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List of home computers by video hardware - Wikipedia, the free encyclopedia

List of home computers by video hardware

From Wikipedia, the free encyclopedia

This is a list of home computers, sorted alphanumerically, which lists all relevant details of their Video Hardware.

A home computer was the description of the second generation of desktop computers, entering the market in 1977 and becoming common during the 1980s. A decade later they were generally replaced by what are now called PCs, although in actuality home computers are also members of the class known as personal computers.

Examples of typical early home computers are the BBC Micro the ZX Spectrum, the MSX 1, the Amstrad CPC 464 and the Commodore 64. Examples of typical late home computers are MSX 2 systems, and the Amiga and Atari ST systems.

Note: in cases of manufacturers who have made both home and personal computers, only machines fitting into the home computer category are listed. These systems, except for Early Macintosh personal computers, are generally all based on the VGA standard, and use a video chip known as as a Graphics processing unit. Although very early PCs used one of the much simpler (even compared to most home computer video hardware) video display controller cards, using standards such as the MDA, Hercules Graphics Card, CGA and EGA standard). Only after the introduction of the VGA standard could PCs really compete with the home computers of the same era, such as the Amiga and Atari ST, or even the MSX-2.

A typical Home computer, an Amstrad CPC 464
A typical Home computer, an Amstrad CPC 464

Contents

[edit] The importance of having capable video hardware

Early home computers all had quite similar hardware, they used either the 6502 the Z80 or sometimes the 6809 microprocessor, they could have only as little as 16 KB of RAM or as much as 128K, and they could use a small 8K BASIC interpreter, or an extended 12K BASIC. So the basic systems were quite similar, except for one part of the system, the video display hardware. Some systems proved to be much more successful than others, and if you look closely you will see that the most successful systems had the most capable video hardware. The reason for that is that the success of the home computer was mostly determined by the kind of games you could play on it.

If you wanted to run a nice video game on a home computer, all the other specifications of the system, such as the CPU, the kind of BASIC, even to a degree how much memory the system had (if at least 32K or more) did not matter so much. What mattered most was what kind of picture could be put on the screen, and how easy or hard it was for a programmer to get enough capabilities out of the video hardware to create the effects necessary for his game (for example animations).

Case in point is the Commodore 64. It used the (arguably) weakest of the three above mentioned microprocessors, and its BASIC was abysmal (it was the BASIC that was developed for the Commodore PET, (a computer without any high resolution graphics capabilities at all). None of this mattered because it had the VIC-II chip. The graphic capabilities of this chip, with its ease of use, (for a machine language programmer) made it possible to develop games for it that surpassed everything that other systems of the time had. Of course, its comparatively large memory and the audio capabilities of the C64, (that were second to none at the time) were also needed to create great games, but that is material for other lists.

[edit] Video Arbitration Logic

One major problem that early computer video hardware had to overcome was the Video bus arbitration problem. The problem was to give the video hardware (VDU) continuous read access to the video RAM, while at the same time the CPU also had to access the same RAM. The obvious solution, using interleaving time slots for the VDU and RAM was hard to implement because the logic circuits, and video memory chips of the time did not had the switching speed they have now. For higher resolutions the logic and the memory chips were barely fast enough to support reading the display data, let alone for dedicating half the available time for the slow 8-bit CPU. That said, there was one system, the Apple II, that was one of the first to use a feature of the data-bus logic of the 6502 processor to implement a very early interleaving time slot mechanism to eliminate this problem.

Most other systems used a much simpler approach, and the TRS-80 simply did not have any bus arbitration at all! The CPU had access to the video memory at all times. Writing to the video RAM simply disabled the video display logic. The result was that the screen often displayed "snow", (white stripes) when there was heavy access to the video ram.

Most systems avoided the problem by having a status status register that the CPU could read, and which showed when the CPU could safely write to the video memory. That was possible because a composite video signal blanks the video output signal during the "blanking periods" of the horizontal and especially the long vertical video sync pulses. So by simply waiting for the next blanking period the snow could be avoided. This approach did have one disadvantage, it relied on the software not to write to the screen during the non-blanking periods. If the software ignored the status register the "snow" would re-appear. Another approach was to temporarily stop the CPU using the "HALT" (Z80) "WAIT" (6809) or "SYNC" (6502) control signal whenever the CPU tried to write to the screen during a non-blanking period. Other solutions were to add a hardware FIFO so that the CPU could write to the FIFO instead of directly to the RAM chip, during a blanking interval special logic circuitry then updated the video RAM with the information from the FIFO. Some later systems started using special "two port" video memory, called VRAM, that had independent data input and output pins.

[edit] The main classes of video hardware

There are two main categories of solutions for a home computer to generate a video signal.

Systems in the first category were the most flexible, and could offer a wide ranges of (sometimes unique) capabilities, but generally speaking the second category could offer a much more complex system for a comparable lower price.

Note that for completeness I have also added systems that did not really have "Video" hardware in the conventional sense, but used 7-segment displays as a visual output device.

The VDC based systems can be divided into four sub-categories.

  1. Simple video shift register based solutions, have a simple "video shifter chip", and the main CPU doing most of the complex stuff. Only one example of such a chip for a home computer exists , the RCA CDP1861 used in the COSMAC VIP. It could only create a very low resolution monochrome graphic screen. The chip in the Sinclair ZX-81 also is a video shifter, but is not a dedicated chip but a programmable chip, an ULA. The CDP1861 however was specially designed for this task only. Dedicated Video shifter chips did have some use in very early game systems, most notable the Television Interface Adapter chip in the Atari 2600. Note that although one of the chips in an Atari ST is also called a "video shift register" it does not fall into this class, mainly because the IC's in this class depend on the main CPU to feed them with picture data. They do nothing more than generate the sync signals and convert parallel data into a serial video data stream. The Atari ST's chip used a DMA system to read out video data independent of the main CPU, and contained a palette RAM, and resolution/color mode switching logic.
  2. CRTC (Cathode Ray Tube Controller) based solutions. A CRTC is a chip that generates most of the basic timing and control signals. It must be complemented with some "Video RAM" and some other logic for the "arbitration", so that the CPU and the CRTC chip can share access to this RAM. To complete the design, a CRTC chip also needs some other support logic. For example a ROM containing the bitmap font for text modes, and logic to convert the output from the system into a video signal.
  3. Video interface controllers were a step up on the ladder, these were true VLSI chips that integrated all of the logic that was in a typical CRTC based system, plus a lot more, into a single chip. The VIC-II chip is probably the best known chip of this category.
  4. Video co-processor chips are Video interface controllers that can manipulate, and/or interprete and display, the contents of their own dedicated Video RAM without intervention from the main CPU.

