In computer architecture, 18-bit integers, memory addresses, or other data units are those that are 18 bits (2.25 octets) wide. Also, 18-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size.

18 binary digits have 262144 (1000000 octal, 40000 hexadecimal) distinct combinations.

18 bits was a common word size for smaller computers in the 1960s, when large computers often used 36 bit words and 6-bit character sets were the norm.

Example 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.

The UNIVAC produced several 18-bit computers, including the UNIVAC 418 and several military systems.

The IBM 7700 Data Acquisition System was announced by IBM on December 2, 1963.

The BCL Molecular 18 was a group of systems designed and manufactured in the UK in the 1970s and 1980s.

The NASA Standard Spacecraft Computer NSSC-1 was developed as a standard component for the MultiMission Modular Spacecraft at the Goddard Space Flight Center (GSFC) in 1974.

The flying-spot store digital memory in the first experimental electronic switching systems used nine plates of optical memory that were read and written two bits at a time, producing a word size of 18 bits.

Character encoding

18-bit machines use a variety of character encodings.

The DEC Radix-50, called Radix 508 format, packs three characters plus two bits in each 18-bit word.[1]

The Teletype packs three characters in each 18-bit word; each character a 5-bit Baudot code and an upper-case bit.[2]

The DEC SIXBIT format packs three characters in each 18-bit word,[2] each 6-bit character obtained by stripping the high bits from the 7-bit ASCII code, which folds lowercase to uppercase letters.


  1. ^ "Linking Loader". PDP-9 Utility Programs--Advanced Software System--Programmer's Reference Manual (PDF). Maynard, Massachusetts: Digital Equipment Corporation. 1968. p. A1-1. Archived (PDF) from the original on January 25, 2019.
  2. ^ a b PDP-7 Symbolic Assembler Programming Manual (PDF). Maynard, Massachusetts: Digital Equipment Corporation. 1965. pp. 6, 38–39. Archived (PDF) from the original on May 23, 2017.

In computer architecture, 36-bit integers, memory addresses, or other data units are those that are 36 bits (six six-bit characters) wide. Also, 36-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size.

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.

Early binary computers aimed at the same market therefore often used a 36-bit word length. 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. Computers with 36-bit words included the MIT Lincoln Laboratory 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/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 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 or other mechanisms.

The common character packings included:

six 5.32-bit DEC Radix-50 characters, plus four spare bits

six 6-bit Fieldata or IBM BCD 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.

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 plus 1 spare bit, or 8-bit EBCDIC), plus four spare bits

four 9-bit characters (the Multics convention).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 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 chars, although 12-bit, 18-bit, or 36-bit would also satisfy the requirements of the standard.By the time IBM introduced System/360 with 32-bit full words, scientific calculations had largely shifted to floating point, 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 as of 2019, the Unisys ClearPath Dorado series, which is the continuation of the UNIVAC 1100/2200 series of mainframe computers.

CompuServe was launched using 36-bit PDP-10 computers in the late 1960s. It continued using PDP-10 and DECSYSTEM-10-compatible hardware and retired the service in the late 2000s.

Amiga Advanced Graphics Architecture

Amiga Advanced Graphics Architecture (AGA) is the third-generation Amiga graphic chipset, first used in the Amiga 4000 in 1992. Before release AGA was codenamed Pandora by Commodore International.

AGA was originally called AA for Advanced Architecture in the United States. The name was later changed to AGA for the European market to reflect that it largely improved the graphical subsystem, and to avoid trademark issues.AGA is able to display graphics modes with a depth of up to 8 bits per pixel. This allows for 256 colors in indexed display modes and 262,144 colors (18-bit) in Hold-And-Modify (HAM-8) modes. The palette for the AGA chipset has 256 entries from 16,777,216 colors (24-bit), whereas previous chipsets, the Amiga Original Chip Set (OCS) and Amiga Enhanced Chip Set (ECS), only allowed 32 colors out of 4096 (64 colors in Amiga Extra Half-Brite (EHB mode)). Other features added to AGA over ECS were super-hi-res smooth scrolling and 32-bit fast page memory fetches to supply the graphics data bandwidth for 8 bitplane graphics modes and wider sprites.

AGA was an incremental upgrade, rather than the dramatic upgrade of the other chipset that Commodore had begun in 1988, the Amiga Advanced Architecture chipset (AAA), lacking many features that would have made it competitive with other graphic chipsets of its time. Apart from the graphics data fetches, AGA still operates on 16-bit data only, meaning that a lot of bandwidth is wasted during register accesses and Amiga 'copper' and blitter operations. Also the lack of a chunky graphics mode is a speed impediment to graphics operations not tailored for planar modes, resulting in ghost artifacts during the common productivity task of scrolling. In practice, the AGA HAM mode is mainly useful in painting programs, picture viewers and for video playback. Workbench in 256 colors is much slower than ECS operation modes for normal application use; a workaround is to use multiple screens with different color depths. AGA lacks flicker free higher resolution modes, being only able to display 640 × 480 at 72 Hz flicker-free operation. 800 × 600 mode is rarely used as it can only operate at a flickering 60 Hz interlaced mode. In contrast, higher-end PC systems of this era can operate 1024 × 768 at 72 Hz with a full 256-color display. AGA's highest resolution is 1440 × 580 (262 144 colors) in interlaced 50 Hz PAL mode, when overscan is used.

