77-679: PETSCII ( PET Standard Code of Information Interchange ), also known as CBM ASCII , is the character set used in Commodore Business Machines' 8-bit home computers . This character set was first used by the PET from 1977, and was subsequently used by the CBM-II , VIC-20 , Commodore 64 , Commodore 16 , Commodore 116 , Plus/4 , and Commodore 128 . However, the Amiga personal computer family instead uses standard ISO/IEC 8859-1 . The character set
154-402: A byte order mark or escape sequences ; compressing schemes try to minimize the number of bytes used per code unit (such as SCSU and BOCU ). Although UTF-32BE and UTF-32LE are simpler CESes, most systems working with Unicode use either UTF-8 , which is backward compatible with fixed-length ASCII and maps Unicode code points to variable-length sequences of octets, or UTF-16BE , which
231-434: A graphics library such as OpenGL or Direct3D which interfaces with the graphics driver to translate received commands to instructions for the accelerator's graphics processing unit (GPU). The GPU uses those instructions to compute the rasterized results and the results are bit blitted to the framebuffer. The framebuffer's signal is then produced in combination with built-in video overlay devices (usually used to produce
308-437: A string of the letters "ab̲c𐐀"—that is, a string containing a Unicode combining character ( U+0332 ̲ COMBINING LOW LINE ) as well as a supplementary character ( U+10400 𐐀 DESERET CAPITAL LETTER LONG I ). This string has several Unicode representations which are logically equivalent, yet while each is suited to a diverse set of circumstances or range of requirements: Note in particular that 𐐀
385-759: A "Base 128" encoding is in DATA statements in Commodore BASIC. Binary data can be stored with relatively low overhead, allowing one character of data to encode seven bits of data. On a standard 80-character line, typically four characters are used for the line number, and two characters for the tokenized DATA statement. Since the comma and colon are significant to BASIC, a quote character is also needed, leaving 73 characters for data. At seven bits per character, one DATA line could store 511 bits of binary data, for 79% efficiency. If three-digit line numbers are used, efficiency increases to 80%. If two-digit line numbers are used, efficiency
462-503: A "shifted" mode (also called "business mode"), which changes the uppercase letters at 0x41–0x5A to lowercase, and changes the graphics at 0xC1–0xDA to uppercase letters. Upper- and lower-case are swapped from where ASCII has them. The mode is toggled by holding one of the SHIFT keys and then pressing and releasing the Commodore key. The shift can be done by POKEing location 59468 with
539-528: A 4096 display in 1950. A color scanned display was implemented in the late 1960s, called the Brookhaven RAster Display (BRAD), which used a drum memory and a television monitor. In 1969, A. Michael Noll of Bell Labs implemented a scanned display with a frame buffer, using magnetic-core memory . Later on, the Bell Labs system was expanded to display an image with a color depth of three bits on
616-464: A boon for graphics researchers who did not have the resources to build their own framebuffer. The New York Institute of Technology would later create the first 24-bit color system using three of the Evans & Sutherland framebuffers. Each framebuffer was connected to an RGB color output (one for red, one for green and one for blue), with a Digital Equipment Corporation PDP 11/04 minicomputer controlling
693-424: A higher quality than on home computers. Framebuffers used in personal and home computing often had sets of defined modes under which the framebuffer can operate. These modes reconfigure the hardware to output different resolutions, color depths, memory layouts and refresh rate timings. In the world of Unix machines and operating systems, such conveniences were usually eschewed in favor of directly manipulating
770-677: A left-arrow ⟨←⟩ instead of an underscore ⟨_⟩ at 0x5F. In all versions except the original Commodore PET, it also has a British pound sign ⟨£⟩ instead of the backslash ⟨\⟩ at 0x5C. Other characters added in ASCII-1967 (lowercase letters, the grave accent , curly braces , vertical bar, and tilde) do not exist in PETSCII. Codes 0xA0–0xDF are allotted to CBM-specific block graphics characters —horizontal and vertical lines, hatches, shades, triangles, circles and card suits . PETSCII also has
847-420: A particular sequence of bits. Instead, characters would first be mapped to a universal intermediate representation in the form of abstract numbers called code points . Code points would then be represented in a variety of ways and with various default numbers of bits per character (code units) depending on context. To encode code points higher than the length of the code unit, such as above 256 for eight-bit units,
SECTION 10
