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The PDP-1 (''Programmed Data Processor-1'') is the first
computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as Computer program, programs. These ...

computer
in
Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark A trademark (also written trade mark or trade-mark) is a type of intellectual property Intellectual property (IP) is a category of property Property is a system of rights ...
's PDP series and was first produced in 1959. It is famous for being the computer most important in the creation of
hacker culture The hacker culture is a subculture A subculture is a group of people within a culture Culture () is an umbrella term which encompasses the social behavior and Norm (social), norms found in human Society, societies, as well as the knowle ...

hacker culture
at
Massachusetts Institute of Technology Massachusetts Institute of Technology (MIT) is a private Private or privates may refer to: Music * "In Private "In Private" was the third single in a row to be a charting success for United Kingdom, British singer Dusty Springfield, aft ...
, BBN and elsewhere. The PDP-1 is the original hardware for playing history's first game on a
minicomputer A minicomputer, or colloquially mini, is a class of smaller general purpose computers that developed in the mid-1960s and sold for much less than Mainframe computer, mainframe and mid-size computers from IBM and BUNCH, its direct competitors. In ...
, Steve Russell's ''
Spacewar! ''Spacewar!'' is a space combat Space warfare will be combat that will take place in outer space Outer space is the expanse that exists beyond Earth and between astronomical object, celestial bodies. Outer space is not completely empty ...
''


Description

The PDP-1 uses an
18-bit 18 binary digits have (1000000 octal The octal numeral system, or oct for short, is the radix, base-8 number system, and uses the Numerical digit, digits 0 to 7, that is to say 10 represents 8 in decimal and 100 represents 64 in decimal. How ...
word In linguistics Linguistics is the scientific study of language A language is a structured system of communication used by humans, including speech (spoken language), gestures (Signed language, sign language) and writing. Most lang ...
size and has 4096 words as standard
main memory Computer data storage is a technology consisting of computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations automatically. Modern computers can perform ...
(equivalent to 9,216 eight-bit
byte The byte is a unit of digital information that most commonly consists of eight bit The bit is a basic unit of information in computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It ...
s, though the system actually divides an 18-bit word into six-bit characters), upgradable to 65,536 words. The
magnetic-core memory Magnetic-core memory was the predominant form of random-access Random access (more precisely and more generally called direct access) is the ability to access an arbitrary element of a sequence in equal time or any datum from a population of ...
's cycle time is 5.35
microsecond A microsecond is an SI unit of time equal to one millionth (0.000001 or 10−6 or ) of a second The second (symbol: s, abbreviation: sec) is the SI base unit, base unit of time in the International System of Units (SI) (French: Système In ...
s (corresponding roughly to a "
clock speed In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and softwar ...
" of 187
kilohertz The hertz (symbol: Hz) is the unit Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action ...
); consequently most arithmetic instructions take 10.7 microseconds (93,458 operations per second) because they use two memory cycles: the first to fetch the instruction, the second to fetch or store the data word. Signed numbers are represented in
ones' complement The ones' complement of a binary number In mathematics and digital electronics Digital electronics is a field of electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behavi ...
. The PDP-1 has computing power roughly equivalent to a 1996 pocket organizer and a little less memory. The PDP-1 uses 2,700
transistors file:MOSFET Structure.png, upright=1.4, Metal-oxide-semiconductor field-effect transistor (MOSFET), showing Metal gate, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A ...
and 3,000 diodes. It is built mostly of DEC 1000-series System Building Blocks, using micro-alloy and micro-alloy diffused transistors with a rated switching speed of 5 MHz. The System Building Blocks are packaged into several
19-inch rack A 19-inch rack is a standardized frame or enclosure for mounting multiple electronic equipment modules. Each module has a front panel that is wide. The 19 inch dimension includes the edges or "ears" that protrude from each side of the equi ...
s. The racks are themselves packaged into a single large mainframe case, with a hexagonal control panel containing switches and lights mounted to lie at table-top height at one end of the mainframe. Above the control panel is the system's standard
input/output In computing, input/output (I/O, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, possibly a human or another information processing system. Information, Inputs are ...
solution, a
punched tape Five- and eight-hole punched paper tape Paper tape reader on the Harwell computer with a small piece of five-hole tape connected in a circle – creating a physical program loop Punched tape or perforated paper tape is a form of data storage ...

punched tape
reader and writer. The PDP-1 weighed about .


