Digital and Analog Computers can be either digital or analog. Digital refers to the processes in computers that manipulate binary numbers (0s or 1s), which represent switches that are turned on or off by electrical current. Analog refers to numerical values that have a continuous range. Both 0 and 1 are analog numbers, but so is 1.5 or a number like p (approximately 3.14). As an example, consider a desk lamp.
If it has a simple on/off switch, then it is digital, because the lamp either produces light at a given moment or it does not. If a dimmer replaces the on/off switch, then the lamp is analog, because the amount of light can vary continuously from on to off and all intensities in between. Analog computer systems were the first type to be produced. A popular analog computer used in the 20th century was the slide rule. It performs calculations by sliding a narrow, gauged wooden strip inside a rulerlike holder. Because the sliding is continuous and there is no mechanism to stop at one exact value, the slide rule is analog. New interest has been shown recently in analog computers, particularly in areas such as neural networks that respond to continuous electrical signals. Most modern computers, however, are digital machines whose components have a finite number of states-for example, the 0 or 1, or on or off of bits. These bits can be combined to denote information such as numbers, letters, graphics, and program instructions. Range of Computer Ability Computers exist in a wide range of sizes and power. The smallest are embedded within the circuitry of appliances, such as televisions and wrist watches. These computers are typically preprogrammed for a specific task, such as tuning to a particular television frequency or keeping accurate time. Programmable computers vary enormously in their computational power, speed, memory, and physical size. The smallest of these computers can be held in one hand and are called personal digital assistants (PDAs). They are used as notepads, scheduling systems, and address books; if equipped with a cellular phone, they can connect to worldwide computer networks to exchange information regardless of location. Laptop computers and PCs are typically used in businesses and at home to communicate on computer networks, for word processing, to track finances, and to play games. They have large amounts of internal memory to store hundreds of programs and documents. They are equipped with a keyboard; a mouse, trackball, or other pointing device; and a video display monitor or liquid crystal display (LCD) to display information. Laptop computers usually have similar hardware and software as PCs, but they are more compact and have flat, lightweight LCDs instead of video display monitors. Workstations are similar to personal computers but have greater memory and more extensive mathematical abilities, and they are connected to other workstations or personal computers to exchange data. They are typically found in scientific, industrial, and business environments that require high levels of computational abilities. Mainframe computers have more memory, speed, and capabilities than workstations and are usually shared by multiple users through a series of interconnected computers. They control businesses and industrial facilities and are used for scientific research. The most powerful mainframe computers, called supercomputers, process complex and time-consuming calculations, such as those used to create weather predictions. They are used by the largest businesses, scientific institutions, and the military. Some supercomputers have many sets of CPUs. These computers break a task into small pieces, and each CPU processes a portion of the task to increase overall speed and efficiency. Such computers are called parallel processors.
