Williams tube

The system was adversely affected by nearby electrical fields, and required frequent adjustment to remain operational.

The resulting charge well remains on the surface of the tube for a fraction of a second while the electrons flow back to their original locations.

The process of creating the charge well is used as the write operation in a computer memory, storing a single binary digit, or bit.

This places an upper limit on the memory density, and each Williams tube could typically store about 256 to 2560 bits of data.

Typically, the computer would load the memory address as an X and Y pair into the driver circuitry and then trigger a time base generator that would sweep the selected locations, reading from or writing to the internal registers, normally implemented as flip-flops.

During the short period when the write takes place, the redistribution of charges in the phosphor creates an electrical current that induces voltage in any nearby conductors.

Those locations that were previously written to are already depleted of electrons, so no current flows, and no voltage appears on the plate.

Since the refresh process caused the same pattern to continually reappear on the display, there was a need to be able to erase previously written values.

[9][10] Tom Kilburn wrote a 17-instruction program to calculate the highest proper factor of numbers as large as 218.

By contrast, mercury delay-line memory was slower and not random access, as the bits were presented serially, which complicated programming.

Delay lines also needed hand tuning, but did not age as badly and enjoyed some success in early digital electronic computing despite their data rate, weight, cost, thermal and toxicity problems.