Yes.
These are difficult to find but they do pop up on EBay occasionally. Search for "socket 775 cover" or "socket 775 protector" in "Computing".
Pentium 4s were available in Socket 423, Socket 478, and LGA 775.
Socket 775 (also known as LGA 775 or Socket T) is a socket for certain versions of the Intel Pentium 4, Celeron, Pentium D, Core Solo, Core Duo, Core 2 Duo, and Core 2 Quad. Unlike a traditional "socket", Socket 775 does not have any pinholes. instead, the pins are on the motherboard and reach up to contact the flat surface of the processor. Socket 775 was superseded by LGA 1156, but is still in common usage by most mainstream Core 2 Duo systems (as of January, 2010).
Correct.
No, it's not.
Depends on what socket you get. Each may be different. E.G: LGA 771 LGA 775 LGA 1366 Socket 478 Socket 939 Socket AM2 Socket AM2+ Socket AM3
Your question is very vague. The ASRock 945GCM only supports Socket 775 processors. So obviously the only comparison is that one with a Socket 775 processor installed will do something, and the other will not.
Depends on how much power you need. You use a Socket 775 processor for a socket 775 motherboard. Core 2 Quad @2.66Ghz, $169.99 Pentium Dual-Core @2.93Ghz, $79.99 The more power, the bigger the price.
The number 755 referes to the number of connections between the processor (CPU) and the socket that the CPU goes into. The number (and configuration) of connections between the CPU and the socket must be the same.
A used socket 775 motherboard is fairly hard to come by since they are moderately old in computing terms. However, by looking on auction sites such as eBay and selling sites such as Gumtree, one can find a used socket 775 motherboard relatively easily.
The socket 775 and the LGA 775 are the same. If you want to get technical it's not really a socket CPU, as the pins themselves are located on the socket grid and the back of the processor is flat with contact points. Totally opposite of what were used to seeing. Intel designed it this way to take increase the power distribution. The term LGA stands for Land Grid Array
Socket 478 is a processor socket used by certain versions of the Intel Pentium 4 and their Celeron counterparts. It consists of 478 contacts (pin holes) in a FC-PGA configuration. The Socket 478 format was replaced by the Socket 775 format.