deng@shire.cs.psu.edu (03/07/89)
Weeks ago, I posted a question about VGA, EGA and CGA. Thanks for those who responsed. I think other netters can also benefit from these notes. Here is the summery of the responses I got. -------------------------------- Those three are (color graphics) video display standards. In each case, the term originally applied only to IBM hardware ... Unfortunately, IBM did not supply adequate BIOS support even for TEXT mode operation, so that software developers were forced to write software that manipulated the hardware directly, so that hardware compatibility is a significant issue. IBM compatible display adapters STILL do not supply any BIOS support for graphics operations, making it very difficult to add new gee-whiz graphics hardware to IBM systems. CGA is the oldest standard. It supports 80x25(x16 colors) and 40x25(x16) text modes, and 640x200x2, 320x200x4 graphics modes. The limit in the graphics modes is caused by a 16K display buffer limit. The original IBM CGA had a glitch: if you updated the display except during horizontal or vertical retrace periods, you got "snow" on the screen. CGA uses a RGBi monitor (i.e. 4 signals: red,green,blue,intensity, yeilding 16 combinations). EGA is the middle standard. While EGA can emulate the CGA modes, the control registers are not exactly the same. CGA-based Programs which use the BIOS to set up the various operational modes, and then use either BIOS or direct hardware writes to update the display will function properly with an EGA. EGA provides additional modes of 80x43x16 text, 640x350x16 graphics. EGA also has a "pallete" of 64 colors, of which 16 at a time can be displayed. EGA uses a RGBrgb monitor (i.e. 6 signals: low intensity and high intensity red,green and blue, yielding 64 combinations). VGA is the latest standard. These originally were available only on PS/2 machines, but clone makers have outdone IBM again. VGA is almost-compatible with EGA: most of the control registers are identical: only a few unused bits now have meanings. A few random differences: VGA does not support a light-pen, and does not have retrace interrupt support. VGA adds a 80x50x16 text mode and 640x480x16 and 320x200x256 graphics modes. VGA adds a true color pallette: Each "color" in the EGA pallette can now represent any one of 262164 possible colors by converting 64 bits each of red,green,blue data into an analog color. VGA uses an ANALOG monitor, which means that it theoretically can display an infinite variety of colors. > and what 'campatible to VGA and EGA' implies? As with any other claim of compatibility, they mean whatever you want them to mean. Because of the lack of BIOS support, all IBM display adapters MUST be compatible at some level to be able to operate. There are usually 2 levels of compatibility: 1. BIOS compatible, which implies that if you set display modes via the BIOS, then you can successfully write to the hardware directly to update the display: (i.e. EGA and VGA display boards are BIOS compatible with the CGA). The other level of compatibility is REGISTER compatibility: This means that ALL the hardware control registers are compatible with the IBM version of the display adapter, and any software which manipulates these registers directly will function properly. john nelson UUCP: {decvax,mit-eddie}!genrad!teddy!jpn smail: jpn@teddy.genrad.com ------------------------------ .......... I'm not directly familiar with VGA, but I've never seen anything in the config.sys file having to do with display unless you use the ANSI.SYS driver. .... I'm pretty sur video cards are self-configuring. ......... The model 30 uses a hybrid display mode called MCGA. It's only available on the Model 30 and 25 with 8086 processors. It's a modified version of CGA and hasn't really been supported by developers. They see it as something that's not really worth supporting because VGA is a much better display standard and there aren't as many MCGA displays as EGA or VGA. Unfortunately, that's all there is to it. I'm pretty sure that you can bump your display back down to CGA mode and should be able to use just about everything you want in that mode. Of course, the display won't be as good... -Ace swerling@caen.engin.umich.edu (Ace Swerling) ------------------------------ CGA (Color Graphics Array) is 320x200 with 4 colors out of a palette of 16 EGA (Enhanced GA) is 320x200 with 16 colors out of 256. MCGA (Multi-color GA) is 320x200 with 256 out of 256,000 or 640x480 with only 2 colors VGA (Video GA) is 320x200 with 256 colors out of 256,000 or 640x480 with 16 colors out of 256 colors Some VGA have 800x600 with only 2 colors. Being compatible with these grpahics systems means that the program will send the appropriate signals to turn on the right pixels. Some VGA adapters, however, are not downward compatible or register-compantible and therefore will not run