what was parity ram? I once choose edo above normal ram for my 2nd pc, but cannot remember the use of parity ram anymore.
Parity RAM was RAM which had an extra check bit stored per byte of memory. This allowed the system to detect single-bit memory errors, and trigger a system halt. The reasoning being that it was better to halt the system than to (potentially) propagate corrupted data.
Parity RAM fell out of favor on consumer PCs for cost reasons, and because early versions of Windows were so buggy and unstable that errors caused by random "soft" memory errors were lost in the noise. And there was the whole "fake parity" scandal... look it up if you're interested in some good geeky history.
With the move to 64-bit wide DIMMs, it became possible to provide ECC (where single-bit errors are corrected transparently) for the same cost (in terms of additional DRAM bits) as parity -- current ECC DIMMs are 72 bits wide, with one additional ECC bit per byte. The ECC bits are calculated in a way that allows all single-bit errors to be corrected transparently, and most multi-bit errors to be at least detected. I was sorely disappointed that ECC did not become the norm; Intel decided to segment their product line by reserving ECC support for workstation/server class chipsets/CPUs. Most motherboard vendors opted not to implement ECC even for AMD systems, even though most AMD chipsets and CPUs have supported ECC since the original Athlon (some low-end Semprons and the newer APUs being notable exceptions to this). AMD ECC support is one of the reasons Asus remains at the top of my motherboard short list to this day.
If the world isn't making sense to you, you're either drinking too much or not drinking enough.