36-bit computers were popular in the early
mainframe computer
A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterprise ...
era from the 1950s through the early 1970s.
Starting in the 1960s, but especially the 1970s, the introduction of 7-bit
ASCII
ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control c ...
and 8-bit
EBCDIC
Extended Binary Coded Decimal Interchange Code (EBCDIC; ) is an eight- bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems. It descended from the code used with punched cards and the corresponding si ...
led to the move to machines using
8-bit
In computer architecture, 8-bit integers or other data units are those that are 8 bits wide (1 octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers or data bu ...
bytes, with word sizes that were multiples of 8, notably the
32-bit
In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in a maximum of 32- bit units. Compared to smaller bit widths, 32-bit computers can perform la ...
IBM System/360
The IBM System/360 (S/360) is a family of mainframe computer systems announced by IBM on April 7, 1964, and delivered between 1965 and 1978. System/360 was the first family of computers designed to cover both commercial and scientific applicati ...
mainframe
A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterpris ...
and
Digital Equipment VAX and
Data General MV series superminicomputer
A superminicomputer, colloquially supermini, is a high-end minicomputer. The term is used to distinguish the emerging 32-bit architecture midrange computers introduced in the mid to late 1970s from the classical 16-bit systems that preceded them ...
s. By the mid-1970s the conversion was largely complete, and
microprocessor
A microprocessor is a computer processor (computing), processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, a ...
s quickly moved from 8-bit to 16-bit to 32-bit over a period of a decade. The number of 36-bit machines rapidly fell during this period, offered largely for
backward compatibility
In telecommunications and computing, backward compatibility (or backwards compatibility) is a property of an operating system, software, real-world product, or technology that allows for interoperability with an older legacy system, or with Input ...
purposes running
legacy programs.
History
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
A mechanical calculator, or calculating machine, is a mechanical device used to perform the basic operations of arithmetic automatically, or a simulation like an analog computer or a slide rule. Most mechanical calculators were comparable in si ...
, such as those manufactured by
Friden,
Marchant and
Monroe
Monroe or Monroes may refer to:
People and fictional characters
* Monroe (surname)
* Monroe (given name)
* James Monroe, 5th President of the United States
* Marilyn Monroe, actress and model
Places United States
* Monroe, Arkansas, an unincorp ...
. 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
The IBM 650 Magnetic Drum Data-Processing Machine is an early digital computer produced by IBM in the mid-1950s. It was the first mass-produced computer in the world. Almost 2,000 systems were produced, the last in 1962, and it was the firs ...
and the
IBM 7070, had a word length of ten digits, as did
ENIAC
ENIAC (; Electronic Numerical Integrator and Computer) was the first Computer programming, programmable, Electronics, electronic, general-purpose digital computer, completed in 1945. Other computers had some of these features, but ENIAC was ...
, one of the earliest computers.
Early binary computers aimed at the same market therefore often used a 36-
bit
The bit is the most basic unit of information in computing and digital communication. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represented as ...
word length
In computing, a word is any processor design's natural unit of data. A word is a fixed-sized datum handled as a unit by the instruction set or the hardware of the processor. The number of bits or digits in a word (the ''word size'', ''word wid ...
. This was 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 code
A six-bit character code is a character encoding 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 pun ...
. Computers with 36-bit words included the
MIT Lincoln Laboratory
The MIT Lincoln Laboratory, located in Lexington, Massachusetts, is a United States Department of Defense federally funded research and development center chartered to apply advanced technology to problems of national security. Research and dev ...
TX-2, the
IBM 701/704/709/7090/7094, the
UNIVAC 1103/
1103A/
1105 and
1100/2200 series, the
General Electric GE-600/
Honeywell 6000, the Digital Equipment Corporation
PDP-6
The PDP-6, short for Programmed Data Processor model 6, is a computer developed by Digital Equipment Corporation (DEC) during 1963 and first delivered in the summer of 1964. It was an expansion of DEC's existing 18-bit systems to use a 36-bit da ...
/
PDP-10
Digital Equipment Corporation (DEC)'s PDP-10, later marketed as the DECsystem-10, is a mainframe computer family manufactured beginning in 1966 and discontinued in 1983. 1970s models and beyond were marketed under the DECsystem-10 name, especi ...
(as used in the
DECsystem-10
Digital Equipment Corporation (DEC)'s PDP-10, later marketed as the DECsystem-10, is a mainframe computer family manufactured beginning in 1966 and discontinued in 1983. 1970s models and beyond were marketed under the DECsystem-10 name, especi ...
/
DECSYSTEM-20
The DECSYSTEM-20 was a family of 36-bit Digital Equipment Corporation PDP-10 mainframe computers running the TOPS-20 operating system and was introduced in 1977.
PDP-10 computers running the TOPS-10 operating system were labeled ''DECsystem ...
), and the
Symbolics 3600 series.
Smaller machines like the
PDP-1
The PDP-1 (Programmed Data Processor-1) is the first computer in Digital Equipment Corporation's PDP series and was first produced in 1959. It is known for being the most important computer in the creation of hacker culture at the Massachusetts ...
/
PDP-9
The PDP-9, the fourth of the five 18-bit minicomputers produced by Digital Equipment Corporation, was introduced in 1966. A total of 445 PDP-9 systems were produced, of which 40 were the compact, low-cost PDP-9/L units..
History
The 18-bit PDP ...
/
PDP-15
The PDP-15 was an 18-bit minicomputer by Digital Equipment Corporation that first shipped in February 1970. It was the fifth and last of DEC's 18-bit machines, a series that had started in December 1959 with the PDP-1. More than 400 were ordered ...
used
18-bit words, so a double word was 36 bits.