History

The design of the PDP-1 is based on the pioneering
TX-0 The TX-0, for ''Transistorized Experimental computer zero'', but affectionately referred to as tixo (pronounced "tix oh"), was an early fully transistor upright=1.4, gate Candi bentar, a typical Indonesian gate that is often found on ...
and
TX-2 The MIT Massachusetts Institute of Technology (MIT) is a private land-grant research university A research university is a university A university ( la, universitas, 'a whole') is an educational institution, institution of higher e ...
computers, designed and built at
MIT Lincoln Laboratory The MIT Lincoln Laboratory, located in Lexington, Massachusetts Lexington is a suburban town in Middlesex County, Massachusetts, United States. It is 10 miles (16 km) from Downtown Boston. The population was 34,454 as of the 2020 census. ...
. Benjamin Gurley was the lead engineer on the project. After showing a prototype at the
Eastern Joint Computer Conference The Joint Computer Conferences were a series of computer conferences in the USA held under various names between 1951 and 1987. The conferences were the venue for presentations and papers representing "cumulative work in the omputerfield." Ori ...
in December 1959, DEC delivered the first PDP-1 to
Bolt, Beranek and Newman Raytheon BBN Technologies (originally Bolt Beranek and Newman Inc.) was an American research and development company, based next to Fresh Pond in Cambridge, Massachusetts Cambridge ( ) is a city in Middlesex County, Massachusetts, Middlesex C ...
(BBN) in November 1960, and it was formally accepted in early 1961. In September 1961, DEC donated the PDP-1 to MIT, where it was placed in the room next to its ancestor, the TX-0 computer, which was by then on indefinite loan from Lincoln Laboratory. In this setting, the PDP-1 quickly replaced the TX-0 as the favorite machine among the budding
hacker culture The hacker culture is a subculture A subculture is a group of people within a culture Culture () is an umbrella term which encompasses the social behavior and Norm (social), norms found in human Society, societies, as well as the knowle ...

hacker culture
, and served as the platform for a long list of computing innovations. This list includes one of the earliest digital video games, ''
Spacewar! ''Spacewar!'' is a space combat Space warfare will be combat that will take place in outer space Outer space is the expanse that exists beyond Earth and between astronomical object, celestial bodies. Outer space is not completely empty ...
'', the first
text editor A text editor is a type of computer program In imperative programming, a computer program is a sequence of instructions in a programming language that a computer can execute or interpret. In declarative programming, a ''computer program'' is ...

text editor
, the first
word processor A word processor (WP) is a device or computer program that provides for input, editing, formatting, and output of text, often with some additional features. Early word processors were stand-alone devices dedicated to the function, but current ...
, the first interactive
debugger A debugger or debugging tool is a computer program In imperative programming, a computer program is a sequence of instructions in a programming language that a computer can execute or interpret. In declarative programming, a ''computer progra ...

debugger
, the first credible
computer chess Computer chess includes both hardware (dedicated computers) and Computer software, software capable of playing chess. Computer chess provides opportunities for players to practice even in the absence of human opponents, and also provides opport ...
program, one of the very earliest time-sharing systems (
BBN Time-Sharing System The BBN Time-Sharing System was an early Time-sharing, time-sharing system created at BBN Technologies, Bolt, Beranek and Newman (BBN) for the PDP-1 computer. It began operation in September 1962. Digital Equipment Corporation's prototype PDP-1 wa ...
), and some of the earliest computerized music. At the Computer History Museum
TX-0 The TX-0, for ''Transistorized Experimental computer zero'', but affectionately referred to as tixo (pronounced "tix oh"), was an early fully transistor upright=1.4, gate Candi bentar, a typical Indonesian gate that is often found on ...
alumni reunion in 1984,
Gordon Bell Chester Gordon Bell (born August 19, 1934) is an American electrical engineer Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, el ...

Gordon Bell
said DEC's products developed directly from the
TX-2 The MIT Massachusetts Institute of Technology (MIT) is a private land-grant research university A research university is a university A university ( la, universitas, 'a whole') is an educational institution, institution of higher e ...
, the successor to the TX-0 which had been developed at what Bell thought was a bargain price at the time, about . At the same meeting,
Jack Dennis Jack Bonnell Dennis (born October 13, 1931) is a computer scientist A computer scientist is a person who has acquired the knowledge of computer science Computer science deals with the theoretical foundations of information, algorithms a ...

