A lot of average computer user new to upgrading their computer power such as the CPU. For instant. A dell Alienware 51 motherboard will accept LGA 1366 socket CPU, and out there Intel has various CPU model with LGA 1366 sockets, so basically it will fit, but it’s not compatible.
So what will happen? basically a motherboard cpu socket is designed in a way that you can only fit certain CPU into the socket easily without any enormous force. So if it doesn’t fit perfectly then don’t force it, you might bend some of the pin either on the cpu unit or the cpu socket pin on the motherboard. However even though if it fit perfectly (Xeon LGA1366 vs. i7 920 LGA 1366) but doesn’t work when you turn it on then it’s probably not compatible, when you turn it on, basically no beep, no post beep, nothing, light on fan running that’s about it, nothing on screen. However need to know your motherboard is good and cpu is good lol 🙂
Rule of thumb, refer to your motherboard user manual if you have it to see which cpu is compatible, and check the cpu manual also, if you have it that is. If you don’t, try to contact the manufacturer, if not then ask computer guru forums, and last but probably not least, just try it on to the motherboard LOL and hope it doesn’t fried! 🙂