#1732851655809924-399: A process known as transcoding . Some of these are cited below. Cross-platform : Windows : The most used character encoding on the web is UTF-8 , used in 98.2% of surveyed web sites, as of May 2024. In application programs and operating system tasks, both UTF-8 and UTF-16 are popular options. Framebuffer A framebuffer ( frame buffer , or sometimes framestore )
1001-411: A rectangle of swatches): In some designs it was also possible to write data to the lookup table (or switch between existing palettes) on the fly, allowing dividing the picture into horizontal bars with their own palette and thus render an image that had a far wider palette. For example, viewing an outdoor shot photograph, the picture could be divided into four bars, the top one with emphasis on sky tones,
1078-461: A single glyph . The former simplifies the text handling system, but the latter allows any letter/diacritic combination to be used in text. Ligatures pose similar problems. Exactly how to handle glyph variants is a choice that must be made when constructing a particular character encoding. Some writing systems, such as Arabic and Hebrew, need to accommodate things like graphemes that are joined in different ways in different contexts, but represent
1155-546: A single character per code unit. However, due to the emergence of more sophisticated character encodings, the distinction between these terms has become important. "Code page" is a historical name for a coded character set. Originally, a code page referred to a specific page number in the IBM standard character set manual, which would define a particular character encoding. Other vendors, including Microsoft , SAP , and Oracle Corporation , also published their own sets of code pages;
1232-407: A standard color TV monitor. In the early 1970s, the development of MOS memory ( metal–oxide–semiconductor memory) integrated-circuit chips, particularly high-density DRAM (dynamic random-access memory ) chips with at least 1 kb memory, made it practical to create, for the first time, a digital memory system with framebuffers capable of holding a standard video image. This led to
1309-432: A stream of octets (bytes). The purpose of this decomposition is to establish a universal set of characters that can be encoded in a variety of ways. To describe this model precisely, Unicode uses its own set of terminology to describe its process: An abstract character repertoire (ACR) is the full set of abstract characters that a system supports. Unicode has an open repertoire, meaning that new characters will be added to
1386-424: A technique known generally as double buffering or more specifically as page flipping , the framebuffer uses half of its memory to display the current frame. While that memory is being displayed, the other half of memory is filled with data for the next frame. Once the secondary buffer is filled, the framebuffer is instructed to display the secondary buffer instead. The primary buffer becomes the secondary buffer, and
1463-505: A well-defined and extensible encoding system, has replaced most earlier character encodings, but the path of code development to the present is fairly well known. The Baudot code, a five- bit encoding, was created by Émile Baudot in 1870, patented in 1874, modified by Donald Murray in 1901, and standardized by CCITT as International Telegraph Alphabet No. 2 (ITA2) in 1930. The name baudot has been erroneously applied to ITA2 and its many variants. ITA2 suffered from many shortcomings and
1540-473: Is backward compatible with fixed-length UCS-2BE and maps Unicode code points to variable-length sequences of 16-bit words. See comparison of Unicode encodings for a detailed discussion. Finally, there may be a higher-level protocol which supplies additional information to select the particular variant of a Unicode character, particularly where there are regional variants that have been 'unified' in Unicode as
1617-435: Is 82%. For storing binary data in Commodore BASIC, it appears that two- or three-digit line numbers are typically the best choice. 164 PETSCII characters are representable in quoted strings; theoretically, then, Base 164 is possible. This adds in the color values, the function keys, and cursor controls. Character encoding Character encoding is the process of assigning numbers to graphical characters , especially
SECTION 20
#17328516558091694-467: Is a part of computer memory used by a computer application for the representation of the content to be shown on the computer display . The screen buffer may also be called the video buffer , the regeneration buffer , or regen buffer for short. Screen buffers should be distinguished from video memory . To this end, the term off-screen buffer is also used. The information in the buffer typically consists of color values for every pixel to be shown on
1771-409: Is a portion of random-access memory (RAM) containing a bitmap that drives a video display. It is a memory buffer containing data representing all the pixels in a complete video frame . Modern video cards contain framebuffer circuitry in their cores. This circuitry converts an in-memory bitmap into a video signal that can be displayed on a computer monitor. In computing , a screen buffer
