'Hello, World'. This first known 'Hello, world' from the seminal book originates from and in 1974. A computer program is a sequence of for performing a task designed to solve specific problems. Each program instruction is designed to be by a; computers require the capacity to execute programs in order to function. The instructions of a computer program are often specified by a. A computer programmer does this by means of the application of a. From the program in its human-readable form of, a can derive, which are computer program instructions that—as a result of being specified in a language that a computer can understand—are able to be directly executed by the computer they have been provided to.
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Alternatively, a computer program may be executed with the aid of an. The method applied by a computer to execute the instructions of a computer program is called an. A collection of computer programs,, and related are referred to as. Computer programs may be categorized along functional lines, such as and.
Lovelace's diagram from Note G, the In 1837, was inspired by Jacquard's loom to attempt to build the. The names of the components of the calculating device were borrowed from the textile industry.
In the textile industry, yarn was brought from the store to be milled. The device would have had a 'store'—memory to hold 1,000 numbers of 40 decimal digits each.
Numbers from the 'store' would then have then been transferred to the 'mill' (analogous to the CPU of a modern machine), for processing. It was programmed using two sets of perforated cards—one to direct the operation and the other for the input variables. However, after more than 17,000 pounds of the British government's money, the thousands of cogged wheels and gears never fully worked together.
During a nine-month period in 1842–43, translated the memoir of Italian mathematician. The memoir covered the Analytical Engine. The translation contained Note G which completely detailed a method for calculating using the Analytical Engine. This note is recognized by some historians as the world's first written computer program.
Universal Turing machine [ ] In 1936, introduced the —a theoretical device that can model every computation that can be performed on a computing machine. It is a that has an infinitely long read/write tape. The machine can move the tape back and forth, changing its contents as it performs an. The machine starts in the initial state, goes through a sequence of steps, and halts when it encounters the halt state. This machine is considered by some to be the origin of the —used by (1946) for the 'Electronic Computing Instrument' that now bears the name.
Early programmable computers [ ] The, invented by (1941) in, was a digital and programmable computer. A digital computer uses electricity as the calculating component.
The Z3 contained 2,400 relays to create the. The circuits provided a,, nine-instruction computer. Programming the Z3 was through a specially designed keyboard and. The (Fall 1945) was a, general-purpose computer that used 17,468 to create the. At its core, it was a series of wired together.
Its 40 units weighed 30 tons, occupied 1,800 square feet (167 m 2), and consumed $650 per hour () in electricity when idle. Programming the ENIAC took up to two months. Three function tables were on wheels and needed to be rolled to fixed function panels. Function tables were connected to function panels using heavy black cables. Each function table had 728 rotating knobs. Programming the ENIAC also involved setting some of the 3,000 switches. Debugging a program took a week.
The ENIAC featured. Different sets of accumulators could simultaneously work on different algorithms. It used for input and output, and it was controlled with a.
It ran for eight years, calculating hydrogen bomb parameters, predicting weather patterns, and producing firing tables to aim artillery guns. The (June 1948) was the first electronic. Programming transitioned away from moving cables and setting dials; instead, a computer program was stored in memory as numbers. It was limited to eight instruction types, and program steps were entered by switches. Later computers [ ]. Switches for manual input on a 3, manufactured in the mid-1970s Computers manufactured until the 1970s had front-panel switches for programming.
The computer program was written on paper for reference. An instruction was represented by a configuration of on/off settings. After setting the configuration, an execute button was pressed. This process was then repeated. Computer programs also were manually input via. After the medium was loaded, the starting address was set via switches and the execute button pressed.
In 1961, the was built specifically to be programmed in the language. The hardware featured circuits to ease the phase. In 1964, the was a line of six computers each having the same. The Model 30 was the smallest and least expensive. Customers could upgrade and retain the same. Each System/360 model featured. With operating system support, multiple programs could be in memory at once.
When one was waiting for, another could compute. Each model also could other computers. Customers could upgrade to the System/360 and retain their or application software. Computer programming [ ].
A computer program written in the imperative programming style Computer programs can be categorized by the used to produce them. Two of the main paradigms are and. Imperative languages [ ] Imperative programming languages specify a sequential using declarations, expressions, and statements: • A declaration couples a name to a – for example: var x: integer; • An expression yields a value – for example: 2 + 2 yields 4 • A statement might assign an expression to a variable or use the value of a variable to alter the program's – for example: x:= 2 + 2; if x = 4 then do_something(); One criticism of imperative languages is the side effect of an assignment statement on a class of variables called non-local variables.
Declarative languages [ ] Declarative programming languages describe what computation should be performed and not how to compute it. Declarative programs omit the and are considered sets of instructions. Two broad categories of declarative languages are and. The principle behind functional languages (like ) is to not allow, which makes it easier to reason about programs like mathematical functions. The principle behind logical languages (like ) is to define the problem to be solved – the goal – and leave the detailed solution to the Prolog system itself.
The goal is defined by providing a list of subgoals. Then each subgoal is defined by further providing a list of its subgoals, etc. If a path of subgoals fails to find a solution, then that subgoal is and another path is systematically attempted. Compilation and interpretation [ ] A computer program in the form of a, computer programming language is called. Source code may be converted into an by a or immediately with the aid of an.
Compilers are used to translate source code from a programming language into either. Object code needs further processing to become machine code, and machine code consists of the native instructions, ready for execution. Compiled computer programs are commonly referred to as executables, binary images, or simply as – a reference to the used to store the executable code. Interpreters are used to execute source code from a programming language line-by-line. The interpreter each and performs its behavior. One advantage of interpreters is that they can easily be extended to an. The programmer is presented with a prompt, and individual lines of code are typed in and performed immediately.
The main disadvantage of interpreters is computer programs run slower than when compiled. Interpreting code is slower because the interpreter must decode each statement and then perform it.
However, software development may be faster using an interpreter because testing is immediate when the compiling step is omitted. Another disadvantage of interpreters is an interpreter must be present on the executing computer. By contrast, compiled computer programs need no compiler present during execution.
Pre-compile computer programs just before execution. Avs Video Converter. For example, the Java Hotspot contains a Just In Time Compiler which selectively compiles Java bytecode into machine code - but only code which Hotspot predicts is likely to be used many times. Either compiled or interpreted programs might be executed in a without human interaction. Are often used to create batch processes. One common scripting language is, and its executing environment is called the. No properties of a programming language require it to be exclusively compiled or exclusively interpreted.