[edit] Explanation of the terms used in the tables

  • System Name, the name of the system, or if there are many similar versions, the name of the most well known variant, see Notes.
  • Video RAM the maximum amount of RAM used for the video display, depending on the resolution used the system may use less.
  • Text mode(s) The numbers of characters per line and lines of text the system supported. Sometimes more than one mode was possible
  • text colors The number of colors the characters could have. If more than one text mode is supported the text colors column also lists the same numbers in the same order.
  • Lower case Some systems could only display upper case characters in text mode because of their limited character set, If a system was able to also support lower case letters in a text mode, (in any highres mode it is of course always possible), then there is a "Yes" in this column.
  • Graphics modes The number of horizontal and Vertical pixels the system could display in a High resolution mode, where several high resolution modes exist each one is listed separately.
  • Graphics colors The number of colors each pixel could have in High resolution mode, If more than one high resolution mode is supported the graphics color mode also lists the same numbers in the same order.
  • Palette Support If the system could translate a "logical color" into a (larger number) or true colors using a palette mechanism then this column lists the number of logical colors the palette could accept, and the number of colors it could translate to.
  • # Sprites The total number of hardware sprites the system could support, in hardware (not counting re-use of the same hardware sprite).
  • Sprite sizes the size, in screen pixels, a Sprite could be displayed in by the hardware, as a matrix of horizontal by vertical pixels. If more than one mode could be selected they are all listed.
  • Sprite colors The total number of colors that could be used to define the sprite (transparent NOT included). If more than one sprite size mode is available each one is listed in the same order.
  • Sprites per scan-line Hardware spites use a kind of Z-buffer to determine which sprite is "on top". This limits the number of sprites that can be displayed on each scan-line. This number tells how many sprites could be displayed on a scan-line before one of them became invisible because of hardware limitations.
  • Unique features If the video display has unique features (or limitations) that could not be expressed in the table they will be listed here, as notes.

a "-" in a table cell means that the answer is irrelevant, unknown or in another way has no meaning, for example the sprite size of a system that does not support hardware sprites.

[edit] The list of homecomputers, and their video capabilities

[edit] Systems using Discrete Logic

System name Video RAM Text mode(s) lower case text colors graphics modes graphics colors palette support unique features
Acorn system 1,2,3,4,5 - 9 x 1 - - - - - 7 segment display
Apple I 729 Bytes[1] 40x24 No[2] Monochrome None - - Dumb terminal[3]
Apple II 18K[4] 40x24[5] Yes[6] Monochrome[7] 40x48,[8] 280x192[9] 16,[10] 6[11][12] None 4 line "caption"[13]
Datapoint 2200[14] 840 Bytes[15] 80x12 Yes Monochrome None - - Shift registers for RAM[16]
TRS-80 Model 1 1K[17] 32x16 64x16 No Monochrome 64x16 128x48 Monochrome No [18]
Video Genie 1K 32x16 64x16 No[19] Monochrome 64x16 128x48 Monochrome No Clone of TRS-80

[edit] Systems using simple Video Shift Registers

System name Chip Name Video RAM Text mode(s) lower case text colors graphics modes graphics colors palette support unique features
Comx-35 CDP1869 / CDP1870 3K[20] 40x24 [21] No[22] 8 240x216 (PAL)[23] 80x96 [24] 120x96 [25] 8 (4 colors per 6x4 pixels) none [26]
COSMAC VIP CDP 1861 256 Bytes ! [27] None ! - - 64x16 [28] Monochrome - Incredibly primitive

[edit] Systems using Programmable Logic

System name Chip name Video RAM Text mode(s) lower case text colors graphics modes graphics colors color resolution palette support # of sprites Sprite sizes sprites per scanline unique features
Acorn Electron ULA 20K (max)[29] 20×32 40×25 40×32 80×25 80×32[30] Yes 4_or_16, 2_or_4, 2_or_4, 2, 2 160×256, 320x256, 640x256, 320x200, 640x200 4_or_16, 2_or_4, 2, 2, 2 160×256, 320x256, 640x256, 320x200,[31] 640x200 No 0 - - None
Amstrad PCW ASIC[32] 23K 90x32[33][30] Yes Monochrome[34] 720x256 Monochrome[34] - - 0 - - Scroll RAM[35]
Sinclair Spectrum ULA 6912 Bytes 32x24[30] yes 8 (16)[36] 256x192 8 (16) 32 x 24 none none - - color limitations[37]
Timex/Sinclair TS2068 ULA 12288 Bytes (max) 32x24 yes 8 256x192, 256x192, 512x192 8,8,2 32x24, 32x192, monochrome none none - - swapping between two 256x192 screens