Jack Dennis
said Ben Gurley's design for the PDP-1 was influenced by his work on the TX-0 display. The PDP-1 sold in basic form for . BBN's system was quickly followed by orders from Lawrence Livermore and
Atomic Energy of Canada Atomic Energy of Canada Limited (AECL; french: Énergie atomique du Canada limitée (''EACL'')) is a Canadian Canadians (french: Canadiens) are people identified with the country of Canada Canada is a country in the northern part ...
(AECL), and eventually 53 PDP-1s were delivered until production ended in 1969. All of these machines were still being actively used in 1970, and several were eventually saved. MIT's example was donated to
The Computer Museum, Boston The Computer Museum was a Boston Boston (, ), officially the City of Boston, is the capital city, capital and List of municipalities in Massachusetts, most populous city of the Commonwealth (U.S. state), Commonwealth of Massachusetts in the U ...
, and from there ended up at the
Computer History Museum The Computer History Museum (CHM) is a museum of computer history, located in Mountain View, California. The museum presents stories and artifacts of Silicon Valley and the information age, and explores the computing revolution and its impact on s ...
(CHM). A late version of ''Spacewar!'' on paper tape was still tucked into the case. PDP-1 #44 was found in a barn in
Wichita, Kansas Wichita ( ) is the largest city in the U.S. state In the United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country Contiguous United States, primarily located in N ...
in 1988, apparently formerly owned by one of the many aviation companies in the area, and rescued for the Digital Historical Collection, also eventually ending up at the CHM. AECL's computer was sent to
Science North Science North (french: Science Nord) is an interactive science museum in Greater Sudbury, Ontario, Canada. The science centre, which is Northern Ontario's most popular tourist attraction, consists of two snowflake-shaped buildings on the southwes ...
, but was later scrapped. The launch of the PDP-1 marked a radical shift in the philosophy of computer design: it is the first commercial computer that focuses on interaction with the user rather than just the efficient use of computer cycles. The first ever reference to malicious hacking is ' telephone hackers' in
MIT Massachusetts Institute of Technology (MIT) is a private land-grant research university A research university is a university A university ( la, universitas, 'a whole') is an educational institution, institution of higher education, hi ...
's student newspaper, '' The Tech'' of hackers tying up the lines with
Harvard Harvard University is a private Private or privates may refer to: Music * "In Private "In Private" was the third single in a row to be a charting success for United Kingdom, British singer Dusty Springfield, after an absence of nearly t ...

Harvard
, configuring the PDP-1 to make free calls,
war dialing Wardialing (or war dialing) is a technique to automatically scan a list of telephone numbers, usually dialing every number in a area code, local area code to search for modems, computers, bulletin board systems (computer servers) and fax machines. ...
and accumulating large phone bills.


Peripherals

The PDP-1 uses punched
paper tape Five- and eight-hole punched paper tape Paper tape reader on the Harwell computer with a small piece of five-hole tape connected in a circle – creating a physical program loop Punched tape or perforated paper tape is a form of data storage ...

paper tape
as its primary storage medium. Unlike
punched card A punched card (also punch cardSteven Pinker, in ''The Stuff of Thought'', Viking, 2007, p.362, notes the loss of ''-ed'' in pronunciation ''as it did in ice cream, mincemeat, and box set, formerly iced cream, minced meat, and boxed set.'' or p ...

punched card
decks, which could be sorted and re-ordered, paper tape is difficult to physically edit. This inspired the creation of text-editing programs such as
Expensive Typewriter Expensive Typewriter was a text editing program that ran on the DEC PDP-1 The PDP-1 (''Programmed Data Processor-1'') is the first computer in Digital Equipment Corporation's Programmed Data Processor, PDP series and was first produced in 1959 ...
and TECO. Because it is equipped with online and offline printers that were based on
IBM International Business Machines Corporation (IBM) is an American multinational technology company headquartered in Armonk, New York, with operations in over 170 countries. The company began in 1911, founded in Endicott, New York, as the C ...

IBM
electric
typewriter A typewriter is a mechanical Mechanical may refer to: Machine * Mechanical system A machine is any physical system with ordered structural and functional properties. It may represent human-made or naturally occurring device molecular ...

typewriter
mechanisms, it is capable of what, in 1980s terminology, would be called " letter-quality printing" and therefore inspired
TJ-2 TJ-2 (Type Justifying Program) was published by Peter Samson in May 1963 and is thought to be the first page layout program. Although it lacks page numbering, page headers and Page footer, footers, TJ-2 is the first word processor to provide a numb ...
, arguably the first
word processor A word processor (WP) is a device or computer program that provides for input, editing, formatting, and output of text, often with some additional features. Early word processors were stand-alone devices dedicated to the function, but current ...
. The console typewriter is the product of a company named Soroban Engineering. It uses an IBM Model B Electric typewriter mechanism, modified by the addition of switches to detect keypresses, and
solenoid A solenoid (,) is a type of electromagnet File:VFPt Solenoid correct2.svg, Magnetic field produced by a solenoid (coil of wire). This drawing shows a cross section through the center of the coil. The crosses are wires in which current is ...

solenoid
s to activate the . It uses a traditional typebar mechanism, not the "golfball"
IBM Selectric typewriter The IBM Selectric typewriter was a highly successful line of electric typewriter File:Typewriter.ogv, Video showing the operation of a typewriter A typewriter is a machine, mechanical or electromechanical machine for typing characters. T ...

