Decimal computers, computers which have a decimal architecture

Computer architecture

In computer science and engineering, computer architecture is the practical art of selecting and interconnecting hardware components to create computers that meet functional, performance and cost goals and the formal modelling of those systems....

, represent numbers and/or addresses in decimal

Decimal

The decimal numeral system has ten as its base. It is the numerical base most widely used by modern civilizations....

, and provide instructions to operate on those numbers and/or addresses directly; examples of encoding used are BCD

Binary-coded decimal

In computing and electronic systems, binary-coded decimal is a digital encoding method for numbers using decimal notation, with each decimal digit represented by its own binary sequence. In BCD, a numeral is usually represented by four bits which, in general, represent the decimal range 0 through 9...

, Excess-3

Excess-3

Excess-3 binary-coded decimal ' or Stibitz code, also called biased representation or Excess-N, is a complementary BCD code and numeral system it is used on some older computers that uses a pre-specified number N as a biasing value. It is a way to represent values with a balanced number of positive...

, two-out-of-five code

Two-out-of-five code

In telecommunication, a two-out-of-five code is an m of n code that provides exactly ten possible combinations, and thus is popular for representing decimal digits using five bits...

, ASCII

ASCII

The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...

, and EBCDIC

EBCDIC

Extended Binary Coded Decimal Interchange Code is an 8-bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems....

.

Many early computer

Computer

A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

s, for example the ENIAC

ENIAC

ENIAC was the first general-purpose electronic computer. It was a Turing-complete digital computer capable of being reprogrammed to solve a full range of computing problems....

, IBM 702

IBM 702

The IBM 702 was IBM's response to the UNIVAC—the first mainframe computer using magnetic tapes. Because these machines had less computational power than the IBM 701 and ERA 1103, which were favored for scientific computing, the 702 was aimed at business computing.The system used electrostatic...

, IBM 705, IBM 650

IBM 650

The IBM 650 was one of IBM’s early computers, and the world’s first mass-produced computer. It was announced in 1953, and over 2000 systems were produced between the first shipment in 1954 and its final manufacture in 1962...

, IBM 1401

IBM 1401

The IBM 1401 was a variable wordlength decimal computer that was announced by IBM on October 5, 1959. The first member of the highly successful IBM 1400 series, it was aimed at replacing electromechanical unit record equipment for processing data stored on punched cards...

, IBM 1620

IBM 1620

The IBM 1620 was announced by IBM on October 21, 1959, and marketed as an inexpensive "scientific computer". After a total production of about two thousand machines, it was withdrawn on November 19, 1970...

, IBM NORC

IBM NORC

The IBM Naval Ordnance Research Calculator was a one-of-a-kind first-generation electronic computer built by IBM for the United States Navy's Bureau of Ordnance. It went into service in December 1954 and was likely the most powerful computer at the time...

, IBM 7070

IBM 7070

IBM 7070 was a decimal architecture intermediate data processing system that was introduced by IBM in June 1960. It was part of the IBM 700/7000 series, and was based on discrete transistors rather than the vacuum tubes of the 1950s. It was the company's first transistorized stored-program...

, IBM 7080

IBM 7080

The IBM 7080 was a variable word length BCD transistor computer in the IBM 700/7000 series commercial architecture line, introduced in August 1961, that provided an upgrade path from the vacuum tube IBM 705 computer....

, Electrodata 200, UNIVAC I

UNIVAC I

The UNIVAC I was the first commercial computer produced in the United States. It was designed principally by J. Presper Eckert and John Mauchly, the inventors of the ENIAC...

, UNIVAC II

UNIVAC II

The UNIVAC II was an improvement to the UNIVAC I that UNIVAC first delivered in 1958. The improvements included core memory of 2000 to 10000 words, UNISERVO II tape drives which could use either the old UNIVAC I metal tapes or the new PET tapes, and some of the circuits were transistorized...

 and UNIVAC III

UNIVAC III

The UNIVAC III, designed as an improved transistorized replacement for the vacuum tube UNIVAC I and UNIVAC II computers, was introduced in June 1962. It was designed to be compatible for all data formats...

 used decimal arithmetic (IBM 1401 addresses were a combination of decimal and binary arithmetic). Some had a variable wordlength, which enabled operations on numbers with a large number of digits.

Later, several microprocessor

Microprocessor

A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

s offered limited decimal support. For example, the 80x86 family of microprocessors provide instructions to convert one-byte BCD

Binary-coded decimal

In computing and electronic systems, binary-coded decimal is a digital encoding method for numbers using decimal notation, with each decimal digit represented by its own binary sequence. In BCD, a numeral is usually represented by four bits which, in general, represent the decimal range 0 through 9...

 numbers (packed and unpacked) to binary format

Binary file

A binary file is a computer file which may contain any type of data, encoded in binary form for computer storage and processing purposes; for example, computer document files containing formatted text...

 before or after arithmetic operations
. These operations were not extended to wider formats and hence are now slower than using 32-bit

32-bit

The range of integer values that can be stored in 32 bits is 0 through 4,294,967,295. Hence, a processor with 32-bit memory addresses can directly access 4 GB of byte-addressable memory....

 or wider BCD 'tricks' to compute in BCD (see http://www.cs.uiowa.edu/~jones/bcd/bcd.html).

The 68000

Motorola 68000

The Motorola 68000 is a 16/32-bit CISC microprocessor core designed and marketed by Freescale Semiconductor...

 provided instructions for BCD addition and subtractions
, these instructions were removed when the Coldfire

Freescale ColdFire

The Freescale ColdFire is a microprocessor that derives from the Motorola 68000 family architecture, manufactured for embedded systems development by Freescale Semiconductor .-Instruction set:...

 instruction set was defined, and all IBM mainframes also provide BCD integer arithmetic in hardware.

Decimal arithmetic is now becoming more common; for instance, three decimal floating-point types with two encodings have been added to the new IEEE 754

IEEE 754r

The IEEE Standard for Floating-Point Arithmetic is a technical standard established by the Institute of Electrical and Electronics Engineers and the most widely used standard for floating-point computation, followed by many hardware and software implementations...

 standard, with 7, 16, and 34-digit decimal significand

Significand

The significand is part of a floating-point number, consisting of its significant digits. Depending on the interpretation of the exponent, the significand may represent an integer or a fraction.-Examples:...

s..

The IBM Power6 processor

POWER6

The POWER6 is a microprocessor developed by IBM that implemented the Power ISA v.2.03. When it became available in systems in 2007, it succeeded the POWER5+ as IBM's flagship Power microprocessor...

, the IBM System z9, and the IBM System z10

IBM System z10

IBM System z10 is a line of IBM mainframes. The z10 Enterprise Class was announced on February 26, 2008. On October 21, 2008, IBM announced the z10 Business Class , a scaled down version of the z10 EC...

 have implemented these types using the Densely Packed Decimal

Densely Packed Decimal

Densely packed decimal is a system of binary encoding for decimal digits.The traditional system of binary encoding for decimal digits, known as Binary-coded decimal , uses four bits to encode each digit, resulting in significant wastage of binary data bandwidth...

scheme for encoding the digits of the significand (binary encoding is used for the exponent)., the first and third in hardware and the second in microcode.