Buying RAM

When buying memory modules, forgetting a little detail quickly spoils the fun. So I made myself a checklist of points to consider:

PC3-6400 / DDR3-800 PC3-8500 / DDR3-1066 PC3-10600 / DDR3-1333 (sometimes PC3-10700) PC3-12800 / DDR3-1600
 * Generation: DDR3, DDR4, etc.
 * Size: DIMM or SO-DIMM. SO-DIMM modules tend to have an S suffix like in PC3L-12800S.
 * Whether it is labelled as "AMD only", which is often the case for DDR2.
 * ECC vs non-ECC PC3-10600 vs PC3-10600E Only "workstation class" motherboards tend to support ECC.
 * Registered / buffered  vs   non-registered / unbuffered PC3-10600R vs PC3-10600U Only "server class" motherboards tend to support registered modules.
 * Voltage: The DDR3L standard uses 1.35 V (instead of 1.5 V) and is labelled PC3L. Some modules support both voltages and are labelled as "dual voltage".
 * Speed: Some old PCs do not like faster modules, probably because the BIOS cannot handle faster values in the JEDEC timings table. Such a limitation is often out of economic motivation.
 * Where it comes from, in case customs duty applies.