These missed opportunities in the AGA upgrade contributed to the Amiga ultimately losing technical leadership in the area of multimedia. After the long-delayed AAA was finally suspended, AGA was to be succeeded by the Hombre chipset, but this was ultimately cancelled due to Commodore's bankruptcy.

AGA is present in the CD32, Amiga 1200 and Amiga 4000.

Color depth

Color depth or colour depth (see spelling differences), also known as bit depth, is either the number of bits used to indicate the color of a single pixel, in a bitmapped image or video framebuffer, or the number of bits used for each color component of a single pixel. For consumer video standards, such as High Efficiency Video Coding (H.265), the bit depth specifies the number of bits used for each color component. When referring to a pixel, the concept can be defined as bits per pixel (bpp), which specifies the number of bits used. When referring to a color component, the concept can be defined as bits per component, bits per channel, bits per color (all three abbreviated bpc), and also bits per pixel component, bits per color channel or bits per sample (bps). Color depth is only one aspect of color representation, expressing the precision with which colors can be expressed; the other aspect is how broad a range of colors can be expressed (the gamut). The definition of both color precision and gamut is accomplished with a color encoding specification which assigns a digital code value to a location in a color space.

DEC Radix-50

RADIX-50, commonly called Rad-50, RAD50 or DEC Squoze, is an uppercase only character encoding created by Digital Equipment Corporation for use on their DECsystem, PDP, and VAX computers. RADIX-50's 40-character repertoire (050 in octal) can encode six characters plus four additional bits into one 36-bit word (PDP-6, PDP-10/DECsystem-10, DECSYSTEM-20); three characters plus two additional bits into one 18-bit word (PDP-9, PDP-15); or three characters into one 16-bit word (PDP-11, VAX).

The actual encoding differed between the 36-bit and 16-bit systems.


DECtape (originally called Microtape) is a magnetic tape data storage medium used with many Digital Equipment Corporation computers, including the PDP-6, PDP-8, LINC-8, PDP-9, PDP-10, PDP-11, PDP-12, and the PDP-15. On DEC's 32-bit systems, VAX/VMS support for it was implemented but did not become an official part of the product lineup.

DECtapes are 3/4 inch (19 mm) wide, and formatted into blocks of data that can each be read or written individually. Each tape stores 184K 12-bit PDP-8 words or 144K 18-bit words. Block size is 128 12-bit words (for the 12-bit machines), or 256 18-bit words for the other machines (16, 18, 32, or 36 bit systems). From a programming point of view, DECtape behaves like a very slow disk drive.

IBM 701

The IBM 701 Electronic Data Processing Machine, known as the Defense Calculator while in development, was IBM’s first commercial scientific computer, which was announced to the public on April 29, 1952. It was designed by Nathaniel Rochester and based on the IAS machine at Princeton. Its successor was the IBM 704, its computer siblings were the IBM 702 for business, and the lower-cost general-purpose IBM 650.


The LatticeMico8 is an 8-bit microcontroller soft processor core optimized for field-programmable gate arrays (FPGAs) and crossover programmable logic device architecture from Lattice Semiconductor. Combining a full 18-bit wide instruction set with 32 general purpose registers, the LatticeMico8 is a flexible Verilog reference design suitable for a wide variety of markets, including communications, consumer, computer, medical, industrial, and automotive. The core consumes minimal device resources, less than 200 look up tables (LUTs) in the smallest configuration, while maintaining a broad feature set.

The LatticeMico8 is licensed under a new free (IP) core license, the first such license offered by any FPGA supplier. The main benefits of using the IP core are greater flexibility, improved portability, and no cost. This new agreement provides some of the benefits of standard open source and allows users to mix proprietary designs with the core. Additionally, it allows for the distribution of designs in bitstream or FPGA format without accompanying it with a copy of the license. Developers are required to keep the core's source code confidential and use "for the sole purposes of design documentation and preparation of Derivative Works ... to develop designs to program Lattice programmable logic devices".

List of Nokia products

The following is a list of products branded by Nokia.


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 famous for being the computer most important in the creation of hacker culture at MIT, BBN and elsewhere. The PDP-1 is the original hardware for playing history's first game on a minicomputer, Steve Russell's Spacewar!


The PDP-15 was the fifth and last of the 18-bit minicomputers produced by Digital Equipment Corporation. The PDP-1 was first delivered in December 1959 and the first PDP-15 was delivered in February 1970. More than 400 of these successors to the PDP-9 (and 9/L) were ordered within the first eight months.


The PDP-4 was the successor to the Digital Equipment Corporation's PDP-1.


