be terminated and stopped.

Hopefully, this is somewhat understandable and inspires an idea or two.