IBM Selectric typewriter
mechanism, which was not introduced until the next year. Lettercase is selected by raising and lowering the massive type basket. The Soroban is equipped with a two-color inked ribbon (red and black), and the interface allows color selection. Programs commonly use color-coding to distinguish user input from machine responses. The Soroban mechanism is unreliable and prone to jamming, particularly when shifting case or changing ribbon color. Offline devices are typically
Friden Flexowriter The Friden Flexowriter was a teleprinter A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point ( ...
s that have been specially built to operate with the FIO-DEC character coding used by the PDP-1. Like the console typewriter, these are built around a typing mechanism that is mechanically the same as an
IBM Electric typewriter The IBM Electric typewriters were a series of electric typewriters that IBM manufactured, starting in the mid-1930s. They used the conventional moving carriage and typebar mechanism, as opposed to the fixed carriage and type ball used in the IBM ...
. However, Flexowriters are highly reliable and were often used for long unattended printing sessions. Flexowriters have electromechanical paper tape punches and readers which operate synchronously with the typewriter mechanism. Typing rates are about ten characters per second. A typical PDP-1 operating procedure is to output text to punched paper tape using the PDP-1's "high speed" (60-character-per-second) Teletype model BRPE punch, then to hand carry the tape to a Flexowriter for offline printing. In later years,
DECtape 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, OpenVM ...

DECtape
drives were added to some PDP-1 systems, as a more convenient method of backing up programs and data, and to enable early
time-sharing In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and sof ...
. This latter application usually requires a secondary storage medium for swapping programs and data in and out of core memory, without requiring manual intervention. For this purpose, DECtapes are far superior to paper tapes, in terms of reliability, durability, and speed. Early
hard disk A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device On a reel-to-reel tape recorder (Sony TC-630), the recorder is data storage equipment and the magnetic tape is a data stora ...

hard disk
s were expensive and notoriously unreliable; if available and working, they are used primarily for speed of swapping, and not for permanent file storage.


Graphics display

The Type 30 Precision
CRT display A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, the beams of which are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms (oscilloscope), pictures (televisi ...
is a point plotting display device capable of addressing 1024 by 1024 addressable locations at a rate of 20,000 points per second. A special "Display One Point On CRT" instruction is used to build up images, which have to be refreshed many times per second. The CRT, which was originally developed for use in radar, is in diameter and uses a long-persistence P7 phosphor. A
light pen A light pen is a computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as Com ...
can be used with the Type 30 to pick points on the display. An optional character generator and hardware for line and curve generation are available.


Computer music

MIT hackers also used the PDP-1 for playing music in four-part harmony, using some special hardware – four flip-flops directly controlled by the processor (the audio signal is filtered with simple
RC filter A resistor–capacitor circuit (RC circuit), or RC filter or RC network, is an electric circuit An electrical network is an interconnection of electrical components (e.g., batteries, resistors, inductor An inductor, also called a coil, c ...

RC filter
s). Music was prepared via
Peter Samson Peter R. Samson (born 1941 in Fitchburg, Massachusetts Fitchburg is a city in northern Worcester County, Massachusetts, Worcester County, Massachusetts, United States. The third-largest city in the county, its population was 41,946 at the 2020 U ...
's ''
Harmony Compiler Harmony Compiler was written by Peter Samson at the Massachusetts Institute of Technology (MIT). The compiler was designed to encode music for the PDP-1 and built on an earlier program Samson wrote for the TX-0 computer. ] Jack Dennis noticed and ...
'', a sophisticated text-based program with some features specifically oriented toward the efficient coding of
baroque music Baroque music ( or ) is a period or style of Western classical music Classical music is art music produced or rooted in the traditions of Western culture, including both Religious music, liturgical (Religion, religious) and secular music, sec ...
. Several hours of music were prepared for it, including Bach
fugue In music Music is the of arranging s in time through the of melody, harmony, rhythm, and timbre. It is one of the aspects of all human societies. General include common elements such as (which governs and ), (and its associated con ...
s, all of Mozart's '' Eine kleine Nachtmusik'', the ''
Ode to Joy "Ode to Joy" (German language, German: , literally "To Joy") is an ode written in the summer of 1785 in literature, 1785 by German poet, playwright, and historian Friedrich Schiller and published the following year in ''Thalia (magazine), ...
'' movement concluding Beethoven's ''Symphony No. 9'', Christmas carols, and numerous popular songs.


