DAC-1
Encyclopedia
DAC-1, for Design Augmented by Computer, was one of the earliest graphical computer aided design systems. Developed by General Motors
, IBM
was brought in as a partner in 1960 and the two developed the system and released it to production in 1963. It was publicly unveiled at the fall Joint Computer Conference in Detroit 1964. GM used the DAC system, continually modified, into the 1970s when it was succeeded by CADANCE.
machines as early as 1952 for engineering analysis. In 1955 they moved their computing services into the new Data Processing department of GM Research Laboratories. In 1956, together with North American Aviation
, they developed the first "official" batch processing
operating system
for IBM systems, GM-NAA I/O
. In 1958 they were one of the earliest users of IBM's new FORTRAN
compiler.
In June 1958 GM Research started a program to better understand the problems and potential improvements in the industrial design
process. The team found that each step of the process -from initial conception and body styling through engineering design and finally to detailed parts drawings- used different types of diagrams. Each division within the company had to have their own drawing departments to support them. Time was being lost, and errors introduced, when the diagrams moved from one department to another and had to be re-drawn into the local format. Even the task of looking up the diagrams in the engineering libraries represented a significant amount of time. When modifications were made to drawings, this process repeated itself.
Convinced that automation was a solution to at least some of these problems, in 1959 Donald Hart tasked the Data Processing department of GM Research to start developing a system to store diagrams for rapid retrieval and simple modifications. The idea was that the diagrams would be digitized into the computer, displayed interactively to allow rotations, scaling and projections, and then printed on demand. Lookups would be handled via punched card
queries, which would allow operators to quickly retrieve documents for manipulation into whatever local format the user needed, and then print it. Repetitive queries could be automated simply by saving the card stack.
computer displaying points on the IBM 780 display which were recorded to 8 mm film. One early use was plotting traffic simulations. However, the displays were not based on storage tube
s, so the images disappeared shortly after they were drawn. In order to keep the image on the screen, the program had to be put into a loop, continually refreshing the display. While this was happening the computer could not be used for other tasks. Although it was suitable for demonstration purposes, a real-world system would need additional hardware to offload this task from the CPU
.
Another problem was printing the diagrams. GM solved this problem by using an approach developed by Boeing
, replacing the milling head of a computerized milling machine with a ball-point pen and connecting the inputs of the mill to the 704 computer. To address the extremely limited amount of memory available on the 704, they broke the diagrams down into 32-by-32-inch squares, which could be plotted with enough accuracy that they could be loaded up as separate tiles and still line up perfectly when plotted as part of complete diagrams. A set of rollers were added to allow the plotter to move a single 96 inches (2,438.4 mm) piece of paper around the drawing surface on demand, meaning that the paper did not have to be cut into pieces. The paper was delivered in rolls, allowing diagrams to be any length.
The final problem was to convert the existing diagrams, on paper, into computer data. The solution was to re-print the diagrams onto clear acetate and place them in front of the 780 display. The computer then moved the display's dot across the screen, where it would be periodically occluded by the lines on the acetate. A photomultiplier
tube noticed these drops in output and recorded them. Since diagrams consist largely of whitespace and a few lines, a simple raster scan would be too time consuming. Instead, when the program noticed a line it would scan a circle of points around the last hit, attempting to find the line again. The system allowed the digitizing of 6,000 points a second. The output was a set of cubic polynomials that described the line smoothly.
computer and develop commercial versions of the display hardware.
The production system had to not only manipulate existing drawings, but also be capable of modifying them in the computer. Although the computer would not normally be used to produce new artwork, once the diagrams were scanned into the system, changes could be made without going through the entire scanning process again.
Once digitized, additional software could be used to convert the lines into a 3D shape. This was groundbreaking research at the time, and generated a flurry of research papers. Once converted, the diagrams could be output into the APT numerical control
language for direct output on milling machines. This would allow a design team to sketch out their ideas, put them into the system and clean them up, and then have the milling systems produce a physical model.
system, and a custom controller to drive multiple graphical terminals. Output from the terminals could be sent to a plotter, 35 mm slide film. IBM estimated the system would be installed within 18 months after signing the contract. GM accepted the offer in November 1960.
