1978: data storage-board of the SM4
Main memories
The main memory is an important part in a computer-system, because it affords a faster access time for data and programms than for example a hard disk.
After early technics for main memories like diode- and valve plug-in units and magnetic tapes, a memory was needed that was fast, save and which worked without mechanical movements. The magnetic-core memory fulfilled all this characteristics. It also stores its data without electrical current. This main memory is such a magnetic-core memory. The cores are arranged in the noticeable rectangle with the little dark rectangles in it. One magnetic-core stores either '0' oder '1'. The cores are situated on the cross-ways of reading- and writing-wires, which run into the big rectangle from all sites. The storage occures with the aid of the direction of the remaining magnetism in the ring-cores after switching off the electrical current whereby the magnetic field vanishes.
To read out the data of a core, a voltage impulse must be induced on the reading-wire. A special characteristic is that the information are destroyed by this procedure. That's why they must be stored instantly again.
To design components more clearly, they were set on conductor plates since the 1950s, which serves the mechanical fixation as well as the electrical connection.
