36-bit word length
Encyclopedia
Many early computers aimed at the scientific market had a 36-bit
word length. This word length was just long enough to represent positive and negative integers to an accuracy of ten decimal digits (35 bits would have been the minimum). It also allowed the storage of six alphanumeric characters encoded in a six-bit
character encoding
. Prior to the introduction of computers, the state of the art in precision scientific and engineering calculation was the ten-digit, electrically powered, mechanical calculator
, such as those manufactured by Friden
, Marchant
and Monroe
. These calculators had a column of keys for each digit and operators were trained to use all their fingers when entering numbers, so while some specialized calculators had more columns, ten was a practical limit. Computers, as the new competitor, had to match that accuracy. Decimal computers sold in that era, such as the IBM 650
and the IBM 7070
, had a word length of ten digits, as did ENIAC
, one of the earliest computers.
Computers with 36-bit words included the MIT Lincoln Laboratory
TX-2
, the IBM 701/704/709/7090/7094
, the UNIVAC
1103
/1103A/1105
/1100/2200
, the General Electric GE-600
/Honeywell 6000
, the Digital Equipment Corporation PDP-6
/PDP-10
(as used in the DECsystem-10/DECSYSTEM-20
), and the Symbolics 3600 series. Smaller machines like the PDP-1
/PDP-9/PDP-15 used 18-bit
words, so a double word would be 36 bits. EDSAC
had a similar scheme.
These computers used 18-bit word addressing, not byte addressing, giving an address space
of 218 36-bit words, approximately 1 megabyte of storage. Many of them were originally limited to a similar amount of physical memory as well. Architectures that survived evolved over time to support larger virtual address spaces using memory segmentation or other mechanisms.
The common character packings included
Characters were extracted from words either using machine code
shift and mask operations or with special-purpose hardware supporting 6-bit, 9-bit, or variable-length characters. The Univac 1100/2200 used the partial word designator of the instruction, the "J" field, to access characters. The GE-600 used special indirect words to access 6- and 9-bit characters; the PDP-6/10 had special instructions to access arbitrary-length byte fields.
The standard C programming language
requires that the size of the character data type be at least 8 bits, and that that all data types other than bitfields have a size that is a multiple of the character size, so standard C implementations on 36-bit machines would typically use 9-bit characters, although 12-bit, 18-bit, or 36-bit would also satisfy the requirements of the standard.
By the time IBM introduced System/360
, scientific calculations had shifted to floating point
and mechanical calculators were no longer a competitor. The 360s also included instructions for variable length decimal arithmetic for commercial applications, so the practice of using word lengths that were a power of two quickly became commonplace, though some 36-bit computer systems are still sold to this day, e.g., the Unisys
ClearPath series.
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
word length. This word length was just long enough to represent positive and negative integers to an accuracy of ten decimal digits (35 bits would have been the minimum). It also allowed the storage of six alphanumeric characters encoded in a six-bit
Sixbit
Six-bit character codes were designed for use on computers with word lengths a multiple of 6. Six bits can only encode 64 distinct characters, so these codes generally include only the upper-case letters, the numerals, some punctuation characters, and sometimes control characters...
character encoding
Character encoding
A character encoding system consists of a code that pairs each character from a given repertoire with something else, such as a sequence of natural numbers, octets or electrical pulses, in order to facilitate the transmission of data through telecommunication networks or storage of text in...
. Prior to the introduction of computers, the state of the art in precision scientific and engineering calculation was the ten-digit, electrically powered, mechanical calculator
Calculator
An electronic calculator is a small, portable, usually inexpensive electronic device used to perform the basic operations of arithmetic. Modern calculators are more portable than most computers, though most PDAs are comparable in size to handheld calculators.The first solid-state electronic...
, such as those manufactured by Friden
Friden, Inc.
Friden Calculating Machine Company was an American manufacturer of typewriters and electronic calculators. It was founded by Carl Friden in San Leandro, California in 1934. Friden electromechanical calculators were robust and popular....