Development took longer than expected. While the 7090 was being installed at GM Research in Warren, MI, the GM teams were given use of one of IBM's own 7090s in Kingston, NY. As the original production date grew closer the number of GM employees traveling to NY became a serious budget problem, which was addressed when GM rented a Convair
aircraft for ferry flights between the two sites. A more serious problem was the scanner system, and a joint GM-IBM team was able to finally address the issues.
The system was given a full demonstration run at IBM's Kingston site in December 1962. The demonstrations were so well attended that bleacher
s were set up so that all of the attendees could see the terminal screen. The high usage demands during the demos eventually led to the disk system crashing. The production DAC-1 system went live in Warren in April 1963. At the time the 1301 was not ready, so a IBM 1401
and IBM 1405 were used instead.
DAC-1 was one of the earliest production CAD systems to enter use, only the Itek
built Digigraphics
system beat it, albeit to the extent of a single machine before it was taken over by Control Data Corporation
.
In November 1963, DAC-1 was used to create a model of a trunk lid in a straight-through manner. An original sketch was read in, cleaned up on the terminal, converted into 3D and then output to a milling machine
.
graphics terminal, 2280 film recorder and 2281 film scanner. Unlike the DAC-1's 7090, the Alpine products were all aimed for use with the newly announced IBM 360 series of computers. The graphics terminal was quite successful and IBM became a major CAD vendor. The film printer and scanner found little use among customers that were moving to all-digital workflows, and were later withdrawn as supported products.
When polled, team leaders within the project universally pointed to the batch-oriented operating system as the primary impediment to a truly interactive design system, with computer performance and a hierarchical file system as secondary concerns. This led to the MCTS system, "Multi-Console Time Sharing", a version of Multics
adapted for their own use, which they developed on the CDC STAR-100
computer.
, known, as was typical at the time, simply as "monitor". Monitor was based on the earlier batch processing systems developed at GM and IBM, but fed in the batches not from punched cards, but from the attached channel controllers instead. Terminals that had to exchange information with the host computer would place data in the controller for relay, which would cause an interrupt. The host machine would service the interrupt by copying the data from the terminal into the batch monitor, which would run it as if the input had come from a card stack. The DAC program consisted of a variety of small programs which were called by the batch monitor. Their output was then copied back to the terminals as if they were printers. Users who were not actively interacting with the terminals at any given time automatically gave up their time to other users. Although the term was not in widespread use at the time, the DAC-1 system was thus an early example of a time-sharing system.
Unlike traditional batch systems, where operators manually scheduled workflows for fastest possible access to resources, DAC-1's workload would be unpredictable. This led to potential situations where one request could take a device offline for servicing, changing tapes for instance, only to have the next request data from that device. Although no general solution to the problem was found, the programmers invested considerable effort in ensuring that all of the modules needed for a particular operation could be loaded in a single "clump".
The original 7090 had a single 32 kbyte bank of memory. In order to improve performance, the DAC-1 software was left in the core, isolated in one of two 16 kbyte logical banks. The other 16 kbytes held the batch monitor and an interrupt controller that drove it. With the introduction of the 7094, the two programs were separated into their own 32 kbyte physical stores. This left little room for user programs and data. After the DAC-1 was first installed, the original 7090 was relegated to other tasks and was replaced by an IBM 7094-II. In addition to being faster, this machine was equipped with two 32 kbyte core memory stores, an unusual arrangement. The two banks allowed DAC to have an entire 32 kbytes to itself.
derivative from the University of Michigan
, MAD (Michigan Algorithm Decoder), adding to it and creating their own version, NOMAD. NOMAD also included the ability to allow code to run anywhere in memory, which was very important, especially on the earlier machine with limited memory. Over 90% of the DAC system was written in NOMAD.
A similar language was also developed for the special task of running on the channel controllers. The new language was named "Maybe", because it was not clear whether or not it would work. Maybe turned into a joint effort between GM and the University of Michigan, and was indeed used on the production system.
The DAC-1 system also included a custom language intended for the users, not the programmers. DGL, for descriptive geometry language" was a simple domain-specific language that contained a number of basic geometrical operators and variable assignment. Users could write programs in DGL and input them into DAC using punched cards. The result were new modules that the user could call within the interactive environment.
