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Dear
Dr. Universe,
How does a computer chip send information to the rest of the machine?
Chips range in size, with the largest now being a few centimeters on a side. Recently chips have grown in complexity and size, and are now nearly the size of a videocassette. Since whole circuits are manufactured at once, they are referred to as integrated circuits or ICs. In densely-packed ICs circuit elements may be only a few atoms in size. A typical computer circuit board features many integrated circuits connected together.
These sophisticated silicon chips are also known as a CPU or central processing unit. The Inted 8080 was the first microprocessor used in an affordable/home computer. The current Pentium 4 can run all code that ran on the 8080, but about 5,000 times faster. Processor chips typically contain many thousands of switches in the form of transistors and other parts. Pentium and later chips have over a million components. The microprocessor or CPU's function is to execute instructions of a program. The CPU brings data from the memory along a set of parallel wires called a bus (also known as a data bus). It then processes it by adding, subtracting, comparing, or performing some other simple operation and sends the results back to memory through the bus. The CPU has four major parts
1. Control unit (CU) which directs the flow of instructions and data and controls sequencing or operations.
2. Arithmetic and logic unit (ALU) which does simple operations on the data, such as adding, subtracting, and comparing.
3. Registers are memory locations which temporarily store data being processed by the ALU.
4. The clock is a crystal that vibrates millions of times per second. It times operations so that the CPU can keep in sequence.
Based on the instructions, a microprocessor or CPU does three basic things.
1. A microprocessor makes logical decisions which can result in the execution of new sets of instructions.
2. Using the ALC portion of the CPU a microporcessor performs addition, subtraction, multiplication, and division. Microprocessors can perform extremely sophisticated operations on large floating point numbers.
3. A microprocessor transfers data from one memory address to another.
In a typical operation, a signal from the clock causes the CU to fetch an instruction from a certain location in memory to the instruction register. The instruction might tell the CU to get a number from an area of data memory. The CU sets switches on the address bus to access the memory location and the current pulses representing the number flow from the memory along the data bus to the CPU where it is stored in a data register.
This process might be repeated for a second piece of data that is stored in a second data register. The next instruction might tell the ALU to add the two numbers and place the answer in the accumulator register. The next instruction would tell the CU to store the contents of the accumulator back into memory as a given address.
This sequence of fetch, fetch, process, store is a standard sequence of CPU operations. Just
about eveerything that happens in a computer flows through the CPU. The actual processing operations are always simple since the ALU cannot operate on more than two pieces of data at a time. But since the clock vibrates at several hundred megahertz to now beyond gigahertz the power of the computer is the speed at which it operates. Remember all these instructions and data are just thousands of switches opening and closing millions of times per second, which tends to boggle one's mind.
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