A computer is a complex electronic machine, but its operations can be understood sufficiently in terms of a few interconnected components:
The processor is further divided into two smaller components
In the picture note that the components are connected through a set of wires called the bus.
The operations of any processor are as follows ad infinitum ("forever"):
This is called the fetch/execute cycle. Note that the processor is so much faster than the I/O devices, that I/O doesn't appear prominently here. A modern processor is able to execute millions of instructions while waiting for an I/O device, even a fast device like the disk or the network.
The main point here is that the computer doesn't know how to do anything "automatically": there's always some program code (set of instructions) telling it how to do something.
The input/output unit is connected with the usual peripherals such as keyboard, mouse, the various "drives" (such as hard drives, floppy drives, zip drives, DVD drives, CDROM drives, etc), monitors, printers etc. So, the components and operations of a computer are remarkably simple. Complication enters only for performance reasons, but any computer that you are likely to see these days contains the above components.
Looking at the picture above, you see a big yellow box
Memory, but you'll also see, if you look closely,
drive attached to the bus. What's the difference? Does it matter?
Yes, it does. The memory we describe there is super-fast memory chips that are right on the circuit board, just a few inches from the processor, what is sometimes called RAM or Random Access Memory. The most important properties of RAM are
If you've ever lost a document you were working on using your computer because the power went out or your battery ran out, that's because the stuff you were working on was in volatile memory. The files that are saved on the hard drive weren't lost.
The hard drive of your computer is (usually) a spinning disk with magnetic coating that stores the zeros and ones of your files as a pattern of magnetization. The exact representation isn't important, but two properties of hard drives are crucial:
There are other kinds of drives, such as solid-state drives, but the same properties appear. These properties mean that your computer mostly works by copying information (both programs and data, such as your files) from long-term storage on the hard drive into fast memory in the RAM, and that's where it stays while the computer is running. But you should save your stuff in RAM to hard disk on occasion, in order to avoid losing your work should someone trip on your power cord and pull the plug, or your battery unexpectedly die.
Finally, the most recent technology (invented in the past 15 years) is the USB flash drive , which has become the ubiquitous choice for transferring information between devices.