1848-442: Is defined by a CEF. A character encoding scheme (CES) is the mapping of code units to a sequence of octets to facilitate storage on an octet-based file system or transmission over an octet-based network. Simple character encoding schemes include UTF-8 , UTF-16BE , UTF-32BE , UTF-16LE , and UTF-32LE ; compound character encoding schemes, such as UTF-16 , UTF-32 and ISO/IEC 2022 , switch between several simple schemes by using
1925-444: Is defined by the encoding. Thus, the number of code units required to represent a code point depends on the encoding: Exactly what constitutes a character varies between character encodings. For example, for letters with diacritics , there are two distinct approaches that can be taken to encode them: they can be encoded either as a single unified character (known as a precomposed character), or as separate characters that combine into
2002-430: Is preferred, usually in the larger context of locales. IBM's Character Data Representation Architecture (CDRA) designates entities with coded character set identifiers ( CCSIDs ), each of which is variously called a "charset", "character set", "code page", or "CHARMAP". The code unit size is equivalent to the bit measurement for the particular encoding: A code point is represented by a sequence of code units. The mapping
2079-492: Is represented with either one 32-bit value (UTF-32), two 16-bit values (UTF-16), or four 8-bit values (UTF-8). Although each of those forms uses the same total number of bits (32) to represent the glyph, it is not obvious how the actual numeric byte values are related. As a result of having many character encoding methods in use (and the need for backward compatibility with archived data), many computer programs have been developed to translate data between character encoding schemes,
2156-407: Is that a full range of colors cannot be produced. The solution to this problem was indexed color , which adds a lookup table to the framebuffer. Each color stored in framebuffer memory acts as a color index. The lookup table serves as a palette with a limited number of different colors, while the rest is used as an index table. Here is a typical indexed 256-color image and its own palette (shown as
2233-640: The Symbols for Legacy Computing block. The following tables represent the PETSCII encoding used on the Commodore VIC-20, 64, 16, and 128. While the graphic characters were mostly shared between Commodore systems, the control characters frequently varied. The follow table describes what the control characters represent on the Commodore PET 2001 , Commodore PET 8032 , VIC-20 , Commodore 64 , Commodore 16 , Commodore 128 (40 and 80 column modes). The colors of
2310-597: The World Wide Web is UTF-8 , which is used in 98.2% of surveyed web sites, as of May 2024. In application programs and operating system tasks, both UTF-8 and UTF-16 are popular options. The history of character codes illustrates the evolving need for machine-mediated character-based symbolic information over a distance, using once-novel electrical means. The earliest codes were based upon manual and hand-written encoding and cyphering systems, such as Bacon's cipher , Braille , international maritime signal flags , and
2387-482: The 1980s faced the dilemma that, on the one hand, it seemed necessary to add more bits to accommodate additional characters, but on the other hand, for the users of the relatively small character set of the Latin alphabet (who still constituted the majority of computer users), those additional bits were a colossal waste of then-scarce and expensive computing resources (as they would always be zeroed out for such users). In 1985,
PETSCII - Misplaced Pages Continue
2464-409: The 1980s. SGI , Sun Microsystems , HP , DEC and IBM all released framebuffers for their workstation computers in this period. These framebuffers were usually of a much higher quality than could be found in most home computers, and were regularly used in television, printing, computer modeling and 3D graphics. Framebuffers were also used by Sega for its high-end arcade boards , which were also of
2541-532: The 4-digit encoding of Chinese characters for a Chinese telegraph code ( Hans Schjellerup , 1869). With the adoption of electrical and electro-mechanical techniques these earliest codes were adapted to the new capabilities and limitations of the early machines. The earliest well-known electrically transmitted character code, Morse code , introduced in the 1840s, used a system of four "symbols" (short signal, long signal, short space, long space) to generate codes of variable length. Though some commercial use of Morse code
2618-457: The Commodore VIC-20, 64, 16, and 128 they duplicate 0xC0–0xDF and 0xA0–0xBF, respectively. While these characters are visually duplicates, they are semantically different; for example, on the Commodore PET, code points 0x2C and 0x6C both produce a comma character, but only 0x2C functions as a delimiter between input fields. Graphic characters are mostly identical across systems, with
