PDP-1 at the Computer History Museum with Steve Russell, creator of Spacewar! The large cabinet houses the processor. The main control panel is just above the desk, the paper tape reader is above it (metallic), and the output of the Teletype model BRPE paper tape punch above that (vertical slot). A storage tray for eight fanfold paper tapes is attached to the top panel. At the left is the IBM Model Btypewriter modified by Soroban, and the Type 30 CRT display is to the far right.
The PDP-1 uses an 18-bitword size and has 4096 words as standard main memory (equivalent in bit size to 9,216 eight-bit bytes, but in character size to 12,388 bytes since the system actually divides an 18-bit word into three six-bit characters), upgradable to 65,536 words. The magnetic-core memory's cycle time is 5.35 microseconds (corresponding roughly to a clock speed of 187 kilohertz); 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 PDP-1 has computing power roughly equivalent to a 1996 pocket organizer and a little less memory.[4]
A System Building Block, seen end-onSystem Building Blocks 1103 hex-inverter cardPDP-1 System Building Block #4106, circa 1963, with a US quarter – note that one transistor (yellow) has been replaced
The PDP-1 uses 2,700 transistors and 3,000 diodes.[5] 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 5MHz. The System Building Blocks are packaged into several 19-inch racks. 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 solution, a punched tape reader and writer.
The design of the PDP-1 is based on the pioneering TX-0 and TX-2 computers, designed and built at MIT Lincoln Laboratory. Benjamin Gurley was the lead engineer on the project.[7] After showing a prototype at the Eastern Joint Computer Conference in December 1959, DEC delivered the first PDP-1 to Bolt, Beranek and Newman (BBN) in November 1960,[8][9] and it was formally accepted in early 1961.[10] In September 1961, DEC donated the PDP-1 to MIT,[11] where it was placed in the room next to its ancestor, the TX-0 computer,[12] 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, and served as the platform for a long list of computing innovations. This list includes one of the earliest digital video games, Spacewar!,[3] the first text editor, the first word processor, the first interactive debugger, the first credible computer chess program, one of the very earliest time-sharing systems (BBN Time-Sharing System), and some of the earliest computerized music.[13] At the Computer History Museum TX-0 alumni reunion in 1984, Gordon Bell said DEC's products developed directly from the TX-2, the successor to the TX-0 which had been developed at what Bell thought was a bargain price at the time, about US$3 million. At the same meeting, Jack Dennis said Ben Gurley's design for the PDP-1 was influenced by his work on the TX-0 display. [14]
The PDP-1 sold in basic form for US$120,000 (equivalent to US$1,223,519 in 2023).[15] BBN's system was quickly followed by orders from Lawrence Livermore and Atomic Energy of Canada (AECL), and eventually 53 PDP-1s were delivered until production ended in 1969.[16][17] 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, and from there ended up at the Computer History Museum (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 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.[18] AECL's computer was sent to Science North, 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.[19]
PDP-1 Type 30 point-mode CRT display and console typewriter, with processor frame in background
The PDP-1 uses fanfold punched paper tape as its primary storage medium.[15] Unlike punched card decks, which could be sorted and re-ordered, paper tape is tedious to physically edit. This inspired the creation of text-editing programs such as Expensive Typewriter and TECO. Because it is equipped with online and offline printers that were based on IBM electric typewriter mechanisms, it is capable of what, in 1980s terminology, would be called "letter-quality printing" and therefore inspired TJ-2, arguably the first word processor.
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 solenoids to activate the typebars. It uses a traditional typebar mechanism, not the "golfball" 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 Flexowriters 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.[23] 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 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. 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 disks 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 is a point plotting display device capable of addressing 1024 by 1024 addressable locations at a rate of 20,000 points per second.[24] A special "Display One Point On CRT" instruction is used to build up images, which have to be refreshed many times per second.[24] The CRT, which was originally developed for use in radar, is 16 inches (41cm) in diameter and uses a long-persistence P7 phosphor.[25] A light pen 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.[24]
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 filters). Music was prepared via Peter Samson's Harmony Compiler, a sophisticated text-based program with some features specifically oriented toward the efficient coding of baroque music. Several hours of music were prepared for it, including Bach fugues, all of Mozart's Eine kleine Nachtmusik, the Ode to Joy movement concluding Beethoven's Symphony No. 9, Christmas carols, and numerous popular songs.
Current status
PDP-1 Control Panel
Only three PDP-1 computers are still known to exist, and all three are in the collection of the Computer History Museum (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:
Software simulations of the PDP-1 exist in SIMH and MESS, hardware recreation through FPGA exists for the MiSTer project as well, and binary image of paper tapes of the software exist in the bitsavers.org archives.[26]
↑ Weik, Martin H. (March 1961). "Programmed Data Processor". Ed Thelen's Nike Missile Web Site. A Third Survey of Domestic Electronic Digital Computing Systems. Archived from the original on March 21, 2022. Retrieved July 6, 2018.