[edit] Systems using a CRTC

System name Chip name Video RAM Text mode(s) lower case text colors graphics modes graphics colors palette support # of sprites Sprite sizes sprites per scanline unique features
ABC 800C MC6845 16K 40x24 Yes 8 240x240 2 2 of 8 0 - - None
ABC 800M MC6845 16K 80x24 Yes 2 240x240 2 2 of 8 0 - - None
Amstrad CPC[38] MC6845 16K 20x25, 40x25, 80x25[30] Yes 16, 4, 2 160x200, 320x200, 640x200 16, 4, 2 17 of 27 0 - - None
Amstrad CPC+ MC6845 + ASIC 16K 20x25, 40x25, 80x25[30] Yes 16, 4, 2 160x200, 320x200, 640x200 16, 4, 2 32 of 4096 16[39] 16x16[40] 16 screen control[41]
Aster CT-80 MC6845 1K or 2K[42] 64x16, 32x16, 80x25, 40x25[43] yes[44] Monochrome 128x48, 160x75[45] 3 grayscales[46] none none - - Dual memory map support[47]
BBC Micro MC6845 20K (max) [48] 80x32, 40x32, 20x32, 80x25, 20x32, 40x25, 40x25 [49] Yes 2, 4, 8, 2, 2, 4, 2, 8 [50] 640x256, 320x256, 160x256, 640x200, 320x256, 160x256, 320x200, 80x75 [51] 2, 4, 8, 2, 2, 4, 2, 8 16 [52] 0 - - Teletext mode, shadow RAM support [53]
Camputers Lynx MC6845 32K[54] 40x24[30][55] Yes 8[56] 256x248 8 none 0 - - fully pixel addressable in 8 colors

[edit] Systems using a Video Interface Controller

System name Chip name Video RAM Text mode(s) lower case soft fonts text colors graphics modes graphics colors palette support # of sprites Sprite sizes sprites per scanline unique features
Acorn Risc PC VIDC20 2MB, 1MB software Yes Yes 16M Variable, eg 1600x1200x256cols[57] 16M In <=256 color modes 1 (pointer) 32x32 1 RISC OS system
Acorn Archimedes [58] VIDC1 480KB software Yes Yes 256 800x600x16cols 256 16 of 4096 1 (pointer) 32x32 1 RISC OS system
Acorn Atom MC6847 6K 32x16 No No 9 64x32[59] 68x48[60]64x64 128x64 128x64 128x96 128x96 128x192 128x192 256x192 9, 4, 4, 2, 4, 4, 2, 2, 4, 2 None 0 - - None
APF-1 MC6847 6K 32x16 No No 9 64x32[59] 68x48[60] 64x64 128x64 128x64 128x96 128x96 128x192 128x192 256x192 9, 4, 4, 2, 4, 4, 2, 2, 4, 2 None 0 - - None
Apple IIe[61] unknown[62] 19K[63] 40x24, 80x24 Yes No[64] Mono chrome 40x48, 80x48,[65] 280x192, 560×192[66] 16, 16, 6, 16[67] none none - - Split screen Graphics/Text [13]
Apple IIc[68][69] unknown[70] 19K 40x24, 80x24 Yes[71] No Mono chrome 40x48, 80x48, 280x192, 560×192 16, 16, 6, 16 none none - - Split screen Graphics/Text [13]
Apple IIGS VGC [72] 32K 40x24, 80x24 Yes No 16 40x48, 80x48, 280x192, 560×192, 320x200, 320x200, 320x200, 640x200, 640x200, 640x200, 640x200, 640x200 16, 16, 6, 16, 16, 256, 3200, 4, 16, 64, 800 Original Apple][modes none, all other modes 4096 none - - many new graphics and palette modes [73]
Dragon 32/64 [74] MC6847 6K 32x16 No No 9 64x32[59] 68x48 [60] 64x64 128x64 128x64 128x96 128x96 128x192 128x192 256x192 9, 4, 4, 2, 4, 4, 2, 2, 4, 2 None 0 - - None
Laser 200/210 and 310[75] MC6847 2K 32x16 No No 9 64x32[59] 64x64 128x64 9, 4, 4[76] None 0 - - None
Matra Alice (first model) [77] MC6847 [78] 4K 32x16 No No 9 64x32[59] 68x48[60] 64x64 128x64 128x64 128x96 128x96 9, 4, 4, 2, 4, 4, 2, 2 None 0 - - None
Matra Alice 32/90 EF9345 8K 32x16 40x25 80x25 Yes Yes [79] 8 64x32, [80] 160x125, 320x250 [81] 9,4,4 None 0 - - Video Input [82]
TRS-80 Color Computer Models 1 & 2 [83] MC6847[84] 6K [85] 32x16 No [86] No 9 64x32[59] 68x48 [60] 64x64 128x64 128x64 128x96 128x96 128x192 128x192 256x192 9, 4, 4, 2, 4, 4, 2, 2, 4, 2 None 0 - - None
TRS-80 MC-10 MC6847 4K 32x16 No No 9 64x32[59] 68x48[60] 64x64 128x64 128x64 128x96 128x96 128x192 128x192[87] 256x192 [87] 9, 4, 4, 2, 4, 4, 2, 2, 4, 2 None 0 - - None