The PDP-7 was a minicomputer produced by Digital Equipment Corporation as part of the PDP series. Introduced in 1964, shipped since 1965, it was the first to use their Flip-Chip technology. With a cost of US$72,000, it was cheap but powerful by the standards of the time. The PDP-7 is the third of Digital's 18-bit machines, with essentially the same instruction set architecture as the PDP-4 and the PDP-9.


The PDP-9, the 4th 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.

Programmed Data Processor

Programmed Data Processor (PDP), referred to by some customers, media and authors as "Programmable Data Processor, is a term used by the Digital Equipment Corporation from 1957 to 1990 for several lines of minicomputers. The name "PDP" intentionally avoids the use of the term "computer" because, at the time of the first PDPs, computers had a reputation of being large, complicated, and expensive machines, and the venture capitalists behind Digital (especially Georges Doriot) would not support Digital's attempting to build a "computer"; the word "minicomputer" had not yet been coined. So instead, Digital used their existing line of logic modules to build a Programmed Data Processor and aimed it at a market that could not afford the larger computers.

The various PDP machines can generally be grouped into families based on word length.

Roland Sound Canvas

Roland/Edirol Sound Canvas lineup is a series of General MIDI based PCM sound modules and PC sound cards primarily intended for computer music usage, created by Japanese manufacturer Roland Corporation. Some models include serial or USB connection to computer.

The Sound Canvas engine has been widely used as a basis for most of Roland's electronic keyboard products, particularly the Interactive Arranger and Backing Keyboard lineups.

Sony Ericsson P910

The Sony Ericsson P910 is a smartphone by Sony Ericsson introduced in 3Q, 2004 and the successor of the Sony Ericsson P900. The P910 has a full QWERTY keyboard on the back of the flip (the flip can also be removed completely, allowing for a 'traditional' PDA form-factor). The biggest change from the P900 to the P910 is that the P910 supports Memory Stick PRO Duo and the phone's internal memory has been upped from 16 MB to 64 MB. Although Memory Stick PRO Duo comes in larger capacities, the maximum supported by the P910i is 2 GB. It is powered by an ARM9 processor clocked at 156 MHz and runs the Symbian OS with the UIQ graphical user interface. Also, the touchscreen displays 262,144 colours (an 18-bit colour depth), as opposed to the P900's 65,536 (16-bit). It comes in three versions:

P910i (GSM 900/1800/1900)

P910c (GSM 900/1800/1900 for China mainland)

P910a (GSM 850/1800/1900 for North America and Latin America)One of the key aspects of the P910 is its ability to input text via several methods: multi-tap and T9 text input using the numerical keypad, hand-writing recognition with the pre-installed Jot-Pro software and touchscreen, virtual keyboard on screen and the new QWERTY keyboard on the inside of the flip.

Other enhancements (compared to the P900) include support for HTML browsing, a new numerical keypad with larger keys and a slightly changed outer casing.

Its closest competitors are the palmOne Treo 650, and the Nokia 9500 Communicator. Other competitors include several PDA-phones powered by Windows and manufactured by Taiwan-based HTC.

Sony Ericsson released the successor to the P910 in early 2006. It is called the Sony Ericsson P990.


The TOPS-20 operating system by Digital Equipment Corporation (DEC) was a proprietary OS used on some of DEC's 36-bit

mainframe computers. The Hardware Reference Manual was described as for "DECsystem-10/DECSYSTEM-20 Processor" (meaning

the DEC PDP-10 and the DECSYSTEM-20).TOPS-20 began in 1969 as the TENEX operating system of Bolt, Beranek and Newman (BBN) and shipped as a product by DEC starting in 1976. TOPS-20 is almost entirely unrelated to the similarly named TOPS-10, but it was shipped with the PA1050 TOPS-10 Monitor Calls emulation facility which allowed most, but not all, TOPS-10 executables to run unchanged. As a matter of policy, DEC did not update PA1050 to support later TOPS-10 additions except where required by DEC software.

TOPS-20 competed with TOPS-10, ITS and WAITS—all available for the PDP-10

(all of which were notable time-sharing systems) during this timeframe.


The TX-0, for Transistorized Experimental computer zero, but affectionately referred to as tixo (pronounced "tix oh"), was an early fully transistorized computer and contained a then-huge 64K of 18-bit words of magnetic core memory. Construction of the TX-0 began in 1955 and ended in 1956. It was used continually through the 1960s at MIT. The TX-0 incorporated around 3600 Philco high-frequency surface-barrier transistors, the first transistor suitable for high-speed computers. The TX-0 and its direct descendant, the original PDP-1, were platforms for pioneering computer research and the development of what would later be called computer "hacker" culture.


The UNIVAC 418 was a transistorized, 18-bit word core memory machine made by Sperry Univac. The name came from its 4-microsecond memory cycle time and 18-bit word. The assembly language for this class of computers was TRIM III and ART418.

Over the three different models, more than 392 systems were manufactured. It evolved from the Control Unit Tester (CUT), a device used in the factory to test peripherals for larger systems.

Instruction set
Word size
Core count

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