Regularity
From Maze
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== The Computer Screen == | == The Computer Screen == | ||
| − | [Include the C64 screen 40 x 25 grid] | + | == The Computer Screen == |
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| + | The Commodore 64, economically and conveniently, hooked to an ordinary television. It was an idea that could be seen in Steve Wozniak's Apple I, introduced in April 1976, and the later and more widespread Apple II. That was the main precedent in home computing, but the idea was not original to Apple. At Atari, television engineer and employee #1 Al Alcorn had designed a ''Pong'' cabinet that, rather than using an expensive commercial CRT, incorporated an ordinary black-and-white television that was initially bought from a retail store. Wozniak, who did the original design for the Atari arcade game Breakout, knew about this trick. | ||
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| + | The rectangular form of the television image had its origins in the movie screen, which was rectangular due to the material nature of film and apparently obtained its original 4:3 aspect ratio thanks to a gesture by Thomas Edison, one which resulted in a frame that was four perforations high. While the aspect ratio of film changed and diversified over the years, television in the United States (standardized in the NTSC format in 1953) and many computer monitors, through the 1980s and 1990s, used the 4:3 ratio. | ||
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| + | Although composite monitors were available for the Commodore 46, the relationship between that system and the television was clear and was the default for those setting up their computer and hooking it up to a display. For a Commodore 64 purchased in the United States, the system's video output usually terminated in a NTSC television. But the display did not begin there: It has a heritage that included at least two more unusual output methods. | ||
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| + | As one of us has written, "Early interaction with computers happened largely on paper: on paper tape, on punch cards, and on print terminals and teletypewriters, with their scroll-like supplies of continuous paper for printing output and input both" (Montfort 2004). The standard output devices for computers through much of the 1970s were print terminals and teletypes. Output was not typically produced on pages of the sort that come from today's laser printers, but on scrolls of standard or thermal paper. The form factor for such output was not a standard 8 1/2" x 11" page, but an essentially endless scroll that was typically 80 columns wide. | ||
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| + | Teletypes were used to present the results of BASIC programs that were first written at Dartmouth in the 1960s, and they were the typical means of interacting with important early programs such as Eliza and Adventure. With such a system for output, there was no need for an automated system of "scrollback" -- a user could actually pick up the scroll of output and look at it. Of course, animation and other effects specific to video were also impossible. | ||
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| + | An argument has been advanced that the modern computer screen also has an important heritage in the round CRT display of the radar screen (Gere 2006). The SAGE early warning system, the PDP-1, and the system on which Douglas Engelbart did the "mother of all demos" all sported round cathode ray tubes (CRTs), as did early televisions. It's notable that the first two systems which may have been video games in the modern sense, Tennis for Two by William Higinbotham and Spacewar by Steve Russel et al., were both created for circular CRT displays. While radar and some other images were actually round, as the early cathode ray tube was, the television signal and the page were not. What was, for radar, a radial display eventually gave way in computing to the rectangular, grid format that was adhered to by both page and television image. | ||
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| + | The Commodore 64's video image is a grid 320 pixels wide and 200 pixels tall. This accommodates an array of characters or, in the terminology of Commodore 64 hi res graphics, attribute cells. Specifically, the grid is 40 attribute cells wide and 25 high. (There are other graphics modes that offer advantages, but for understanding 10 PRINT, the array of characters or attribute cells is most important.) Interestingly, the 40x25 grid contains exactly 1000 characters, each represented by a byte. This fits nicely into one kilobyte, 1024 bytes -- in fact, it is the largest grid of 40 characters that occupies 1024 bytes or less. | ||
= Repeating: Regularity in Time and Process = | = Repeating: Regularity in Time and Process = | ||
