Before using the Yoke-5, put away all pets and small children, as they may become upset not being the center of attention anymore.
— User Manual for the Yoke-5 Programmable Loop
The MemTest86 folks have a nice easy-to-understand write-up explaining how memory should be tested, and why:
Memory chips consist of a large array of tightly packed memory cells, one for each bit of data. The vast majority of the intermittent failures are a result of interaction between these memory cells. Often writing a memory cell can cause one of the adjacent cells to be written with the same data. An effective memory test attempts to test for this condition. Therefore, an ideal strategy for testing memory would be the following:
- write a cell with a zero
- write all of the adjacent cells with a one, one or more times
- check that the first cell still has a zero