The IBM design used a capacitance screen
with a metal pencil for input, providing a directly read X and Y coordinate. The basic system was similar to modern touch screen systems like the iPhone
, but not sensitive enough to detect a finger and instead required a wired conductor to complete the circuit. The pencil replaced the light pens because it was much faster to decode; a light pen had to wait for a pulse of light when a vector was being redrawn and then work its way through the list of vectors to find out which one was selected.
In use it was quickly discovered that holding the pen to the vertical monitor screen was extremely tiring, so the idea of using the terminal for input was abandoned. The GM team later visited Douglas Engelbart
's lab where they saw the first computer mouse, and based future projects on this device instead.
All of the terminals were connected to a single controller, and in turn to the 7090 via its Channel C input. Channel A and B were used to control magnetic tape
drives, and Channel D controlled the 1301 disk.
General Motors
General Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...
, IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
was brought in as a partner in 1960 and the two developed the system and released it to production in 1963. It was publicly unveiled at the fall Joint Computer Conference in Detroit 1964. GM used the DAC system, continually modified, into the 1970s when it was succeeded by CADANCE.
Genesis
GM was an early computer user, using punched cardPunched card
A punched card, punch card, IBM card, or Hollerith card is a piece of stiff paper that contains digital information represented by the presence or absence of holes in predefined positions...
machines as early as 1952 for engineering analysis. In 1955 they moved their computing services into the new Data Processing department of GM Research Laboratories. In 1956, together with North American Aviation
North American Aviation
North American Aviation was a major US aerospace manufacturer, responsible for a number of historic aircraft, including the T-6 Texan trainer, the P-51 Mustang fighter, the B-25 Mitchell bomber, the F-86 Sabre jet fighter, the X-15 rocket plane, and the XB-70, as well as Apollo Command and Service...
, they developed the first "official" batch processing
Batch processing
Batch processing is execution of a series of programs on a computer without manual intervention.Batch jobs are set up so they can be run to completion without manual intervention, so all input data is preselected through scripts or command-line parameters...
operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
for IBM systems, GM-NAA I/O
GM-NAA I/O
The GM-NAA I/O input/output system of General Motors and North American Aviation was the first operating system for the IBM 704 computer.It was created in 1956 by Robert L. Patrick of General Motors Research and Owen Mock of North American Aviation...
. In 1958 they were one of the earliest users of IBM's new FORTRAN
Fortran
Fortran is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing...
compiler.
In June 1958 GM Research started a program to better understand the problems and potential improvements in the industrial design
Industrial design
Industrial design is the use of a combination of applied art and applied science to improve the aesthetics, ergonomics, and usability of a product, but it may also be used to improve the product's marketability and production...
process. The team found that each step of the process -from initial conception and body styling through engineering design and finally to detailed parts drawings- used different types of diagrams. Each division within the company had to have their own drawing departments to support them. Time was being lost, and errors introduced, when the diagrams moved from one department to another and had to be re-drawn into the local format. Even the task of looking up the diagrams in the engineering libraries represented a significant amount of time. When modifications were made to drawings, this process repeated itself.
Convinced that automation was a solution to at least some of these problems, in 1959 Donald Hart tasked the Data Processing department of GM Research to start developing a system to store diagrams for rapid retrieval and simple modifications. The idea was that the diagrams would be digitized into the computer, displayed interactively to allow rotations, scaling and projections, and then printed on demand. Lookups would be handled via punched card
Punched card
A punched card, punch card, IBM card, or Hollerith card is a piece of stiff paper that contains digital information represented by the presence or absence of holes in predefined positions...
queries, which would allow operators to quickly retrieve documents for manipulation into whatever local format the user needed, and then print it. Repetitive queries could be automated simply by saving the card stack.
Prototype
The Data Processing department had already been experimenting with an IBM 704IBM 704
The IBM 704, the first mass-produced computer with floating point arithmetic hardware, was introduced by IBM in 1954. The 704 was significantly improved over the IBM 701 in terms of architecture as well as implementations which were not compatible with its predecessor.Changes from the 701 included...
computer displaying points on the IBM 780 display which were recorded to 8 mm film. One early use was plotting traffic simulations. However, the displays were not based on storage tube
Storage tube
Mostly obsolete, a storage tube is a special monochromatic CRT whose screen has a kind of 'memory' : when a portion of the screen is illuminated by the CRT's electron gun, it stays lit until a screen erase command is given...
s, so the images disappeared shortly after they were drawn. In order to keep the image on the screen, the program had to be put into a loop, continually refreshing the display. While this was happening the computer could not be used for other tasks. Although it was suitable for demonstration purposes, a real-world system would need additional hardware to offload this task from the CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
.