↑ Lichstein, Henry (November 20, 1963). "Telephone Hackers Active"(PDF). The Tech. Vol.83, no.24. p.1. Archived(PDF) from the original on February 16, 2022. Retrieved March 23, 2022.
↑ Mast, Bob (November 24, 1998). "From: Bob Mast". Blinkenlights Archæological Institute. Archived from the original on January 2, 2022. Retrieved March 22, 2022. The Flexowriter was first manufactured by IBM, during WWII, to be used as an automatic letter writer. After the war several IBMers bought the rights and formed Commercial Controls, Inc. They manufactured same in the old IBM Selectric typewriter building in Rochester NY. In the late fifties, Friden bought Commercial Controls.
Digital Equipment Corporation, using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president until he was forced to resign in 1992, after the company had gone into precipitous decline.
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, especially as the TOPS-10 operating system became widely used.
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.
TECO, short for Text Editor & Corrector, is both a character-oriented text editor and a programming language, that was developed in 1962 for use on Digital Equipment Corporation computers, and has since become available on PCs and Unix. Dan Murphy developed TECO while a student at the Massachusetts Institute of Technology (MIT).
The PDP-7 is an 18-bit 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 TX-0, for Transistorized Experimental computer zero, but affectionately referred to as tixo, 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 3,600 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. For MIT, this was the first computer to provide a system console which allowed for direct interaction, as opposed to previous computers, which required the use of punched card as a primary interface for programmers debugging their programs. Members of MIT's Tech Model Railroad Club, "the very first hackers at MIT", reveled in the interactivity afforded by the console, and were recruited by Marvin Minsky to work on this and other systems used by Minsky's AI group.
TYPSET is an early document editor that was used with the 1964-released RUNOFF program, one of the earliest text formatting programs to see significant use.
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 data word, which was at that time a common word size for large machines like IBM mainframes. The system was constructed using the same germanium transistor-based System Module layout as DEC's earlier machines, like the PDP-1 and PDP-4.
Stephen Russell, also nicknamed "Slug", is an American computer scientist most famous for creating Spacewar!, well known for being the first widely distributed video game.
The Friden Flexowriter was a teleprinter produced by the Friden Calculating Machine Company. It was a heavy-duty electric typewriter capable of being driven not only by a human typing, but also automatically by several methods, including direct attachment to a computer and by use of paper tape.
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.
Alan Kotok was an American computer scientist known for his work at Digital Equipment Corporation and at the World Wide Web Consortium (W3C). Steven Levy, in his book Hackers: Heroes of the Computer Revolution, describes Kotok and his classmates at the Massachusetts Institute of Technology (MIT) as the first true hackers.
Spacewar! is a space combat video game developed in 1962 by Steve Russell in collaboration with Martin Graetz, Wayne Wiitanen, Bob Saunders, Steve Piner, and others. It was written for the newly installed DEC PDP-1 minicomputer at the Massachusetts Institute of Technology. After its initial creation, Spacewar! was expanded further by other students and employees of universities in the area, including Dan Edwards and Peter Samson. It was also spread to many of the few dozen installations of the PDP-1 computer, making Spacewar! the first known video game to be played at multiple computer installations.
Peter R. Samson is an American computer scientist, best known for creating pioneering computer software for the TX-0 and PDP-1.
Expensive Desk Calculator by Robert A. Wagner is thought to be computing's first interactive calculation program.
Expensive Tape Recorder is a digital audio program written by David Gross while a student at the Massachusetts Institute of Technology. Gross developed the idea with Alan Kotok, a fellow member of the Tech Model Railroad Club. The recorder and playback system ran in the late 1950s or early 1960s on MIT's TX-0 computer on loan from Lincoln Laboratory.
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.
Information Control Systems was a computer programming and data processing company serving clients in the Midwestern United States.
Mainframe computers are computers used primarily by businesses and academic institutions for large-scale processes. Before personal computers, first termed microcomputers, became widely available to the general public in the 1970s, the computing industry was composed of mainframe computers and the relatively smaller and cheaper minicomputer variant. During the mid to late 1960s, many early video games were programmed on these computers. Developed prior to the rise of the commercial video game industry in the early 1970s, these early mainframe games were generally written by students or employees at large corporations in a machine or assembly language that could only be understood by the specific machine or computer type they were developed on. While many of these games were lost as older computers were discontinued, some of them were ported to high-level computer languages like BASIC, had expanded versions later released for personal computers, or were recreated for bulletin board systems years later, thus influencing future games and developers.
Robert Alan Saunders is an American computer scientist, most famous for being an influential computer programmer. Saunders joined the Tech Model Railroad Club (TMRC) led by Alan Kotok, Peter Samson, and himself. They then met Marvin Minsky and other influential pioneers in what was then known as Artificial Intelligence.
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