Anders Johansson wrote:
On Tuesday 19 July 2005 04:08, James Knott wrote:
Anders Johansson wrote:
Technically, a hard disk is non-volatile RAM, while internal memory is volatile RAM (meaning it gets cleared when you turn the power off) For many years, computers used non-volatile internal memory. It was called "core" memory.
I didn't know that, that is interesting. What was that based on? I'm guessing it wasn't based on the temporary flow of electricity, the way modern memory sticks are
It used tiny ferrite rings, which could be magnetized in either of two directions. The way they were read, was to erase a bit, and see if it changed polarity. Incidentally, this was referred to as "destructive read", in that you had to erase the data to read it. In core memory, there's the X & Y lines, to select the core you want to use, along with sense and inhibit lines. These two would run through all the cores in one bit plane. The when writing, the memory would try to set all the cores to one polarity, but the inhibit line, if enabled, would cancel that. Then on reading, the memory would try to force bit to the opposite polarity, and the sense line, would detect if the bit changed from one polarity to the other. Here's a brief description. http://www.science.uva.nl/faculteit/museum/CoreMemory.html