CGA, EGA, etc. A good one to get is Quadram Quad 4 Plus. Jason Gross Comp Sci Ugrad University of Miami Class of '91 (?) =========================================================================== "Not my goddamn | At the tone, leave your reply and Visa card number at: planet, monkey- | Internet: gtww2z9z@umiami.miami.edu boy." - B. Banzai | Bitnet: The man said "Soon!" =========================================================================== ** Disclaimer: Disclaimer? Why, I never claimed 'er in the first place! ** CGA, EGA and VGA all stand for IBM's video interface standards, and each corresponds to an adapter card that IBM provided with various systems. The main difference between them is in resolution of the image and the number of colors available. CGA (Color Graphics Adapter) was first available with early PC systems, and provides 16 colors and 640 lines X 200 lines of resolution. Most graphics- and color-oriented software written until recent years was written for this standard. Its character rendition is generally considered to be poor for text-intensive applications. EGA (Enhanced Graphics Adapter) has gained popularity more recently, due to its superior character rendition in either 25- or 43-line modes, and greater graphics resolution (up to 640 X 350). EGA can also display 16 simultaneous colors, but these 16 are drawn from a palette of 64. EGA requires a monitor capable of handling the higher resolution is required for an EGA adapter card. EGA cards are generally fully CGA-compatible. Most business software and other recent software (including MicroSoft Windows) requires EGA. VGA is the latest and greatest. It was introduced by IBM with its PS/2 line. It supports up to 640 X 480 resolution, and 16 colors frmo a palette of 256,000 (!) colors. Actually, one VGA mode supports lower resolution (320 X 200) with 256 simultaneous colors. The popular MultiSync or MultiScanning monitors you may have seen around are able to handle higher-than-EGA resolutions, and in some cases, VGA. Because of the higher clock rates and bandwidth required for VGA, VGA-compatible monitors use analog display technology instead of the TTL (digital) technology used before. The MultiSync monitors have two input connectors and can handle the two different output modes, depending on the adapter card to which they're connected. It sounds like you're shopping either for a card or a monitor, so I suggest you take peek at BYTE February and March '88. = Marc Johnson BITNET: rna!marc@rockvax.bitnet = = Rockefeller Univ. Neurobiology UUCP: ...cmcl2!rna!marc = = New York City INTERNET: marc%rna@rocky2.rockefeller.edu = = (129.85.2.1) = ------------------------------ CGA = Colour graphics adapter. Likje a monochrome display adapter with 160x100 16 colour, 320x200 4 colour and 640x200 monochrome graphics. Colour registers exist on CGA and EGA with 6 bits for each colour which define the physical colour displayed for a given colour number. EGA = Enhanced graphics adapter Can emulate a CGA to an extent - some clone boards emulate CGA properly - as well as a 640x350 monochrome, 640x350 16 colour. Text is much easier to read on EGA than CGA VGA = Video Graphics Adapter Can emulate EGA and CGA - most can do so fully. Some also emulate MDA and Hercules. Ideally you should try to get one which has full register level downward compatibility with CGA and EGA. Text modes are enhances by adding an extra 50 scan lines (350->400), and there are 3 new graphics modes - 640x480 2 colour, 640x480 16 colour and 320x200 256colour. There are 64 ... oops 256 colour registers each with 24 bits, although only 18 bits are used, with 256000 possible colours and shades. Most modes can take advantage of this. Some cards have additinal modes including: 132x44 text, 132x25 and 132x28 all with 4 colours 1056x352, 1056x350, 1056x364 all 16 colours 640x40 800x600 256 colours 024x768 16 colours Internet: avenger@runx.ips.oz.au ________________________ UUCP: uunet!runx.ips.oz.au!avenger /\ \ \_| | Watch out for gobbledocks - | Core Publications | They'll steal all your silicon Chippies | Electronic Publishing | | ____________________|_ \_/_____________________/ ------------------------------ ...... There are also enhanced ega cards with higher resolutions, i.e. 720x350, 640x400, etc. There are also enhanced vga cards that can do 800x600 or even 1024x800. On enhanced cards with higher horizontal resolutions, you can usually get more columns in text mode, although sometimes a driver is needed to make it work right. The best deal seems to be using a multisync monitor and an enhanced ega or vga card (depending on how many colors you want - enhanced ega cards usually have as good a resolution as the vga cards). The mitsubishi monitor ($350) I have can do 800x600 pixels max, and many enhanced ega cards can do 800x600. Trying to use 1024x800 will make the corresponding monitor more expensive. Analog