2695-486: The LCD must digitally sample the display signal (thereby emulating an electron beam), any signal that is out of range cannot be physically displayed on the monitor. Framebuffers have traditionally supported a wide variety of color modes. Due to the expense of memory, most early framebuffers used 1-bit (2 colors per pixel), 2-bit (4 colors), 4-bit (16 colors) or 8-bit (256 colors) color depths. The problem with such small color depths
2772-517: The SuperPaint system to produce a wide variety of colors outside the range of the limited 8-bit data it contained. This scheme would later become commonplace in computer framebuffers. In 1974, Evans & Sutherland released the first commercial framebuffer, the Picture System, costing about $ 15,000. It was capable of producing resolutions of up to 512 by 512 pixels in 8-bit grayscale , and became
2849-509: The Unicode standard is U+0000 to U+10FFFF, inclusive, divided in 17 planes , identified by the numbers 0 to 16. Characters in the range U+0000 to U+FFFF are in plane 0, called the Basic Multilingual Plane (BMP). This plane contains the most commonly-used characters. Characters in the range U+10000 to U+10FFFF in the other planes are called supplementary characters . The following table shows examples of code point values: Consider
2926-572: The VIC's 22-column screen. The Commodore 64, however, used a slightly re-designed, heavy upper-case font, essentially a thicker version of the PET's, in order to avoid color artifacts created by the machine's higher resolution screen. The C64's lowercase characters are identical to the lowercase characters in the Atari 8-bit computers font (released 2.75 years earlier). Peddle claims the inclusion of card suit symbols
3003-523: The VIC-20 and C64/128 are listed in the VIC-II article. Out of PETSCII's first 192 codes, there are 128 graphic characters: 32–127 and 160–192. This permits "base128"-style encodings in DATA statements, or perhaps between PETSCII-speaking machines. This can also include control characters, which are visible when quoted, although which control characters are defined varies between systems. The primary application for
3080-573: The X Virtual Framebuffer ( Xvfb ). Xvfb was added to the X Window System distribution to provide a method for running X without a graphical framebuffer. The Linux framebuffer device was developed to abstract the physical method for accessing the underlying framebuffer into a guaranteed memory map that is easy for programs to access. This increases portability, as programs are not required to deal with systems that have disjointed memory maps or require bank switching . A frame buffer may be designed with enough memory to store two frames worth of video data. In
3157-464: The average personal computer user's hard disk drive could store only about 10 megabytes, and it cost approximately US$ 250 on the wholesale market (and much higher if purchased separately at retail), so it was very important at the time to make every bit count. The compromise solution that was eventually found and developed into Unicode was to break the assumption (dating back to telegraph codes) that each character should always directly correspond to
PETSCII - Misplaced Pages Continue
3234-408: The codes using their actual names in curly braces, like the above examples. This is unambiguous as PETSCII has no curly brace characters. Different mappings are used for storing characters (the "interchange" mapping, as used by CHR$ () ) and displaying characters (the "video" mapping). For example, to display the characters "@ABC" on screen by directly writing into the screen memory , one would POKE
3311-440: The decimal values 0, 1, 2, and 3 rather than 64, 65, 66, and 67. The keyboard by default provides access to the lower half of the code page. Pressing Shift and a key gives the corresponding upper half code point. Some PETSCII code points cannot be printed and are only used for keyboard input (e.g. F1, RUN/STOP). The tables below represent the "interchange" PETSCII encoding, as used by CHR$ () . Control characters are defined in
3388-462: The development of the SuperPaint system by Richard Shoup at Xerox PARC in 1972. Shoup was able to use the SuperPaint framebuffer to create an early digital video-capture system. By synchronizing the output signal to the input signal, Shoup was able to overwrite each pixel of data as it shifted in. Shoup also experimented with modifying the output signal using color tables. These color tables allowed
3465-455: The display. Color values are commonly stored in 1-bit binary (monochrome), 4-bit palettized , 8-bit palettized, 16-bit high color and 24-bit true color formats. An additional alpha channel is sometimes used to retain information about pixel transparency. The total amount of memory required for the framebuffer depends on the resolution of the output signal, and on the color depth or palette size. Computer researchers had long discussed
