No, not all memory is created equal. As for determining compatibility, it's not always that easy. If one computer is a couple years older than the other, then it's unlikely they are compatible. Even being made at the same time does not guarantee compatibility. Determining compatibility is not easy. You need to determine the memory type, speed, size and parity to verify it is compatible with your current memory. Sometimes the memory is clearly labeled but usually not. Each memory manufacturer labels it in different ways so you might be able to determine it. Sometimes mixing memory between 2 manufacturer's is not compatible. Your PC may have special requirements too (e.g. always install as pairs or have largest memory first). By the way, largest does not mean more or less chips on the card. This is not something I would recommend for a novice. This not something that is easily accomplished, especially thru emails. If you have a friend who's familiar with this, then maybe you could get them to help you. In general, I've never seen permanent damage by using incompatible memory but there is a possibility it could do damage. Usually the card won't fit if it's the wrong type. If it's incompatible, then usually the machine won't boot or the memory won't show up. Removing the memory usually fixes the problem. If the memory is for a different voltage, then it may be damaged or no longer usable. If your not familiar with changing parts in your PC, then you should be careful. For instance, even though you unplug the PC, there could still be power stored in it. Your PC manual might tell you how to disipate this. All my PC's use the power switch. The power light turns on for a short burst. Also stay away from anything that could build up a static charge and ground yourself to the case at least before you touch any components otherwise you could damage them. Best it to remain permanent grounded. There are wristband connectors for this. In case of emergency, I have used an elbow on the case and contorted my arm.