[edit] Systems using a Video Co-Processor

System name Chip name Video RAM Text mode(s) lower case soft fonts text colors graphics modes graphics colors palette support # of sprites Sprite sizes sprites per scanline unique features
Atari 8-bit family [88] ANTIC plus CTIA/GTIA 15K of 64K [89] 40x24, 20x24, 20x12 Yes [90] Yes [91] 1,1,1 40x24, 80x48, 160x96, 160x192, 320x192, 80x192 4, 2 or 4, 2 or 4, 2 or 4, 2, 9 [92] Yes[93] 4 8x256(max) 4 Many, especially the display list
Coleco Adam TMS9918A[94] 16K 32x24[95] Yes Yes 2,16 64x48, 256x192, 256x160[96] 16,16,16 none 32 8x8, 16x16 4 [97] color limitations
Commodore VIC-20 VIC [98] 1½K[99] 22x23[100] Yes[101] Yes 2[102] 176x184[103] 4[104] No[105] 0 - - Some[106]
Commodore 64 VIC-II 16K 40x25 Yes Yes 16 320x200, 160x200 16 No 8 24x21, 12x21 8 Some
Commodore Amiga (first generation)[107] AGNUS[108] and DENISE[109] 1M (MiB) "chipram"[110] Any textsize up to 80x32[30] Yes Yes 2 to 32, 64[111] 320x200, 640x200 (and 320x400, 640x400 interlaced)[112] 2 to 32, 64[111] and 4096[113] 2 to 32 colors out of 4096 colors 8[114] 16 wide, arbitrary height[115] 8 Many unique features[116]
Commodore Amiga (second generation)[117] Super-AGNUS[118] and Super-DENISE[119] 2M "chipram" Any textsize up to 160x32 Yes Yes 2 to 32, 64, (4 in superhighres)[120] 320x200, 640x200, 320x400, 640x400,[121] 1280x200, 1280x256 2 to 32, 64 and 4096 2 to 32 colors out of 4096 colors 8 16 wide, arbitrary height 8 even more unique features[122]
Commodore Amiga (Third generation)[123] Advanced Graphics Architecture (AGA)[124] 2M "chipram" Any textsize up to 160x32 Yes Yes 2 to 256 (16 in superhighres). NTSC: 320x200 .. 1280x400. PAL: 320x256 .. 1280x512. VGA: 640x480. Super72: 400x300 .. 800x600. 2 to 256. 4096 and 262,144[125] 2 to 256 colors out of 16,777,216 colors 8 64 wide, arbitrary height 8 still more unique features[126]
Memotech MTX500[127] TMS9918A[94] 16K 32x24 40x24 Yes Yes 2,16 64x48, 256x192 16,16 none 32 8x8, 16x16 4 [97] color limitations
SV-318 TMS9918A[94] 16K 32x24 40x24 Yes Yes 2,16 64x48, 256x192 16,16 none 32 8x8, 16x16 4 [97] color limitations
SV-328 TMS9918A[94] 16K 32x24 40x24 Yes Yes 2,16 64x48, 256x192 16,16 none 32 8x8, 16x16 4 [97] color limitations
Tatung Einstein TMS9918A[94] 16K 32x24 40x24 Yes Yes 2,16 64x48, 256x192 16,16 none 32 8x8, 16x16 4 [97] color limitations
TI-99/4 TMS9918[128] 16K 32x24[129] No Yes 2,16 64x48[130] 16,16[131] none 32 8x8, 16x16 4 [97] color limitations
TI-99/4A TMS9918A[94] 16K 32x24[129] No[132] Yes 2,16 64x48, 256x192 16,16[131] none 32 8x8, 16x16 4 [97] color limitations

[edit] Systems that could not be classified

If you know more about the actual hardware used by these systems, then please move them to the correct class.

System name Chip name Video RAM Text mode(s) lower case text colors graphics modes graphics colors palette support # of sprites Sprite sizes sprites per scanline unique features
Panasonic JR-200 unknown unknown[133] 32x24 Yes 8 192x256[134] 64x48 8 unknown None - - Serial attributes[135]