Another problem was printing the diagrams. GM solved this problem by using an approach developed by Boeing
Boeing
The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...
, replacing the milling head of a computerized milling machine with a ball-point pen and connecting the inputs of the mill to the 704 computer. To address the extremely limited amount of memory available on the 704, they broke the diagrams down into 32-by-32-inch squares, which could be plotted with enough accuracy that they could be loaded up as separate tiles and still line up perfectly when plotted as part of complete diagrams. A set of rollers were added to allow the plotter to move a single 96 inches (2,438.4 mm) piece of paper around the drawing surface on demand, meaning that the paper did not have to be cut into pieces. The paper was delivered in rolls, allowing diagrams to be any length.
The final problem was to convert the existing diagrams, on paper, into computer data. The solution was to re-print the diagrams onto clear acetate and place them in front of the 780 display. The computer then moved the display's dot across the screen, where it would be periodically occluded by the lines on the acetate. A photomultiplier
Photomultiplier
Photomultiplier tubes , members of the class of vacuum tubes, and more specifically phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum...
tube noticed these drops in output and recorded them. Since diagrams consist largely of whitespace and a few lines, a simple raster scan would be too time consuming. Instead, when the program noticed a line it would scan a circle of points around the last hit, attempting to find the line again. The system allowed the digitizing of 6,000 points a second. The output was a set of cubic polynomials that described the line smoothly.
DAC-1
The system, known as Digital Design, was demonstrated and improved throughout 1959. In order to avoid confusion over the term "digital", which at that time was most closely associated with fingers and not computing, the name changed to DAC-1. By the summer it was clear the basic idea was feasible. In August, the team was given the go-ahead to start work with IBM to purchase an IBM 7090IBM 7090
The IBM 7090 was a second-generation transistorized version of the earlier IBM 709 vacuum tube mainframe computers and was designed for "large-scale scientific and technological applications". The 7090 was the third member of the IBM 700/7000 series scientific computers. The first 7090 installation...
computer and develop commercial versions of the display hardware.
The production system had to not only manipulate existing drawings, but also be capable of modifying them in the computer. Although the computer would not normally be used to produce new artwork, once the diagrams were scanned into the system, changes could be made without going through the entire scanning process again.
Once digitized, additional software could be used to convert the lines into a 3D shape. This was groundbreaking research at the time, and generated a flurry of research papers. Once converted, the diagrams could be output into the APT numerical control
Numerical control
Numerical control refers to the automation of machine tools that are operated by abstractly programmed commands encoded on a storage medium, as opposed to controlled manually via handwheels or levers, or mechanically automated via cams alone...
language for direct output on milling machines. This would allow a design team to sketch out their ideas, put them into the system and clean them up, and then have the milling systems produce a physical model.
IBM partnership
In July 1960 IBM presented GM with a formal development contract for a "Graphic Expression Machine", or "Project GEM". The system was hosted by the 7090, IBM's then-standard large business offering, partnered with two new channel controllers for the yet-to-be-released IBM 1301 hard diskHard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
system, and a custom controller to drive multiple graphical terminals. Output from the terminals could be sent to a plotter, 35 mm slide film. IBM estimated the system would be installed within 18 months after signing the contract. GM accepted the offer in November 1960.
Development took longer than expected. While the 7090 was being installed at GM Research in Warren, MI, the GM teams were given use of one of IBM's own 7090s in Kingston, NY. As the original production date grew closer the number of GM employees traveling to NY became a serious budget problem, which was addressed when GM rented a Convair
Convair
Convair was an American aircraft manufacturing company which later expanded into rockets and spacecraft. The company was formed in 1943 by the merger of Vultee Aircraft and Consolidated Aircraft, and went on to produce a number of pioneering aircraft, such as the Convair B-36 bomber, and the F-102...
aircraft for ferry flights between the two sites. A more serious problem was the scanner system, and a joint GM-IBM team was able to finally address the issues.
