Central Processing Unit and Input/Output

The above systems all share a dependence on components that allow the actual interaction between computer and users. These electronic components are categorized under two general headings: CPU and input /output (I /O) devices. Input devices transfer information from the designer into the computer’s CPU so that the data, encoded in binary sequencing, may be manipulated and analyzed efficiently. Output devices do exactly the opposite. They transfer binary data from the CPU back to the user in a usable (usually visual) format. Both types of devices are required in a CAD system. Without an input device, no information can be transferred to the CPU for processing, and without an output device, any information in the CPU is of little use to the designer because binary code is lengthy and tedious to interpret.

The main processing unit within the computer is known as the CPU, or microprocessor, or ‘‘processor’’ and handles all instructions and data. The difference between a microprocessor and a CPU is that a microprocessor can be the main processing chip in a computer as well as being any of the similar chips found in telephones or automobiles. The CPU, however, mostly refers only to the main processor and its related components within a computer.

Nevertheless, many people today use these two terms interchangeably. The make-up of the CPU chip is a tiny piece of silicon with an integrated circuit built on top of it. This whole unit then plugs into the computer’s motherboard and works together with several other components, such as the hard drive and memory area, to operate the data [a motherboard is the printed circuit board platform that typically houses the CPU, randomaccess memory (RAM), and expansion slots].

The inside of the CPU is made up of a variety of different components, each with a particular function. Some examples of these functions include a cache, a bus, a control unit, a decode unit, an FPU (floating-point unit), and an ALU (arithmetic logic unit). Connecting all of these components is a network of circuits and wires, some of which are no larger than 0.13 m in diameter, which is about one-thousandth the width of a human hair! To transfer the information, the CPU uses millions of electrical pulses per second to all of the different

components. Also contained within each CPU are millions of transistors that serve as the junction between the circuitry in the chip. To manipulate the data, these transistors either amplify or block the electrical pulses passing by. The calculations performed by the CPU can all take place on a chip no bigger than your thumbnail.

Many landmark events led to the creation of the CPU. First there was the creation of the transistor at Bell Labs in 1947, followed by the use of silicon to create transistors in 1954 at Texas Instruments. Then, at Texas Instruments and Fairchild Semiconductor, the first integrated circuit was created in 1958, all leading up to Intel’s creation of the 4004 microprocessor in 1971.

By today’s standards, the 4004 chip is meager compared to what is produced by Intel and AMD (Advanced Micro Devices), the leading manufacturers of CPUs. To clarify, modern CPUs run at speeds of around 2 GHz or more, while the 4004 chip ran at 108 kHz. That means the modern CPUs run about two thousand times faster than the 4004 did. Also, the 4004 chip only contained 2250 transistors, while the Pentium 4 CPU contains 42 million!

Devices such as floppy diskette drives, CD-ROM drives, printers, and LANs (local-area networks) are all a part of the information exchange with the CPU commonly known as ‘‘I /O.’’ Information in the I /O process is carried via buses such as USB (universal serial bus), FireWire /IEEE (Institute of Electrical and Electronic Engineers) 1394, and SCSI (small-computer system interface).

The process of transferring data from the CPU to the memory is seemingly similar to an I /O activity. However, it is typically not considered as such. A majority of modern processors utilize a dedicated memory subsystem. Within the CPU, different types of events are differentiated by control lines; among these different types of events are memory cycles, I /O cycles, or some other type of event. To coordinate the various amounts of data trying to pass through the buses, the supporting hardware controls the external I /O and internal memory as needed. Without this management, bus contention issues can arise, where two

devices attempt to use the same bus at the same time.

In its most elementary forms, I /O can be input only, output only, or both, though there are certainly many different types of I /Os. An example of an output-only channel would include turning on a status light to inform the user of the hard disk drive status. When it comes to input-only devices, voltage sensors on the power supply are good examples that can inform the processor if it is operating within the acceptable limits. I /O buses or devices that both send and receive signals from the computer are the most common and can include

the mouse, keyboard, hard drives, network cards, audio cards, and video cards.

Central Processing Unit and Input/Output

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