This slows the machine down because it now takes longer to access memory. Generally, this option can be set to Zero, One, or Two wait states. The higher the number, the longer it waits between memory cycles. In addition, try to keep the same speed of RAM installed in your computer. If you have to mix speeds, make sure that you have the same speed RAM installed in each Bank.
Banks are usually sets of four memory chips on the motherboard.
Supporting hardware, like video cards, can often cause parity errors. The best way test this is to replace the device with one that is working correctly. Also faulty power supplies can cause parity errors. Odd and Even. The Parity BIT is set on or off depending on the count of ON bits, or 1's, in the data, usually a byte.