3542-536: The era had their own character codes, often six-bit, but usually had the ability to read tapes produced on IBM equipment. These BCD encodings were the precursors of IBM's Extended Binary-Coded Decimal Interchange Code (usually abbreviated as EBCDIC), an eight-bit encoding scheme developed in 1963 for the IBM System/360 that featured a larger character set, including lower case letters. In trying to develop universally interchangeable character encodings, researchers in
3619-529: The exceptions of 0x5C (which is \ on the Commodore PET, and £ on other systems), 0xDE (which is U+1FB95 CHECKER BOARD FILL on the Commodore PET and VIC-20, and U+1FB96 INVERSE CHECKER BOARD FILL on other systems), and the range 0x60–0x7F (which duplicates a different range on Commodore PET). Additionally, in Commodore PET 2001 's shifted character set, uppercase and lowercase letters are swapped relative to other systems'. Compatibility symbols for PETSCII characters were added to Unicode 13.0 as part of
3696-444: The framebuffer during the scan, creating a set of discrete picture elements, i.e. pixels. Framebuffers differ significantly from the vector displays that were common prior to the advent of raster graphics (and, consequently, to the concept of a framebuffer). With a vector display, only the vertices of the graphics primitives are stored. The electron beam of the output display is then commanded to move from vertex to vertex, tracing
3773-558: The framebuffer. This is commonly called graphics acceleration . Common graphics drawing commands (many of them geometric) are sent to the graphics accelerator in their raw form. The accelerator then rasterizes the results of the command to the framebuffer. This method frees the CPU to do other work. Early accelerators focused on improving the performance of 2D GUI systems. While retaining these 2D capabilities, most modern accelerators focus on producing 3D imagery in real time. A common design uses
3850-477: The hardware settings. This manipulation was far more flexible in that any resolution, color depth and refresh rate was attainable – limited only by the memory available to the framebuffer. An unfortunate side-effect of this method was that the display device could be driven beyond its capabilities. In some cases, this resulted in hardware damage to the display. More commonly, it simply produced garbled and unusable output. Modern CRT monitors fix this problem through
3927-472: The home computers of the late 1970s to contain low-color-depth framebuffers. Today, nearly all computers with graphical capabilities utilize a framebuffer for generating the video signal. Amiga computers, created in the 1980s, featured special design attention to graphics performance and included a unique Hold-And-Modify framebuffer capable of displaying 4096 colors. Framebuffers also became popular in high-end workstations and arcade system boards throughout
SECTION 50
#17328516558094004-459: The introduction of protection circuitry. When the display mode is changed, the monitor attempts to obtain a signal lock on the new refresh frequency. If the monitor is unable to obtain a signal lock, or if the signal is outside the range of its design limitations, the monitor will ignore the framebuffer signal and possibly present the user with an error message. LCD monitors tend to contain similar protection circuitry, but for different reasons. Since
4081-412: The market for graphics accelerators for x86-based systems is dominated by Nvidia (acquired 3dfx in 2002), AMD (who acquired ATI in 2006), and Intel . With a framebuffer, the electron beam (if the display technology uses one) is commanded to perform a raster scan , the way a television renders a broadcast signal. The color information for each point thus displayed on the screen is pulled directly from
4158-484: The methods used to access memory. Some of the most common are: The framebuffer organization may be packed pixel or planar . The framebuffer may be all points addressable or have restrictions on how it can be updated. Video cards always have a certain amount of RAM. A small portion of this RAM is where the bitmap of image data is "buffered" for display. The term frame buffer is thus often used interchangeably when referring to this RAM. The CPU sends image updates to
4235-475: The most well-known code page suites are " Windows " (based on Windows-1252) and "IBM"/"DOS" (based on code page 437 ). Despite no longer referring to specific page numbers in a standard, many character encodings are still referred to by their code page number; likewise, the term "code page" is often still used to refer to character encodings in general. The term "code page" is not used in Unix or Linux, where "charmap"
4312-581: The mouse cursor without modifying the framebuffer's data) and any final special effects that are produced by modifying the output signal. An example of such final special effects was the spatial anti-aliasing technique used by the 3dfx Voodoo cards. These cards add a slight blur to the output signal that makes aliasing of the rasterized graphics much less obvious. At one time there were many manufacturers of graphics accelerators, including: 3dfx Interactive ; ATI ; Hercules ; Trident ; Nvidia ; Radius ; S3 Graphics ; SiS and Silicon Graphics . As of 2015