, Marchant
Marchant Calculator
The Marchant Calculating Machine Co. was founded in 1911 by Rodney and Alfred Marchant in Oakland, California.The company built mechanical, and then electromechanical calculators which had a reputation for reliability. First models were similar to the Odhner arithmometer. In 1918, employee Carl...
and Monroe
Monroe Calculator Company
The Monroe Calculator Company was a leading maker of adding machines and calculators founded in 1912 by Jay R. Monroe and now known as Monroe Systems for Business...
. These calculators had a column of keys for each digit and operators were trained to use all their fingers when entering numbers, so while some specialized calculators had more columns, ten was a practical limit. Computers, as the new competitor, had to match that accuracy. Decimal computers sold in that era, such as the 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...
and the 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...
, had a word length of ten digits, as did 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....
, one of the earliest computers.
Computers with 36-bit words included the MIT Lincoln Laboratory
Lincoln Laboratory
MIT Lincoln Laboratory, located in Lexington, Massachusetts, is a United States Department of Defense research and development center chartered to apply advanced technology to problems of national security. Research and development activities focus on long-term technology development as well as...
TX-2
TX-2
The MIT Lincoln Laboratory TX-2 computer was the successor to the Lincoln TX-0 and was known for its role in advancing both artificial intelligence and human-computer interaction.- Specifications :...
, the IBM 701/704/709/7090/7094
IBM 700/7000 series
The IBM 700/7000 series was a series of large-scale computer systems made by IBM through the 1950s and early 1960s. The series included several different, incompatible processor architectures. The 700s used vacuum tube logic and were made obsolete by the introduction of the transistorized 7000s...
, the UNIVAC
UNIVAC
UNIVAC is the name of a business unit and division of the Remington Rand company formed by the 1950 purchase of the Eckert-Mauchly Computer Corporation, founded four years earlier by ENIAC inventors J. Presper Eckert and John Mauchly, and the associated line of computers which continues to this day...
1103
UNIVAC 1103
The UNIVAC 1103 or ERA 1103, a successor to the UNIVAC 1101, was a computer system designed by Engineering Research Associates and built by the Remington Rand corporation in October, 1953...
/1103A/1105
UNIVAC 1105
The UNIVAC 1105 was a follow-on computer to the UNIVAC 1103A introduced by Sperry Rand in September, 1958.The UNIVAC 1105 had either 8,192 or 12,288 words of 36 bit magnetic core memory, in two or three banks of 4,096 words each. Magnetic drum memory provided either 16,384 or 32,768 words, in one...
/1100/2200
UNIVAC 1100/2200 series
The UNIVAC 1100/2200 series is a series of compatible 36-bit computer systems, beginning with the UNIVAC 1107 in 1962, initially made by Sperry Rand...
, the General Electric GE-600
GE-600 series
The GE-600 series was a family of 36-bit mainframe computers originating in the 1960s, built by General Electric . When GE left the mainframe business the line was sold to Honeywell, who built similar systems into the 1990s as the division moved to Groupe Bull and then NEC.-Architecture:The 600...
/Honeywell 6000
Honeywell 6000 series
In 1970 General Electric sold their computing division to Honeywell. GE's 600-series machines were renamed as the Honeywell 6000 series and sold for a number of years.For complete details, see the GE-600 series entry....
, the Digital Equipment Corporation PDP-6
PDP-6
The PDP-6 was a computer model developed by Digital Equipment Corporation in 1963. It was influential primarily as the prototype for the later PDP-10; the instruction sets of the two machines are almost identical.The PDP-6 was DEC's first "big" machine...
/PDP-10
PDP-10
The PDP-10 was a mainframe computer family manufactured by Digital Equipment Corporation from the late 1960s on; the name stands for "Programmed Data Processor model 10". The first model was delivered in 1966...
(as used in the DECsystem-10/DECSYSTEM-20
DECSYSTEM-20
The DECSYSTEM-20 was a 36-bit Digital Equipment Corporation PDP-10 mainframe computer running the TOPS-20 operating system.PDP-10 computers running the TOPS-10 operating system were labeled DECsystem-10 as a way of differentiating them from the PDP-11...
