I learned at school that the clock rate inside a computer is the signal that keep switching between 0 - 1 (or active - inactive). There's also another delayed clock with the same frequency. These 2 clocks are then AND and OR together, and the out put is the enable-clock and set-clock.
When data is transferred inside the computer, it run from the original-register (inside the processing unit or on RAM) through the bus when the enable-clock is turned on, then set to its destination-register when set-clock = 1. Therefore, I thought that there's only 1 clock speed that run through the entire computer.
Back to the GPU, with its own processing unit and memory. Retailers' product pages always state 2 clock rates for a GPU: core clock and memory clock (which is several times faster than core clock). Which of those 2 clocks refer to the clock I've described above ? And what is the other clock.