[edit] Notes

  1. ^ actually the real figure is more complex, its 6144 bits of which 5760 bits were actually used. This is so because the video data was stored, not in RAM, but in six Signetics 2504 "Dynamic shift registers" which each held 1024 bits. But only 40x24=960 locations in the shift register were actually used.
  2. ^ the six bits per character location were only enough to address 64 characters, A Signetics 2513 character generator ROM held only uppercase characters and some other alphanumerical characters in a 5 x 7 matrix.
  3. ^ The video display generator of the Apple 1 was NOT memory mapped but acted as a (very) Dumb terminal. Data was sent to the terminal through an 7 bit parallel port, and a strobe. Six bits were used to choose which character was displayed next, after the last one on the screen at the "cursor position". The six bits corresponded directly with the character selection bits of the Signetics 2513 character generator ROM. When the seventh (most significant) bit was high, it meant the six least significant bits had to be interpreted as a "command", but only two commands existed. The "carriage return" command made it so that the next character would appear at the start of the next line, and the "clear screen" command which would fill all the video memory with spaces, and resetted the cursor position to the top left corner. A "busy" bit could be read from the terminal to determine it was ready to accept a new character. Interestingly the counters that were used to create the video timing were also used to create the RAM refresh signal for the 4K main memory. In many ways, the APPLE I's VDU resembles the one of the Datapoint 2200.
  4. ^ The Apple 2 has a 1K text buffer for the 40x24 text mode or the 40x48 low resolution graphics mode, and a 8K frame buffer for the 280x192 High resolution graphics mode. But because the apple had two text and two graphics pages the total reserved memory for video is 18K. The first text/low-resolution page runs from 0400H to 07FFH, the second from 0800H to 0BFFH. The first high-resolution frame buffer runs from 2000H to 3FFFH and the second one from 4000H to 5FFFH.
  5. ^ in a 5x7 dot matrix with one pixel on either side of characters and a one dot high space between each line.
  6. ^ Characters could also be inverted or blinking, The arrangement was not completely ASCII compatible! Characters from 00H to 3FH were inverted, from 40H to 7FH were flashing, from 80H to 9FH uppercase characters only, from A0H to DF the normal complete set, and from E0H to FFH the lowercase characters only, so all 256 combinations were used
  7. ^ The apple turns the colorburst circuitry during text modes off to give a clearer text
  8. ^ using text mode, where instead of characters a stack of two pixels were displayed
  9. ^ The apple only displayed 7 pixels of each byte of the frame buffer, the eight one was used to determine which color combinations the pixels of the other seven bits could have
  10. ^ each byte of text mode ram was divided in two nibbles. The "lower" nibble determined the color of the top block, the upper nibble determined the color of the lower blok. The sixteen available colors were: black, magenta, dark blue, purple, dark green, grey 1, medium blue, light blue, brown, orange, grey 2, pink, light green, yellow, aquamarine, white
  11. ^ There are six colors available in the High-Resolution Graphics mode: black, white, red, blue, green and violet. Each dot can be either black, white or a color, although not all colors are available for every dot. If a pixel would be 0 then the corresponding pixel would become black, if it was 1 It would become either white, or a color. Which color a pixel in a 7 pixel "line" of dots would become was determined both by the eight bit of the pixel data byte, but also by its bit location in the byte. If the bit was in the leftmost column on the screen, or in any even-numbered column, then it would appear violet. If the bit was in the rightmost pixel column, or any odd numbered column, it would become green, except when two even and odd pixels were on belongside each other, then both pixels would be white. All this is true for all seven pixels of a display byte where its eight bit would be 0 (off), if this bit was turned "on" (to 1), then the violet and green would be exchanged by blue and red.
  12. ^ except in revision 0 board, which could only display 4 colors, black, white, green and violet, because the eight bit of the display byte had no effect
  13. ^ a b c In high or low resolution graphics mode the apple could replace the bottom 32 display lines with a four line text "caption", so you could simultaneously display text and graphics.
  14. ^ The Datapoint 2200 is considered to be the first personal computer, and its CPU resembles Intel's first 8-bit processor, the 8008. This is the case because Intel copied the Datapoints CPU architecture! From the 8008 came the 8080, and from the 8080 and 8085 8-bit CPU, The 8086 was the 16-bit version, and from that the Pentium and all current CPUs used in PCs and Mac's. This not only makes the Datapoint the first PC, but also the granddaddy of all current PC's!
  15. ^ Actually its 960 characters (12x80) of seven bit. There were 95 different characters in the 5x7 matrix character ROM, and the datapoint used 7-bits per character to address them
  16. ^ The Datapoint used shift registers for its video RAM, and used the power line frequency timing (50 or 60 cycles per second) for a complete refresh cycle. When writing to the Display the CPU had to wait for the next "window", which came 50 (or 60) times a second. Then the CPU could write a single character, or (with special software) multiple characters, up to all 960.
  17. ^ Actually its less than 1K, its 7168 bits, because there were only seven 1024x1 bit RAM's used to store the seven bits per character. That is also why lowercase could not easily be accomplished. Of the 128 possible characters 64 were used for the "pseudographics", and the remaining 64 came from a character generator PROM that only contained uppercase characters
  18. ^ each character mapped to a matrix of 2x3 pixels to generate a semi-high resolution mode". No video ram arbitration logic meant that writing to the screen cause a lot of "snow".
  19. ^ The later Genie 1 added lowercase support
  20. ^ 1K (960 Bytes Video ram and 2K character RAM for 128 programmable characters (8x8 Bytes NTSC or 8x9 Bytes PAL, RAM was available for 8x16 which was possible to use via assembler code)
  21. ^ In Assembler the witdh and/or height of the characters could be doubled, so 20x24, 40x12 and 20x12 was also possible
  22. ^ Except by reprogramming the characterset, But BASIC used uppercase only
  23. ^ Using a programmable font (with 128 characters 6 pixels wide and 9 pixels high) that meant that not each pixel of the theoretical 240x192 could be individually addressed. In fact at most 128x6x9 = 6912 individual pixels could be addressed at any one time
  24. ^ One way to create a real highres mode was to program the characterset by diving the 6x8 pixels of the character into 2x4 zones (like the TRS-80 graphics mode which used 2x3 zones), in this way a 80x96 point addressable highres mode was feasible
  25. ^ By using the max character size of 6x16, double height and double witdh a resolution of 120x96 was possible.
