SOLVED Cores vs Threads

Hello guys...I know that this topic is boring....but I just want to know the basic difference between cores and threads. the i7 has 4 cores and 8 threads whereas the i5 has 4 cores and 4 threads. Take an example. Suppose a multithreaded program is being run on both i5 and i7 (both speeds 3Ghz). i5 will run the 4 threads at 3Ghz right?? but what about the i7? will it run 2 threads on each core, meaning will the threads run at 3Ghz each or will they run at 1.5Ghz each? Does a quad core with hyperthreading offer the same performace as a octa-core with no hyperthreading (assuming both are of the same architecture)?
Why aren't Intel making 8-core CPU's? Why are they sticking with 4 cores with hyperthreading?

the threads are all capable of maximum speed, but the hyper threaded cores will only be about 30% as efficient as a true core

Core = phsyical on the CPU 1 thread for each core. When you jump into a CPU that uses Hyperthreading, each core can now work on two threads simultaneously. As Dejo mentions, the threads run notably slower than the real core/thread, but it is still much faster than a non Hyperthreaded counterpart.