The system was given a full demonstration run at IBM's Kingston site in December 1962. The demonstrations were so well attended that bleacher
Bleacher
Bleachers is an American term used to describe the raised, tiered rows of seats found at sports fields or at other spectator events...
s were set up so that all of the attendees could see the terminal screen. The high usage demands during the demos eventually led to the disk system crashing. The production DAC-1 system went live in Warren in April 1963. At the time the 1301 was not ready, so a IBM 1401
IBM 1401
The IBM 1401 was a variable wordlength decimal computer that was announced by IBM on October 5, 1959. The first member of the highly successful IBM 1400 series, it was aimed at replacing electromechanical unit record equipment for processing data stored on punched cards...
and IBM 1405 were used instead.
DAC-1 was one of the earliest production CAD systems to enter use, only the Itek
Itek
Itek Corporation was a US defense contractor that initially specialized in the field of camera systems for spy satellites. In the early 1960s they built a conglomerate in a fashion similar to LTV or Litton, during which time they developed the first CAD system and explored optical disk technology...
built Digigraphics
Digigraphics
Digigraphics was one of the first graphical computer aided design systems to go on sale. Originally developed at Itek on the PDP-1 as EDM , the efforts were purchased by Control Data Corporation and ported to their machines, along with a new graphics terminal to support it...
system beat it, albeit to the extent of a single machine before it was taken over by Control Data Corporation
Control Data Corporation
Control Data Corporation was a supercomputer firm. For most of the 1960s, it built the fastest computers in the world by far, only losing that crown in the 1970s after Seymour Cray left the company to found Cray Research, Inc....
.
In November 1963, DAC-1 was used to create a model of a trunk lid in a straight-through manner. An original sketch was read in, cleaned up on the terminal, converted into 3D and then output to a milling machine
Milling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...
.
Alpine
With the successful delivery of DAC-1, IBM turned to commercializing the system in "Project Alpine". The results of Alpine were the IBM 2250IBM 2250
The IBM 2250 Graphics Display Unit was announced as part of System/360 in 1964. Unlike most modern computer displays, which show images in raster format, the IBM 2250 used vector graphics. A display list of line segments on a 1024 by 1024 grid was stored in the computer's memory and repainted on...
graphics terminal, 2280 film recorder and 2281 film scanner. Unlike the DAC-1's 7090, the Alpine products were all aimed for use with the newly announced IBM 360 series of computers. The graphics terminal was quite successful and IBM became a major CAD vendor. The film printer and scanner found little use among customers that were moving to all-digital workflows, and were later withdrawn as supported products.
End of DAC
DAC had always been intended to be a sort of "large area experiment", not a production system. As an experimental system, DAC was extremely successful, but the designers were well aware that additional development would be needed to make it really useful. In 1967 the CAD project was officially ended. By this point IBM had long abandoned the 7090 series for the 360, and was already working on its replacement, the IBM System/370. DAC was moved from Research to Fischer Body, but being outdated it was later donated to the University of Michigan.When polled, team leaders within the project universally pointed to the batch-oriented operating system as the primary impediment to a truly interactive design system, with computer performance and a hierarchical file system as secondary concerns. This led to the MCTS system, "Multi-Console Time Sharing", a version of Multics
Multics
Multics was an influential early time-sharing operating system. The project was started in 1964 in Cambridge, Massachusetts...
adapted for their own use, which they developed on the CDC STAR-100
CDC STAR-100
The STAR-100 was a vector supercomputer designed, manufactured, and marketed by Control Data Corporation . It was one of the first machines to use a vector processor to improve performance on appropriate scientific applications....
computer.
Operating system
The DAC-1 system included its own custom operating systemOperating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
, known, as was typical at the time, simply as "monitor". Monitor was based on the earlier batch processing systems developed at GM and IBM, but fed in the batches not from punched cards, but from the attached channel controllers instead. Terminals that had to exchange information with the host computer would place data in the controller for relay, which would cause an interrupt. The host machine would service the interrupt by copying the data from the terminal into the batch monitor, which would run it as if the input had come from a card stack. The DAC program consisted of a variety of small programs which were called by the batch monitor. Their output was then copied back to the terminals as if they were printers. Users who were not actively interacting with the terminals at any given time automatically gave up their time to other users. Although the term was not in widespread use at the time, the DAC-1 system was thus an early example of a time-sharing system.