4389-402: The next with foliage tones, the next with skin and clothing tones, and the bottom one with ground colors. This required each palette to have overlapping colors, but carefully done, allowed great flexibility. While framebuffers are commonly accessed via a memory mapping directly to the CPU memory space, this is not the only method by which they may be accessed. Framebuffers have varied widely in
4466-412: The punched card code then in use only allowed digits, upper-case English letters and a few special characters, six bits were sufficient. These BCD encodings extended existing simple four-bit numeric encoding to include alphabetic and special characters, mapping them easily to punch-card encoding which was already in widespread use. IBM's codes were used primarily with IBM equipment; other computer vendors of
4543-480: The ranges 0x00–0x1F and 0x80–0x9F, although which control characters are defined and what they are defined as varies between systems. The tables below exclude control characters—the encoding of control characters in discussed in § Control characters . The ranges 0x60–0x7F and 0xE0–0xFF are duplicate ranges, although what they duplicate varies between systems. On the Commodore PET, they duplicate 0x20–0x3F and 0xA0–0xBF, respectively; on
4620-460: The repertoire over time. A coded character set (CCS) is a function that maps characters to code points (each code point represents one character). For example, in a given repertoire, the capital letter "A" in the Latin alphabet might be represented by the code point 65, the character "B" by 66, and so on. Multiple coded character sets may share the same character repertoire; for example ISO/IEC 8859-1 and IBM code pages 037 and 500 all cover
4697-491: The same character. An example is the XML attribute xml:lang. The Unicode model uses the term "character map" for other systems which directly assign a sequence of characters to a sequence of bytes, covering all of the CCS, CEF and CES layers. In Unicode, a character can be referred to as 'U+' followed by its codepoint value in hexadecimal. The range of valid code points (the codespace) for
SECTION 60
#17328516558094774-537: The same repertoire but map them to different code points. A character encoding form (CEF) is the mapping of code points to code units to facilitate storage in a system that represents numbers as bit sequences of fixed length (i.e. practically any computer system). For example, a system that stores numeric information in 16-bit units can only directly represent code points 0 to 65,535 in each unit, but larger code points (say, 65,536 to 1.4 million) could be represented by using multiple 16-bit units. This correspondence
4851-522: The same semantic character. Unicode and its parallel standard, the ISO/IEC 10646 Universal Character Set , together constitute a unified standard for character encoding. Rather than mapping characters directly to bytes , Unicode separately defines a coded character set that maps characters to unique natural numbers ( code points ), how those code points are mapped to a series of fixed-size natural numbers (code units), and finally how those units are encoded as
4928-416: The secondary buffer becomes the primary. This switch is often done after the vertical blanking interval to avoid screen tearing where half the old frame and half the new frame is shown together. Page flipping has become a standard technique used by PC game programmers . As the demand for better graphics increased, hardware manufacturers created a way to decrease the amount of CPU time required to fill
5005-433: The solution was to implement variable-length encodings where an escape sequence would signal that subsequent bits should be parsed as a higher code point. Informally, the terms "character encoding", "character map", "character set" and "code page" are often used interchangeably. Historically, the same standard would specify a repertoire of characters and how they were to be encoded into a stream of code units — usually with
5082-538: The theoretical advantages of a framebuffer but were unable to produce a machine with sufficient memory at an economically practicable cost. In 1947, the Manchester Baby computer used a Williams tube , later the Williams-Kilburn tube, to store 1024 bits on a cathode-ray tube (CRT) memory and displayed on a second CRT. Other research labs were exploring these techniques with MIT Lincoln Laboratory achieving
5159-634: The three devices as one. In 1975, the UK company Quantel produced the first commercial full-color broadcast framebuffer, the Quantel DFS 3000. It was first used in TV coverage of the 1976 Montreal Olympics to generate a picture-in-picture inset of the Olympic flaming torch while the rest of the picture featured the runner entering the stadium. The rapid improvement of integrated-circuit technology made it possible for many of
