As we've talked about, there are lots of different components that all work together to make a computer work, but what is the basic flow of how all this gets done? Let's go through an example:
Let's assume the operating system is loaded and an application (let's say Mario Double Dash) is loaded onto the hard drive. When the user clicks on the Mario Double Dash icon an electronic signal is sent to the CPU to start up the game. The CPU then starts moving the application from the hard drive to DRAM. It does this because DRAM is much faster. It can't keep all the programs on DRAM because 1) there is usually a lot more memory on the hard disk drives and it wouldn't all fit and 2) the DRAM loses all it's memory when the power turns off.
Once Mario is loaded into the DRAM the CPU talks to the memory and starts running instructions. It grabs (fetches) one instruction at a time and executes it. On a basic level each instruction doesn't do a whole lot. An instruction tell the display controller to light a pixel on the screen or to move a byte of memory from one place to another. But altogether these instructions run very fast cause the game to run. All of these instructions together are called the program or application.
Now the CPU gets a lot of help in executing instructions. For example, in the case where a pixel needed to be set to a certain color, the CPU wouldn't actually send the signal to the screen to have this done, but would rather send an instruction to the Video chip or card and the video chip would then take that instruction and would connect to the monitor to tell it to turn on the pixel.
