Storage
Preliminary remark: Only the "static" semiconductor storage will be explained here (neither "mass storage" as e.g. hard disks, memory cards, USB-sticks nor the "dynamic" storage elements as they can be found as workspace in all modern computers). Also the programmable and other read-only memories which are essential to run a computer will be neglected here.
A problem keeping busy all calculating technicians:
How can a number, seeming worth to remember, be kept for later calculations? If I am not willing to memorize it, I could write it down as the most simple way. Mechanic calculators of the upper class could "back transfer" a result to the entrance. How can that be done electronically?
An electro-mechanic way seems easy: Every light switch has the desired property to keep a state (on/off) as long until I change it. "Flip-flop" the technician will say.
But how can it be done "the electronic way" - that means without mechanical parts - only electricity should do it? (Therefore the simple relay solutions will not be admitted - but in the following they may be used for explanation.)
Somehow we are urged to keep one of the dual states as long as desired - eventually until we switch off the apparatus. It should be "stored".
As before we will name these states as 0 and 1 (in the drawings by black and red) - but we could use, as mentioned before
take any other different pair of designations.
But in informatics the agreement about "0" and "1" (or "L" and "H") has been reached. In the computer there are two different voltages (indicated by the data sheet.
How can an - electric circuit, namely a 'logical' controlled one - be made to keep its state?
According to rising intrication we will distinguish three substantial solutions:
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