), and the Symbolics 3600 series. Smaller machines like the PDP-1
PDP-1
The PDP-1 was the first computer in Digital Equipment Corporation's PDP series and was first produced in 1960. It is famous for being the computer most important in the creation of hacker culture at MIT, BBN and elsewhere...
/PDP-9/PDP-15 used 18-bit
18-bit
18 binary digits have unique combinations.-Example 18-bit computer architectures:* Possibly the most well-known 18-bit computer architectures are the PDP-1, PDP-4, PDP-7, PDP-9 and PDP-15 minicomputers produced by Digital Equipment Corporation from 1960 to 1975.* UNIVAC produced a number of...
words, so a double word would be 36 bits. EDSAC
EDSAC
Electronic Delay Storage Automatic Calculator was an early British computer. The machine, having been inspired by John von Neumann's seminal First Draft of a Report on the EDVAC, was constructed by Maurice Wilkes and his team at the University of Cambridge Mathematical Laboratory in England...
had a similar scheme.
These computers used 18-bit word addressing, not byte addressing, giving an address space
Address space
In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity.- Overview :...
of 218 36-bit words, approximately 1 megabyte of storage. Many of them were originally limited to a similar amount of physical memory as well. Architectures that survived evolved over time to support larger virtual address spaces using memory segmentation or other mechanisms.
The common character packings included
- six 5.32-bit DEC Radix-50 characters, plus four spare bits
- six 6-bit FieldataFieldataFieldata was a pioneering computer project run by the US Army Signal Corps in the late 1950s that intended to create a single standard for collecting and distributing battlefield information...
or IBM BCD characters (ubiquitous in early usage) - five 7-bit characters and 1 unused bit (the usual PDP-6/10 convention, called five-seven ASCII)
- four 8-bit characters (7-bit ASCIIASCIIThe 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...
plus 1 spare bit, or 8-bit EBCDICEBCDICExtended Binary Coded Decimal Interchange Code is an 8-bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems....
), plus four spare bits - four 9-bit characters (the MulticsMulticsMultics was an influential early time-sharing operating system. The project was started in 1964 in Cambridge, Massachusetts...
convention).
Characters were extracted from words either using machine code
Machine code
Machine code or machine language is a system of impartible instructions executed directly by a computer's central processing unit. Each instruction performs a very specific task, typically either an operation on a unit of data Machine code or machine language is a system of impartible instructions...
shift and mask operations or with special-purpose hardware supporting 6-bit, 9-bit, or variable-length characters. The Univac 1100/2200 used the partial word designator of the instruction, the "J" field, to access characters. The GE-600 used special indirect words to access 6- and 9-bit characters; the PDP-6/10 had special instructions to access arbitrary-length byte fields.
The standard C programming language
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
requires that the size of the character data type be at least 8 bits, and that that all data types other than bitfields have a size that is a multiple of the character size, so standard C implementations on 36-bit machines would typically use 9-bit characters, although 12-bit, 18-bit, or 36-bit would also satisfy the requirements of the standard.
By the time IBM introduced System/360
System/360
The IBM System/360 was a mainframe computer system family first announced by IBM on April 7, 1964, and sold between 1964 and 1978. It was the first family of computers designed to cover the complete range of applications, from small to large, both commercial and scientific...
, scientific calculations had shifted to floating point
Floating point
In computing, floating point describes a method of representing real numbers in a way that can support a wide range of values. Numbers are, in general, represented approximately to a fixed number of significant digits and scaled using an exponent. The base for the scaling is normally 2, 10 or 16...
and mechanical calculators were no longer a competitor. The 360s also included instructions for variable length decimal arithmetic for commercial applications, so the practice of using word lengths that were a power of two quickly became commonplace, though some 36-bit computer systems are still sold to this day, e.g., the Unisys
Unisys
Unisys Corporation , headquartered in Blue Bell, Pennsylvania, United States, and incorporated in Delaware, is a long established business whose core products now involves computing and networking.-History:...
ClearPath series.