dual core processors?

what is parallel processing which is carried on in such systems?
which has more processing power- single core 4.0 ghz or dual core 2.0 ghz or ae both equally good?

While the outcome is usually correct it is a bit more complicated.

Basically, there are dozens or more 'threads' running on a system, these are also known as processes. A dual core processor (as stated) is 2 processors on 1 socket, closely aligned with each other. They can each handle all of the processes on a system, but they will split tasks between them. This is especially good for multitasking. But while running single programs that are not ported for dual core usage, it means that it will not make much of a difference at all as a 4 Ghz proc will run it faster. However, if the program can utilize multiple threads and/or is ported for dual core processors, then the speed gains are very good.

As for the other questions
Will programs still run -- Yes, most programs will still run because the program is unaware of the multiple processors. However, they may only use 1 of the 2 processors depending on how they were written.

The actual clock speed is 2.2 Ghz x2.It may seem faster because some of the processes will run on one processor, while others on the second. However, it is still running at 2.2 Ghz. The best advantage for dual core is when multitasking with several processor intensive programs. But many newer programs are starting to make use of multi-threading (using both processors at the same time to complete a task).

I hope this answers the questions well.