vga monitors are expensive, and a multisync monitor can do much more for about the same price. These are only my opinions, drawn from my experience with IBM compatible systems. We have many systems here including Mono, CGA, EGA, enhanced EGA, and VGA. I've also got a frame grabber card that can display 1024x1024 in 256 colors, but I haven't found a monitor that can do that without blowing our budget. :-> Simon Gales@University of Ky {rutgers, uunet}!ukma!simon - simon@ms.uky.edu - simon@UKMA.BITNET ------------------------------ ...... Usually the non-standard feature is better than the IBM standard. For example, I use a 'VGA compatible' which sports both VGA modes and a better 800 X 600 point resolution, but very little software knows how to draw on this higher resolution. Brian Willoughby microsoft!brianw ------------------------------ .... And what "compatible with VGA and EGA" means depend on whether you're talking about a monitor or a display card. From rwmira01@ulkyvx.bitnet Fri Feb 24 20:37:21 1989 Graphics Mode CGA EGA VGA MCGA 320 X 200 4 color X X X X 640 X 200 2 color X X X X 640 X 200 16 color X X 640 X 350 16 color X X 320 X 200 256 color X X 640 X 480 2 color X X 640 X 480 16 color X That is a brief summary of the different modes. If you want more technical insight into the adapters, let me know or read Richard Wilton's Book "Guide to IBM-PC and PS/2 Video Systems" Rob Miracle | Bitnet : RWMIRA01@ULKYVX CIS: 74216,3134 Programmer/Analyst-II | INTERNET : rwmira01%ulkyvx.bitnet@cunyvm.cuny.edu University of Louisville | UUCP : ...psuvax1!ulkyvx.bitnet!rwmira01 ------------------------------ From: bdmrrr.bdm.com!davis@rutgers.uucp (Arthur Davis x4675) .... There is another one called, I believe, PGA (Professional GA). I believe it is capable of 1024 by 768 but am not sure. It is currently IBM PS/2 only I think and not widely supported yet. ------------------------------ From: Yuan 'Hacker' Chang <yuan@uhccux.uhcc.hawaii.edu> -I did not know 'compatible' means different for monitors or adaptors. -Could you give me some information? Let's say you have a display adaptor (say, Video 7's VEGA) that says it's compatible with CGA/EGA/VGA/Hercules, that just means it can do all those modes. So rather than buying four different display adaptors to get the functionality, you just buy one. Compatible has a slightly different meaning for monitors. If a monitor is advertised to be CGA compatible, that means it can only display output from a CGA adaptor. For a multi-sync type monitor, they can sync up to all types of graphic adaptors, therefore they're normally advertised as "CGA/EGA/VGA/Hercules" compatible. I should say that each display adaptor (CGA/EGA/etc.) has its own set of frequencies. Like CGA's horizontal scan freq. is 60Hz, and 15.75kHz vertical. EGA is 70Hz horz. and 15.75kHz Vert.
loving@lanai.cs.ucla.edu (Mike Loving) (03/07/89)
The PGA (Professional Graphics Adapter/Display) was almost entirely absent
from the rather comprehensive post on displays. Since I have one of these
things (no, nobody supports it). I thought I would follow up.
PGA:
640x480 graphics resolution with 256 simultaneously displayed colors
80x25 text (i don't know the colors on this)
It is interesting to note that the resolution is exactly the same as IBM's
VGA with a much greater selection of colors. What is strange is that there
are programs (such as Drafix by Foresight Resources) whose graphics toolkits
support this monitor, but the company did not bother to support it even though
they have laready bought the device independent graphics routines which support
this display. I realize that there are few of us out here with PGA's and the
PGA was way overpriced, but it is really quite a good display and adapter.
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Mike Loving loving@lanai.cs.ucla.edu
. . . {hplabs,ucbvax,uunet}!cs.ucla.edu!loving
-------------------------------------------------------------------------------DPIROT@UALTAVM.BITNET (Don Pirot) (03/09/89)
In article <4339@psuvax1.cs.psu.edu>, deng@shire.cs.psu.edu writes: >The model 30 uses a hybrid display mode called MCGA. It's only available on >the Model 30 and 25 with 8086 processors. It's a modified version of CGA and >hasn't really been supported by developers. t This sort of bothers me in that I went for the Mod 30 before the 30-286 was announced and now I'm wondering if I'm going to be left out on a limb. Does anyone out there know if it is possible to upgrade the Mod 30 to support VGA graphics. As I understand it, my Mod 30 has an analog monitor so it should be able to display VGA graphics. Don Pirot, | BITNET: DPIROT@UALTAVM University Computing Systems, | UUCP: alberta!DPIROT@ualtavm.bitnet University of Alberta, | ARPA: DPIROT%UALTAVM.BITNET@wiscvm.wisc.edu Edmonton, Alberta, Canada. | What luck for rulers that men do not think. | Adolph Hitler (1889-1945)