These computers had addresses 12 to 18 bits in length. The addresses referred to 36-bit words, so the computers were limited to addressing between 4,096 and 262,144 words (24,576 to 1,572,864 six-bit characters). The older 36-bit computers were 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
Memory segmentation is an operating system memory management technique of dividing a computer's primary memory into segments or sections. In a computer system using segmentation, a reference to a memory location includes a value that identifies ...
or other mechanisms.
The common character packings included:
* six 6-bit IBM
BCD or
Fieldata characters (ubiquitous in early usage)
* six 6-bit ASCII characters, supporting the upper-case unaccented letters, digits, space, and most ASCII punctuation characters. It was used on the PDP-6 and PDP-10 under the name
sixbit.
* six
DEC Radix-50 characters packed into 32 bits, plus four spare bits
* five 7-bit characters and 1 unused bit (the usual PDP-6/10 convention, called ''five-seven ASCII'')
[
* four 8-bit characters (7-bit ]ASCII
ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control c ...
plus 1 spare bit, or 8-bit EBCDIC
Extended Binary Coded Decimal Interchange Code (EBCDIC; ) is an eight- bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems. It descended from the code used with punched cards and the corresponding si ...
), plus four spare bits
* four 9-bit characters[
Marshall Cline]
"Would you please go over the rules about bytes, chars, and characters one more time?"
[
: "A file transfer protocol"
] (the Multics
Multics ("MULTiplexed Information and Computing Service") is an influential early time-sharing operating system based on the concept of a single-level memory.Dennis M. Ritchie, "The Evolution of the Unix Time-sharing System", Communications of t ...
convention).
Characters were extracted from words either using machine code
In computer programming, machine code is computer code consisting of machine language instructions, which are used to control a computer's central processing unit (CPU). For conventional binary computers, machine code is the binaryOn nonb ...
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 (''pronounced'' '' – like the letter c'') is a general-purpose programming language. It was created in the 1970s by Dennis Ritchie and remains very widely used and influential. By design, C's features cleanly reflect the capabilities of ...
requires that the size of the char
data type be at least 8 bits, and 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 char
s, although 12-bit, 18-bit, or 36-bit would also satisfy the requirements of the standard.
By the time IBM introduced System/360
The IBM System/360 (S/360) is a family of mainframe computer systems announced by IBM on April 7, 1964, and delivered between 1965 and 1978. System/360 was the first family of computers designed to cover both commercial and scientific applicati ...
with 32-bit
In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in a maximum of 32- bit units. Compared to smaller bit widths, 32-bit computers can perform la ...
full words, scientific calculations had largely shifted to floating point
In computing, floating-point arithmetic (FP) is arithmetic on subsets of real numbers formed by a ''significand'' (a signed sequence of a fixed number of digits in some base) multiplied by an integer power of that base.
Numbers of this form ...
, where double-precision formats offered more than 10-digit accuracy. 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 at least one line of 36-bit computer systems are still sold , the Unisys
Unisys Corporation is a global technology solutions company founded in 1986 and headquartered in Blue Bell, Pennsylvania. The company provides cloud, AI, digital workplace, logistics, and enterprise computing services.
History Founding
Unis ...
ClearPath Dorado series, which is the continuation of the 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 series continues to be supported today by Unisys Corporation as the ClearPath Dorado Serie ...
of mainframe computer
A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterprise ...
s.
CompuServe
CompuServe, Inc. (CompuServe Information Service, Inc., also known by its initialism CIS or later CSi) was an American Internet company that provided the first major commercial online service provider, online service. It opened in 1969 as a times ...
was launched using 36-bit PDP-10
Digital Equipment Corporation (DEC)'s PDP-10, later marketed as the DECsystem-10, is a mainframe computer family manufactured beginning in 1966 and discontinued in 1983. 1970s models and beyond were marketed under the DECsystem-10 name, especi ...
computers in the late 1960s. It continued using PDP-10
Digital Equipment Corporation (DEC)'s PDP-10, later marketed as the DECsystem-10, is a mainframe computer family manufactured beginning in 1966 and discontinued in 1983. 1970s models and beyond were marketed under the DECsystem-10 name, especi ...
and DECSYSTEM-10-compatible hardware and retired the service in the late 2000s.
Other uses in electronics
The LatticeECP3 FPGA
A field-programmable gate array (FPGA) is a type of configurable integrated circuit that can be repeatedly programmed after manufacturing. FPGAs are a subset of logic devices referred to as programmable logic devices (PLDs). They consist of a ...
s from Lattice Semiconductor include multiplier slices that can be configured to support the multiplication of two 36-bit numbers. The DSP block in Altera
Altera Corporation is a manufacturer of programmable logic devices (PLDs) headquartered in San Jose, California. It was founded in 1983 and acquired by Intel in 2015 before becoming independent once again in 2025 as a company focused on developm ...
Stratix FPGAs can do 36-bit additions and multiplications.
See also
* Physical Address Extension
In computing, Physical Address Extension (PAE), sometimes referred to as Page Address Extension,
is a memory management feature for the x86 architecture. PAE was first introduced by Intel in the Pentium Pro, and later by AMD in the Athlon process ...
(PAE)
* PSE-36 In computing, PSE-36 (36-bit Page Size Extension) refers to a feature of x86 processors that extends the physical memory addressing capabilities from 32 bits to 36 bits, allowing addressing to up to 64 GB of memory. Compared to the Physical Ad ...
(36-bit Page Size Extension)
* UTF-9 and UTF-18
References
{{CPU technologies
Data unit