  26. ^ The Comx-35 has a strange setup with minimal video ram, just 960 bytes character data and 2K RAM for 128 programmable characters. No highres modes Each character was 6x8 pixels, leaving two pixels (bits) that were used to select one of four (foreground) colors per halve character
  27. ^ expandable to 2K
  28. ^ 64x16 when using ¼K of RAM 64x32 when using ½K of ram 64x64 with 1K of ram
  29. ^ Depending on the screen mode used
  30. ^ a b c d e f g All text output produced by software in Highres graphics modes
  31. ^ spaced display with two blank horizontal lines following every 8 pixel lines
  32. ^ It's unclear if the PCW's ASIC was a completely dedicated chip designed from scratch or a gate array
  33. ^ because the margins were normally not used the actual line only had 80 characters
  34. ^ a b Black and green
  35. ^ with a resolution of 720 by 256. Even with one bit per pixel, the PCW's video buffer occupied 23 K of RAM, making software scrolling far too slow for fluid text manipulation. In order to improve this, the PCW implemented roller RAM, with a 512-byte area of RAM used to hold the address of each line of display data, effectively allowing very rapid scrolling. The video system also fetched data in a special order designed so that plotting a character eight scan lines high would touch eight contiguous addresses. This meant that very fast Z80 copy instructions like LDIR could be used. Unfortunately, it meant that drawing lines and other shapes could be very complicated.
  36. ^ Eight colors, but with two brightness levels, so actually with 16 color tints
  37. ^ The Sinclair Spectrum high resolution screen has serious color limitations. Each 8x8 pixel block can have only one set of foreground and background colors. This is because of the separate 960 byte color table, (one byte for each 8x8 pixel block). In each of these bytes the lower three bits (0-2) are the background color, the next three higher bits (3-5) are the foreground color and the two remaining high order bits were used for a "bright" (6th) and a "blinking" (7th) bit, so you could say the sinclair had 16 colors, eight with low brightness, and eight with high brightness. Of course the color limitations of this design can cause some heavy attribute clashes, for which the Spectrum is indeed infamous. For more information see ZX Spectrum graphic modes.
  38. ^ Pertaining to the Amstrad CPC 464, 472, 664 and 6128
  39. ^ with an independent palette of 15 colors, but sprite pixels can also be transparent, and each logical color can be any of 4096 colors
  40. ^ three levels of magnification, 1x, 2x and 4x. Independent for X and Y axis
  41. ^ Additional screen controls have been added to allow split screen operation and facilitate smooth scrolling.
  42. ^ Depending on the boot floppy used, the Aster reconfigured its internal memory map for use as a TRS-80 compatible machine or a fully CP/M compatible machine, including the location in the internal memory map of the video memory. In TRS-80 mode it used 1K (16 lines of 64 characters) and used all 8 -bits of the character to support a full set of 256 characters, and in CP/M compatible mode it used 2000 bytes (25 lines of 80 characters) of a dedicated 2K memory, using the same character-set as the TRS-80 mode
  43. ^ in TRS-80 as well as in CP/M mode the Aster could switch to a display mode where it would only display the odd display memory bytes at double width. The 40x25 mode was initiated when the system was booted with a special Videotex terminal emulator program. In both modes a hardware "de-snowing" (Video memory arbitration system) system was employed that removed the bothersome "snow" that appeared on a TRS-80 screen whenever the system made a large amount of accesses to the video memory. The memory arbitration logic did not need software support, so it also worked with all existing software
  44. ^ although the original TRS-80 model 1 did not support lowercase the Aster did. It also supported a second copy of the 2x3 semi graphics set that was dithered to emulate a "grey" version of the TRS-80 graphics pixels, and it supported a set of semi-graphics characters similar to the PETSCII set
  45. ^ 160x75 only in the CP/M compatible mode
  46. ^ Actually, the Aster could display the TRS-80 graphics in black (pixel off), white (pixel on) and one grayscale halfway in-between black and white, which was accomplished by dithering the pixels in the semi-graphics block with a checkerboard pattern
  47. ^ The Aster system could switch "on the fly" between two completely different system architectures, and also switched its video logic and memory map accordingly, it also lowered the dot clock (crystal) in CP/M mode, so the 64X16 and 80x25 screens were equally wide
  48. ^ The teletext mode only used 1K of memory, the others from 8 to 20K as needed
  49. ^ Using Teletext mode with the aid of an SAA5050 mode, in this mode the Beeb only needed 1K RAM
  50. ^ by using serial attributes, as common in Teletext systems
  51. ^ using the 2x3 block graphics of teletext mode
  52. ^ Modes 0 to 6 could display a choice of colors from a logical palette of sixteen, though only eight colors were available; the eight basic RGB colors (0-black, 1-red, 2-green, 3-yellow, 4-blue, 5-magenta, 6-cyan, 7-white) and eight colors in a flashing state, (8-black/white, 9-red/cyan, 10-green/magenta, 11-yellow/blue, 12-blue/yellow, 13-magenta/green, 14-cyan/red, 15-white/black)
  53. ^ Mode 7 was a Teletext mode and extremely economical on memory, using only 1K, In addition, the BBC B+ and the later Master allowed 'shadow modes', where the framebuffer was stored in 20 K of extra RAM mapped to location 0x8000 onwards ('shadowing' the BASIC ROM mapped to that area), instead of taking up the user memory below 0x8000. This feature was enabled by setting bit 7 of the mode variable, i.e. by requesting modes 128–135.
  54. ^ Or less when one or more "display pages" were turned off. The lynx used a display page for each of the three primary colors. For example when the BASIC instruction TEXT was executed the lynx turned off the display panes for red and blue, so it could reclaim ⅔th of the memory for the display for bigger programs (with all planes on the Lynx had just 16K left for programs) and this also increased the speed of the system because the VDU did not prohibit the CPU access to the memory so often
  55. ^ The lynx used a trick, the natural resolution of 256 pixels would have called for a display of only 32x24, but by only using 6 pixels wide characters the Lynx could fit in 40 per line, only a very large software overhead was needed, so the display was slow, so slow in fact that the software did not scroll a text screen but simply started on the top line again
  56. ^ Black, blue, red, magenta. green, cyan, yellow and white
  57. ^ No fixed graphics modes, any mode can be generated by supplying timings. Modes are limited only by analogue video bandwidth, video RAM or DRAM bandwidth and minimum refresh rate monitor will accept. Definitions for common monitors are supplied up to 1600x1200x256cols.
  58. ^ All Acorn A-series machines (A300, A5000, etc) except A7000(+)
  59. ^ a b c d e f g The characterset includes 8 (one set for each color) x16 characters with a 2x2 pixel matrix, with this a mixed text and semi graphics mode can be created that can display pixels in 8 colors against a black background, albeit with some color clash
  60. ^ a b c d e f Another semigraphics mode, like the 32x64 mode, but exchanging a more limited number of color for a somewhat higher resolution
