The hardware unit housing the CPU and main memory, among other things, is called the system unit.
The CPU has two main parts: the ALU (Arithmetic/Logic Unit) and the control unit. Arithmetic (e.g. addition) and logical (e.g. comparison) operations on data are performed in the ALU. Thus, the 'processing' of data performed by the computer is done in the ALU. Note that the ALU is capable of performing only very basic operations. Computers can do very 'complicated' things because they break the tasks up to great numbers of such basic operations and execute them at great speed. The control unit directs the flow of information within the computer's various components, including the I/O devices. Everything done by any component of the computer is the result of an order from the control unit.
Programs and data are stored in main memory while they are being processed. Each location in main memory into which an item of information can be stored has an address. The CPU 'knows' where to store/retrieve an information item in/from memory, because it has access to a table which contains the address for each item.
The electronic components making up the computer have a binary nature; there are two distinct voltage levels, circuits have two possible states (open or closed), a magnetized spot either exists or does not exist on a particular location on a diskette, etc. This suggests the usage of the binary number system in computers. A digit (either 0 or 1) in this system is called a bit ('binary digit'). All text characters (digits, letters, punctuation marks, etc.) entered (e.g. through the keyboard) or printed (e.g. via a printer) in/by the computer have to be converted to/from strings of bits which represent them within the computer. The two most popular character codes (i.e. lists of heavily-used characters and their associated bit strings) are ASCII (American Standard Code for Information Interchange) and EBCDIC. The computer system that you will be using in the PC labs uses the ASCII code. In that code, for instance, the letter 'A' is represented by the string/number 01000001 (i.e. decimal 65).
Since memory is composed of great numbers of 'components' which can store either a '0' or a '1', the bit can thought of as a unit of memory. The amount of memory used to represent a single character (usually 8 bits) is a byte. Other units of memory are, in increasing order, kilobyte (1 KB = 1024 bytes), megabyte (MB), gigabyte (GB), and terabyte (TB). A cheap PC may have 640 KB of main memory.
Program instructions which tell the computer what to do have to be translated to machine language (in which each instruction is a specific bit string) so that they can be executed by the control unit. As mentioned above, one high level language instruction is generally equivalent to several machine language instructions.
In addition to the control unit and the ALU, the CPU also contains several registers for storing the data processed by the instruction currently being executed, that instruction itself, and the addresses of data items and instructions that will be accessed. Think of the registers as a kind of memory which is much faster and much smaller than main memory.
The processing of a single machine language instruction is called a machine cycle. The machine cycle has two parts: the I-cycle in which the instruction is moved from the memory to the CPU and 'understood' by the CPU, and the E-cycle in which the act denoted by the instruction is actually carried out. (The E-cycle may involve more data transfer from the memory to the CPU.) Machine cycles in very fast computers can be measured in picoseconds!
The CPU's in most microcomputers are manufactured by one of two companies: Intel and Motorola. The PC's in our labs have Intel CPU's in them.
Most hardware components (e.g. CPU's or memory units) are manufactured by etching the related circuitry on silicon chips. Microcomputers are usually designed so that one can improve one's PC by incrementally buying and installing more chips with newer capabilities. Specialized processor chips (e.g. numeric or graphic coprocessors) which are supposed to work alongside the CPU chip are available. RAM (Random Access Memory) is another name for the chips which make up the main memory.
All the components of the computer are connected to the CPU via the bus; a set of 'wires' through which data and signals pass.
A 'classical' computer has a single CPU. Researchers who want to build even faster computers have come up with alternative 'architectures' in which there are two or more CPU's working in parallel. The main problems in this line of research are dividing the work to be done among the CPU's, and coordinating them so that they do not hinder but 'help' each other. This kind of computing is called parallel processing.