5236-878: The value 14 to select the alternative set or 12 to revert to standard. On the Commodore 64, the sets are alternated by flipping bit 2 of the byte 53272. On some models of PET, this can also be achieved via special control code PRINT CHR$ (14) which adjust the line spacing as well as changing the character set; the POKE method is still available and does not alter the line spacing. Included in PETSCII are cursor and screen control codes, such as {HOME} , {CLR} , {RVS ON} , and {RVS OFF} (the latter two activating/deactivating reverse-video character display). The control codes appeared in program listings as reverse-video graphic characters, although some computer magazines, in their efforts to provide more clearly readable listings, pretty-printed
5313-514: The video card. The video processor on the card forms a picture of the screen image and stores it in the frame buffer as a large bitmap in RAM. The bitmap in RAM is used by the card to continually refresh the screen image. Many systems attempt to emulate the function of a framebuffer device, often for reasons of compatibility. The two most common virtual framebuffers are the Linux framebuffer device (fbdev) and
5390-697: The written characters of human language, allowing them to be stored, transmitted, and transformed using computers. The numerical values that make up a character encoding are known as code points and collectively comprise a code space, a code page , or character map . Early character codes associated with the optical or electrical telegraph could only represent a subset of the characters used in written languages , sometimes restricted to upper case letters , numerals and some punctuation only. The advent of digital computer systems allows more elaborate encodings codes (such as Unicode ) to support hundreds of written languages. The most popular character encoding on
5467-504: Was adopted fairly widely. ASCII67's American-centric nature was somewhat addressed in the European ECMA-6 standard. Herman Hollerith invented punch card data encoding in the late 19th century to analyze census data. Initially, each hole position represented a different data element, but later, numeric information was encoded by numbering the lower rows 0 to 9, with a punch in a column representing its row number. Later alphabetic data
5544-667: Was encoded by allowing more than one punch per column. Electromechanical tabulating machines represented date internally by the timing of pulses relative to the motion of the cards through the machine. When IBM went to electronic processing, starting with the IBM 603 Electronic Multiplier, it used a variety of binary encoding schemes that were tied to the punch card code. IBM used several Binary Coded Decimal ( BCD ) six-bit character encoding schemes, starting as early as 1953 in its 702 and 704 computers, and in its later 7000 Series and 1400 series , as well as in associated peripherals. Since
5621-432: Was largely designed by Leonard Tramiel (the son of Commodore CEO Jack Tramiel ) and PET designer Chuck Peddle . The graphic characters of PETSCII were one of the extensions Commodore specified for Commodore BASIC when laying out desired changes to Microsoft's existing 6502 BASIC to Microsoft's Ric Weiland in 1977. The VIC-20 used the same pixel-for-pixel font as the PET, although the characters appeared wider due to
5698-409: Was often improved by many equipment manufacturers, sometimes creating compatibility issues. In 1959 the U.S. military defined its Fieldata code, a six-or seven-bit code, introduced by the U.S. Army Signal Corps. While Fieldata addressed many of the then-modern issues (e.g. letter and digit codes arranged for machine collation), it fell short of its goals and was short-lived. In 1963 the first ASCII code
5775-582: Was released (X3.4-1963) by the ASCII committee (which contained at least one member of the Fieldata committee, W. F. Leubbert), which addressed most of the shortcomings of Fieldata, using a simpler code. Many of the changes were subtle, such as collatable character sets within certain numeric ranges. ASCII63 was a success, widely adopted by industry, and with the follow-up issue of the 1967 ASCII code (which added lower-case letters and fixed some "control code" issues) ASCII67
5852-412: Was spurred by the demand that it should be easy to write card games on the PET (as part of the specification list he received). "Unshifted" PETSCII is based on the 1963 version of ASCII (rather than the 1967 version, which most if not all other computer character sets based on ASCII use). It has only uppercase letters, an up-arrow ⟨↑⟩ instead of caret ⟨^⟩ at 0x 5E and
5929-576: Was via machinery, it was often used as a manual code, generated by hand on a telegraph key and decipherable by ear, and persists in amateur radio and aeronautical use. Most codes are of fixed per-character length or variable-length sequences of fixed-length codes (e.g. Unicode ). Common examples of character encoding systems include Morse code, the Baudot code , the American Standard Code for Information Interchange (ASCII) and Unicode. Unicode,
#808191