  61. ^ The apple IIe used a dedicated chip to replace most of the discrete logic of the apple II, all comments for the apple II apply to the apple IIe, but the apple IIe has additional possibilities
  62. ^ It is not known whether the special chip for the apple IIe had a name
  63. ^ The Apple IIe had an extra 1K of video ram for the 80 columns text mode.
  64. ^ The apple used a hardware character generator, But could not mix text and graphics except by displaying four lines of text beneath the graphics screen, also the text was strictly black and white, so often text on the screen was displayed using software so colored text could be displayed in different fonts
  65. ^ double low resolution mode, using the extra 1K text mode
  66. ^ using the "resolution doubler" originally developed for the double low resolution mode, uses the second bank of high resolution RAM.
  67. ^ effectively the color resolution was only 140×192, due to pixel placement restriction
  68. ^ And Apple IIc Plus, which has identical graphics capabilities
  69. ^ has all the capabilities of the Apple IIe, and an improved character set
  70. ^ It is not known whether the special chip for the apple IIc had a name
  71. ^ The apple IIc now used a small part of the characterset to display special "mouse graphics" symbols, and the character ROM was doubled in size, so it was possible to switch to a characterset that could display extra local language characters and symbols such as accented letters such as "á", "é", "ç" etc.
  72. ^ Video Graphics Chip
  73. ^ * 320×200 pixels with a single palette of 16 colors.
    • 320×200 pixels with up to 16 palettes of 16 colors. In this mode, the VGC holds 16 separate palettes of 16 colors in its own memory. Each of the 200 scan lines can be assigned any one of these palettes allowing for up to 256 colors on the screen at once. This mode is handled entirely by the VGC with no CPU assistance, making it perfect for games and high-speed animation.
    • 320×200 pixels with up to 200 palettes of 16 colors. In this mode, the CPU assists the VGC in swapping palettes in and out of the video memory so that each scan line can have its own palette of 16 colors allowing for up to 3200 colors on the screen at once. This mode is computationally-intensive however, and is only suitable for viewing graphics or in paint programs.
    • 320×200 pixels with 15 colors per palette, plus a "fill mode" color. In this mode, color 0 in the palette is replaced by the last non-zero color pixel displayed on the scan line (to the left), allowing fast solid-fill graphics (drawn with only the outlines).
    • 640×200 pixels with four pure colors. This mode is generally only used for ensuring that the Apple logo and menu bar retain their colors in Desktop applications.
    • 640×200 pixels with 16 dithered colors. In this mode, two palettes of four pure colors each are used in alternating columns. The hardware then dithers the colors of adjacent pixels to create 16 total colors on the screen. This mode is generally used for programs requiring finer detail such as word processors and the Finder.
  74. ^ The dragon was virtually identical with the TRS-80 Color Computer except it had at least 32K RAM and used additional circuitry to generate a PAL signal instead of NTSC
  75. ^ The VTech Laser 200 was also called the "Salora Fellow" (mainly in Scandinavia, particularly Finland), the "Texet TX8000" (in the United Kingdom) and the Dick Smith "VZ 200" (in Australia and New Zealand)
  76. ^ On a 2x2 pixels basis, with two choices of background colors
  77. ^ The First model of the Matra Alice was an exact copy of a Tandy Model MC-10 with 4K ram
  78. ^ The original model, the later Matra Alice 32 and Matra Alice 90 had another video chip, the EF9345
  79. ^ 3x100 user definable characters, but only in 40x25 text mode
  80. ^ Using 2x3 pseudo graphic characters
  81. ^ These resolutions could be achieved by "faking" them using the programmable characters
  82. ^ The Matra Alice 90 featured video-in, so EF9345 graphics could be overlaid onto the input video
  83. ^ There were three models, but the video display capabilities of the first two models differed only slightly
  84. ^ Some later models of the CoCo models 2 used the MC6847T1.
  85. ^ except for early 4K models of the CoCo, consequently the video modes that needed more memory were not supported
  86. ^ Later models that used the MC6847T1. did support lower case
  87. ^ a b With 20K memory expansion pack only
  88. ^ Including the Atari 400, 800 XE and XL
  89. ^ The extreme flexibility of the ANTIC chip meant that it in theory could use the whole 64K of addressable memory space, but the highest of all possible resolutions could only display 15K of the memory
  90. ^ "Lowercase with descenders" mode, which was not available through GRAPHICS, only as part of custom display lists. In this mode characters were 10 pixels high and occupied either the upper or lower 8 pixels of that height. This was not strictly speaking a 40×24 text mode, because of the unusual height.
  91. ^ The character set was easily redirected by changing an ANTIC register, allowing the user to create their own character sets with relative ease.
  92. ^ 9 colors from the color palette registers or All 15 Atari hues, but only of one brightness (plus black) or All 16 Atari shades, but only of one hue
  93. ^ the ability to invert all the text on the screen by changing a value in memory
  94. ^ a b c d e f the "Texas Instruments TMS9918" is actually a familiy of devices. The TMS9918A outputs 60 Hz NTSC composite video and TMS9928 and TMS9929 output three separate signals (Y, R-Y and B-Y) with which either a 60Hz NTSC (TMS9928A) or a 50Hz PAL or SECAM (TMS9929A) video signal could be created
  95. ^ A 40 x 24 text mode is theoretically possible but is not supported in Coleco BASIC
  96. ^ Coleco Adam BASIC created a mode with a 256x160 pixel graphics "window" on top, and used the remaining 256x32 pixel window to create four lines of 32 characters of text
  97. ^ a b c d e f g TMS9918/28 based systems: in 32x24 text mode the characterset is divided in 32 blocks of eight character. each block of eight characters can have a different foreground and background color. This can be used in games, because it is possible to generate a relatively fast high resolution mode by reprogramming the characters as 8x8 tiles and grouping them together in blocks of eight with the same colors. The tiles can then be manipulated quickly through the character pointer table. Sprites could be used too in this mode, and all 16 colors could be displayed at the same time. Another use is to have four identical character-sets with each 64 characters in them but with different colors. with this character set it is possible to create a 32x24 text mode that can display texts with four different foreground and background colors at the same time, on the same screen. In 256x192 graphics mode there is a 2-color limitation for each 8 pixel wide line inside a character, so this can cause some attribute clash although not as severe as on the ZX Spectrum.
  98. ^ or 'Video interface controller', Pertaining to the MOS technology 6560 (NTSC version) and the 6561 (PAL version) chips. These chips did more than supporting the video display, they also provided the sound system, and had two A/D converters for its paddle game control system
  99. ^ The Vic could address 16K of address space for screen, character and color memory. But only 5K points to RAM on the VIC-20 without a hardware modification, and the VIC only had a grand total of 5K of which only 1½K was reserved for the screen
