Central processing unit

A central processing unit (CPU) refers to part of a computer that interprets and carries out, or processes, instructions and data contained in the software. The more generic term processor can be used to refer to a CPU as well; see processor (disambiguation) for other uses of this term. Microprocessors are CPUs that are manufactured on integrated circuits, often as a single-chip package. Since the mid-1970s, these single-chip microprocessors have become the most common and prominent implementations of CPUs, and today the term is almost always applied to this form.

History

Prior to the advent of machines that resemble today's CPUs, computers such as ENIAC had to be physically rewired in order to perform different tasks. These machines are often referred to as "fixed program computers" since they had to be physically reconfigured in order to run a different program. The earliest devices that could rightly be called CPUs came with the advent of the stored program computer. The idea of a stored program computer was already present during the design of ENIAC, but was not used in that computer due to speed considerations. Before ENIAC was even completed, on 1945-06-30 mathematician John Von Neumann published the paper entitled First Draft of a Report on the EDVAC, which outlined the design of a stored program computer that would eventually be completed in August 1949. EDVAC was designed to perform a certain number of instructions (or operations) of various types. These instructions could be combined to create useful programs for the EDVAC to run. Significantly, the programs written for EDVAC were stored in high speed computer memory, rather than being specified by the physical wiring of the computer. This overcame a severe limitation of ENIAC, which was the large amount of time and effort it took to reconfigure the computer to perform a new task. With Von Neumann's design, the program, or software, that EDVAC ran could be changed simply by changing the contents of the computer's memory.

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It should be noted that while Von Neumann is most often credited with the design of the stored program computer due to his design of EDVAC, others before him such as Konrad Zuse had suggested similar ideas. Additionally, the so-called Harvard architecture of the Harvard Mark I, which was completed before EDVAC, also utilized a stored-program design using punched paper tape rather than electronic memory. The key difference between the Von Neumann and Harvard architectures is that the latter separates the storage and treatment of CPU instructions and data, while the former uses the same memory space for both. Most modern CPUs are primarily Von Neumann in design, but elements of the Harvard architecture are commonly seen as well.

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Discrete component transistor CPUs

The design and complexity of CPUs increased as various technologies facilitated building smaller and more reliable electronic devices. The first such improvement came with the advent of the transistor. Transistorized CPUs during the 1950s and 1960s no longer had to be built out of bulky, unreliable, and fragile switching elements like vacuum tubes and electrical relays. With this improvement, more complex and reliable CPUs were built onto one or several printed circuit boards containing discrete transistor components. In 1964, IBM introduced its System/360 computer architecture, which was used in a series of computers that could run the same programs with different speed and performance. This was significant at a time when most electronic computers were incompatible with one another, even those made by the same manufacturer. To facilitate this improvement, IBM utilized the concept of a microprogram, which still sees widespread usage in modern CPUs (often called "microcode"). The System/360 architecture was so popular that it dominated the mainframe computer market for the next few decades and left a legacy that is still continued by similar modern computers like the IBM zSeries. In the same year (1964), Digital Equipment Corporation (DEC) introduced another influential computer aimed at the scientific and research markets, the PDP-8.

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Microprocessors

The most recent technological improvement that has affected the design and implementation of CPUs came in the mid-1970s with the microprocessor. Since the introduction of the first microprocessor (the Intel 4004) in 1970 and the first widely-used microprocessor (the Intel 8080) in 1974, this class of CPUs has almost completely overtaken all other implementations. While the previous generation of CPUs was integrated as discrete components on one or more circuit boards, microprocessors are manufactured onto compact integrated circuits (ICs), often a single chip. As the ability to construct exceedingly small transistors on an IC has increased, the complexity of and number of transistors in a single CPU has increased dramatically. This trend has been observed by many and is often described by Moore's law, which has proven to be a fairly accurate model of the growth of CPU (and other IC) complexity to date.

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While the complexity, size, construction, and general form of CPUs has changed drastically over the past sixty years, it is notable that the basic design and function has not changed much at all. Almost all common CPUs today are still very accurately described as Von Neumann stored program machines. As the aforementioned Moore's law continues to hold true, concerns about the limits of integrated circuit transistor technology have become much more prevalent, causing researchers to investigate new methods of computing such as the quantum computer as well as expand the usage of parallelism and other methods that extend the usefulness of the classical Von Neumann model.

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Computer: A computer is a device or for processing information from data according to a program — a compiled list of instructions. The information to be processed may represent numbers, text, pictures, or sound, amongst many other types....

Software: redirect Computer software...

Processor (disambiguation): A processor is mostly a central processing unit. It, however, can mean:...

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