Current status

Only three PDP-1 computers are still known to exist, and all three are in the collection of the
Computer History Museum The Computer History Museum (CHM) is a museum of computer history, located in Mountain View, California. The museum presents stories and artifacts of Silicon Valley and the information age, and explores the computing revolution and its impact on s ...
(CHM). One is the prototype formerly used at MIT, and the other two are production PDP-1C machines. One of the latter, serial number 55 (the last PDP-1 made) has been restored to working order, is on exhibit, and is demonstrated on two Saturdays every month. The demonstrations include: * the game ''
Spacewar! ''Spacewar!'' is a space combat Space warfare will be combat that will take place in outer space Outer space is the expanse that exists beyond Earth and between astronomical object, celestial bodies. Outer space is not completely empty ...
'' * graphics demonstrations such as Snowflake * playing music Software simulations of the PDP-1 exist in
SIMH SIMH is a highly portable, multi-system emulator which runs on Microsoft Windows, Windows, Linux, macOS, FreeBSD, OpenBSD, NetBSD and OpenVMS. It is maintained by Bob Supnik, a former Digital Equipment Corporation, DEC engineer and DEC vice presi ...
and
MESS The mess (also called a mess deck aboard ships) is an area where military personnel Military personnel are members of the state's armed forces A military, also known collectively as armed forces, is a heavily armed, highly organized forc ...

MESS
, and
binary image A binary image is one that consists of pixels that can have one of exactly two colors, usually black and white. Binary images are also called ''bi-level'' or ''two-level''. This means that each pixel is stored as a single bit—i.e., a 0 or 1. ...
paper tapes of the software exist in the bitsavers.org archives.
/ref>


See also

*
History of computers The history of computing hardware covers the developments from early simple devices to aid calculation to modern day computers. Before the 20th century, most calculations were done by humans. Early mechanical tools to help humans with digital ...
*
History of computer science The history of computer science began long before our modern discipline of computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical te ...
*''
Spacewar! ''Spacewar!'' is a space combat Space warfare will be combat that will take place in outer space Outer space is the expanse that exists beyond Earth and between astronomical object, celestial bodies. Outer space is not completely empty ...
'' *
Tech Model Railroad Club The Tech Model Railroad Club (TMRC) is a student organization at the Massachusetts Institute of Technology (MIT). Historically it has been a wellspring of hacker culture and the oldest such hacking group in North America. Formed in 1946, its HO sc ...
*
Timeline of computing Timeline of computing presents events in the history of computing organized by year and grouped into six topic areas: predictions and concepts, first use and inventions, hardware systems and processors, operating systems, programming languages, an ...


Notes


External links


Restoring the DEC PDP-1 Computer Exhibit
— The
Computer History Museum The Computer History Museum (CHM) is a museum of computer history, located in Mountain View, California. The museum presents stories and artifacts of Silicon Valley and the information age, and explores the computing revolution and its impact on s ...
's restoration project
DEC PDP-1 Collection
at the Computer History Museum – includes Moving Image resources on their PDP-1 and the restoration project, and some music files in the Audio section.
DEC PDP-1 information
– DEC's 1963 ''Programmed Data Processor-1 Handbook''
bitsavers.org PDP-1 directory
– Scanned documentation incl PDP-1 handbook, maintenance manual, price list, diagnostic documentation, etc.
PDP-1 Music
– Listen to MP3s of music created on the PDP-1
The Dot Eaters entry
on the PDP-1 and its use in the development of the first videogame, Spacewar!

from the original DEC documentation, including letters of delivery, price sheets, and photos.
PDP-1 emulator in JavaScript running Spacewar! code.DEC PDP-1 music (video on YouTube)FPGA re-creation of PDP-1 with CRT, console and teletypeHistory of the PDP-1 at Stanford UniversityPhoto of PDP-1 at LRNL.
{{DEFAULTSORT:Pdp-1 DEC hardware Minicomputers Transistorized computers 18-bit computers Computer-related introductions in 1959 Computer-related introductions in 1960