  100. ^ 8x8 characters, the VIC also supported 8x16 characters
  101. ^ Like on the PET, 256 different characters could be displayed at a time, normally taken from one of the two character generators in ROM (one for upper-case letters and simple graphics, the other for mixed-case -- non-English characters were not provided)
  102. ^ 2, because in the usual display mode, each character position could have its foreground color chosen individually, and the background and screen border colors were set globally. A character could be made to appear in another mode where each pixel was chosen from 4 different colors: the character's foreground color, the screen background, the screen border and an "auxiliary" color; but this mode was rarely used since it made the already wide pixels pixels twice as wide as they normally were.
  103. ^ 176 × 184 is the standard for the VIC-20 firmware, although at least 224 × 256 is possible on a PAL machine. The VIC chip did not provide for a direct full-screen, high-resolution graphics mode. It did, however, allow the pixel-by-pixel depictions of the on-screen characters to be redefined (by using a character generator in RAM), and it allowed for double-height characters (8 pixels wide, 16 pixels high). It was possible to get a fully-addressable screen, slightly smaller (160 by 160) than normal, by filling the screen with a sequence of 200 different double-height characters, then turning on the pixels selectively inside the RAM-based character definitions. (The 200-character limitation was so that enough bytes would be left over for the screen character grid itself to remain addressable by the VIC chip.) The Super Expander cartridge provided such a mode in BASIC, although it often had to move the BASIC program around in memory to do it. It was also possible to fill a larger area of the screen with addressable graphics using a more dynamic allocation scheme, if the contents were sparse or repetitive enough.
  104. ^ For Highres graphics modes the double wide text mode was used, which proved for four different colors per pixel in each 8x16 character tile. For each tile the colors could be chosen out of a palette of 16 colors, but the upper 8 could only be used in the global background and auxiliary colors
  105. ^ not really, but something similar could be done by manipulating the four colors out of sixteen possible color chosen for each tile, or the global background color
  106. ^ The VIC-20 had hardware support for a Light pen, but its most obvious feature was its text mode with very wide characters
  107. ^ Pertaining to the Amiga 1000, Amiga 2000 and Amiga 500 machines
  108. ^ For DMA memory access and Blitter functions, and a Copper (co-processor), a programmable finite state machine that executes a programmed instruction stream, synchronized with the video hardware
  109. ^ the main video processor. Without using overscan, the display was 320 (lowres) or 640 (hires) pixels wide by 200 (NTSC) or 256 (PAL) tall. It also supported interlacing which doubled the vertical resolution. Anything between 2 and 32 unique colors (1 to 5 bitplanes) from a 12 bit (4096 color) palette, was supported. A 6th bitplane was available for either the Halfbrite mode that added a copy of the first 32 colors but with half the intensity or Hold And Modify mode which allowed access to all 4096 colors at once. Denise supported eight sprites, smooth scrolling, and "dual playfield". For more information see Original Amiga chipset.
  110. ^ Older versions could only access 512K chipram
  111. ^ a b in "halfbright mode". Extra Half-Brite (EHB) mode uses 6 bitplanes (6 bits/pixel), where the first 5 bitplanes index a color from the color palette (consisting of 32 colors). If the bit on the 6th plane is set the color brightness is halved for each color component. This way 64 simultaneous colors are possible while only using 32 color palette registers.
  112. ^ 320x256, 640x256, 320x512 and 640x512 in PAL mode
  113. ^ Using "hold and modify" (HAM-6) mode, a mode specially designed for displaying photos, see Hold-and-Modify
  114. ^ The Amiga's hardware engine supports only 8 sprites, but with copper support, can present the illusion of many more. Each sprite is drawn in a certain position, until the raster beam has passed it; the copper can then instantly change its location and appearance, moving it below the raster beam again
  115. ^ 3 colors (plus a fourth transparent "color"). Two sprites could be attached to make a single 15-color sprite.
  116. ^ Too many to mention, see Original Amiga chipset
  117. ^ Pertaining to the Amiga 3000 machines
  118. ^ For DMA memory access and Blitter functions, and a Copper (co-processor), a programmable finite state machine that executes a programmed instruction stream, synchronized with the video hardware
  119. ^ Could do all the things the original AGNES chip could and added support for Productivity (640×480 noninterlaced) and SuperHires (1280×200 or 1280×256) display modes, which were however limited to only 4 colors. Also the blitter could copy regions larger than 1024×1024 pixels in one operation. Sprites could be displayed in border regions (outside of any display window where bitplanes are shown).
  120. ^ Four colors only in the new "super resolution" modes
  121. ^ Now In non interlaced too
  122. ^ Even more features than the original chipset, see Original Amiga chipset
  123. ^ used in the CD32, Amiga 1200 and Amiga 4000.
  124. ^ AGA is able to do 8-bit pixels, which gives 256 colors in normal display mode and 262144 colors in HAM-8 (Hold-And-Modify) mode (18-bit color, 6 bits per RGB channel). Palette for AGA chipset is 256 entries from 16,777,216 colors (24-bit). The original Amiga chipset (OCS) had 4096 colors (12-bit, 4 bits per RGB channel), of which 32 could be displayed unless in half-bright (which provided an additional 32 colors fixed at half the brightness of the first 32) or HAM mode.
  125. ^ Using "hold and modify" (HAM-8) mode, a new super high color mode Hold-and-Modify
  126. ^ Other features added to AGA over ECS were superhires smooth scrolling and 32-bit fast page memory fetches to supply the graphics data bandwidth for 8 bitplane graphics modes and wider sprites see Advanced Graphics Architecture, the CD32 has an Akiko bitmap to planar conversion chip
  127. ^ The Memotech MTX512A and RS128 machines have the same video capabilities as the MTX500
  128. ^ The TI99/4 was the only system to use the old TMS9918, instead of the TMS9918A. This VDP did not support mode II graphics
  129. ^ a b A 40 x 24 mode was theoretically possible with assembler, but was not supported in TI-BASIC
  130. ^ The TI-99/4 used a TMS9918 (not TMS9918A), and this older chip did not support 256x192 (mode II) Graphics
  131. ^ a b Actually 15 colors, the 16th color was "transparent" and was designed to display a background video signal from a genlock
  132. ^ No lower case support, but the TI-99/4A Did support "small characters" instead of lowercase
  133. ^ The text buffer is 768 Bytes, but it is not known what the size of the color attribute ram is
  134. ^ Not point addressable, but through a programmable character set
  135. ^ It seems this system uses a serial attributes scheme, similar to the Oric Atmos but no details are known, perhaps it's just a feature of its BASIC.

[edit] See also

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