Unlike traditional batch systems, where operators manually scheduled workflows for fastest possible access to resources, DAC-1's workload would be unpredictable. This led to potential situations where one request could take a device offline for servicing, changing tapes for instance, only to have the next request data from that device. Although no general solution to the problem was found, the programmers invested considerable effort in ensuring that all of the modules needed for a particular operation could be loaded in a single "clump".
The original 7090 had a single 32 kbyte bank of memory. In order to improve performance, the DAC-1 software was left in the core, isolated in one of two 16 kbyte logical banks. The other 16 kbytes held the batch monitor and an interrupt controller that drove it. With the introduction of the 7094, the two programs were separated into their own 32 kbyte physical stores. This left little room for user programs and data. After the DAC-1 was first installed, the original 7090 was relegated to other tasks and was replaced by an IBM 7094-II. In addition to being faster, this machine was equipped with two 32 kbyte core memory stores, an unusual arrangement. The two banks allowed DAC to have an entire 32 kbytes to itself.
Programming
Programming on the DAC system was in IBM's FORTRAN IV compiler, but it quickly became clear that a language with graphics primitives would be highly desirable. GM started with an existing ALGOL 58ALGOL 58
ALGOL 58, originally known as IAL, is one of the family of ALGOL computer programming languages. It was an early compromise design soon superseded by ALGOL 60...
derivative from the University of Michigan
University of Michigan
The University of Michigan is a public research university located in Ann Arbor, Michigan in the United States. It is the state's oldest university and the flagship campus of the University of Michigan...
, MAD (Michigan Algorithm Decoder), adding to it and creating their own version, NOMAD. NOMAD also included the ability to allow code to run anywhere in memory, which was very important, especially on the earlier machine with limited memory. Over 90% of the DAC system was written in NOMAD.
A similar language was also developed for the special task of running on the channel controllers. The new language was named "Maybe", because it was not clear whether or not it would work. Maybe turned into a joint effort between GM and the University of Michigan, and was indeed used on the production system.
The DAC-1 system also included a custom language intended for the users, not the programmers. DGL, for descriptive geometry language" was a simple domain-specific language that contained a number of basic geometrical operators and variable assignment. Users could write programs in DGL and input them into DAC using punched cards. The result were new modules that the user could call within the interactive environment.
Terminals
DAC had been designed with a workflow in mind; paper and pencil sketching, digitizing on the reader, minor manipulation on the terminals, and then printing or modeling. In spite of it being the centerpiece of the operation, the graphics terminal was given little thought during the design process. Performance issues limited diagrams to about 1,000 vectors; at this point the refresh time became so slow the display would become difficult to use due to flickering.The IBM design used a capacitance screen
Touchscreen
A touchscreen is an electronic visual display that can detect the presence and location of a touch within the display area. The term generally refers to touching the display of the device with a finger or hand. Touchscreens can also sense other passive objects, such as a stylus...
with a metal pencil for input, providing a directly read X and Y coordinate. The basic system was similar to modern touch screen systems like the iPhone
IPhone
The iPhone is a line of Internet and multimedia-enabled smartphones marketed by Apple Inc. The first iPhone was unveiled by Steve Jobs, then CEO of Apple, on January 9, 2007, and released on June 29, 2007...
, but not sensitive enough to detect a finger and instead required a wired conductor to complete the circuit. The pencil replaced the light pens because it was much faster to decode; a light pen had to wait for a pulse of light when a vector was being redrawn and then work its way through the list of vectors to find out which one was selected.
In use it was quickly discovered that holding the pen to the vertical monitor screen was extremely tiring, so the idea of using the terminal for input was abandoned. The GM team later visited Douglas Engelbart
Douglas Engelbart
Douglas Carl Engelbart is an American inventor, and an early computer and internet pioneer. He is best known for his work on the challenges of human-computer interaction, resulting in the invention of the computer mouse, and the development of hypertext, networked computers, and precursors to GUIs...
's lab where they saw the first computer mouse, and based future projects on this device instead.
All of the terminals were connected to a single controller, and in turn to the 7090 via its Channel C input. Channel A and B were used to control magnetic tape
Magnetic tape
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...
drives, and Channel D controlled the 1301 disk.
Further reading
- GM's Road to Virtual Product Development, contains images and videos of DAC-1