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True CGA vs VGA card in CGA mode

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    True CGA vs VGA card in CGA mode

    Hi all

    Is there any performance differences between a true CGA card and a 8-bit VGA card running CGA graphics ?
    Current machines:
    PCs: IBM PC XT 640K, IBM PC XT 256K ,IBM PC XT , 2x IBM PC AT, Compaq Portable I, Compaq Portable II, Compaq Portable I/286, Philips Logic Analyzer XT clone, IBM PS/2 Model 30 286 , HP 95X, HP200LX (2x),Compaq SLT/286.
    Apple: Macintosh 512k, Macintosh SE, Macintosh Classic, PowerBook 170, iBook Clamshell, iBook G3,iMac G4 , TiBook's, Apple IIc, Many newer machines (G4, G5, Intel..), 20th Anniversary Mac
    Others: Commodore 64C,Amiga A500, CCS S-100 System, SNES,

    Wanted: Macintosh 128k, Hard Disk 20, System disks and games for the Mac

    #2
    If it has switches so it oculd be toggeled to CGA mode on startup, it would operate as a CGA, and there would be no differences unless the card is of lower quality and price.

    However, if it's configured as VGA on startup, it might have some problems with certain CGA graphics modes.
    Current systems owned by me:
    Vintage:IBM PC/XT submodel 087 ( 1983 ), [Kon]tiki-100 rev. C (1983), Compaq Portable I ( 1984 ), IBM PC/XT submodel 078 ( 1985 ), IBM PC/XT286 ( ~1986 ), 3x Nintendo Entertainement Systems ( 1987 ).
    Obsolete:Commodore A500 ( ~1990 ), IBM PS/2 model 70/386 type 8570-161 ( 1991 ), Atari Lynx II ( ~1992 ), Generic Intel 486SX PC ( ~1993 ), AT/T Globalyst Pentium w/FDIV bug MB ( 1994 ), Compaq 486DX4 laptop ( ~1995 ).

    Comment


      #3
      memory map

      Well, they typically live at different addresses in the pc's address space.
      0A0000-0AFFFF VGA/EGA Video Memory
      0B0000-0B0FFF Monochrome Video Memory
      0B8000-0BFFFF CGA

      patscc

      Comment


        #4
        Originally posted by patscc View Post
        Well, they typically live at different addresses in the pc's address space.
        0A0000-0AFFFF VGA/EGA Video Memory
        0B0000-0B0FFF Monochrome Video Memory
        0B8000-0BFFFF CGA

        patscc
        Okay. I was thinking more along the line: If I run a game in CGA on a VGA card or run it on a true CGA card, will there be any noticeable performance differences ?

        I talk simple games, like Alley Cat
        Current machines:
        PCs: IBM PC XT 640K, IBM PC XT 256K ,IBM PC XT , 2x IBM PC AT, Compaq Portable I, Compaq Portable II, Compaq Portable I/286, Philips Logic Analyzer XT clone, IBM PS/2 Model 30 286 , HP 95X, HP200LX (2x),Compaq SLT/286.
        Apple: Macintosh 512k, Macintosh SE, Macintosh Classic, PowerBook 170, iBook Clamshell, iBook G3,iMac G4 , TiBook's, Apple IIc, Many newer machines (G4, G5, Intel..), 20th Anniversary Mac
        Others: Commodore 64C,Amiga A500, CCS S-100 System, SNES,

        Wanted: Macintosh 128k, Hard Disk 20, System disks and games for the Mac

        Comment


          #5
          Originally posted by QuantumII View Post
          Okay. I was thinking more along the line: If I run a game in CGA on a VGA card or run it on a true CGA card, will there be any noticeable performance differences ?

          I talk simple games, like Alley Cat
          I have had some problems with that. Often, the VGA is toggeled into wrong video modes, ant it doesn't really support some of the special modes of the CGA, like some of the CGA's graphics mode, like morecolors and the BG/red/cyan/white palette.

          See the attachement of running Flightsimulator 2.13 (Booter) on a VGA in VGA mode and VGA in CGA mode. Note that "Signal Error" alert in the upper right courner on one of the pictures, hence, NOT recomended on CRT monitors.
          Last edited by per; April 28, 2009, 04:10 AM.
          Current systems owned by me:
          Vintage:IBM PC/XT submodel 087 ( 1983 ), [Kon]tiki-100 rev. C (1983), Compaq Portable I ( 1984 ), IBM PC/XT submodel 078 ( 1985 ), IBM PC/XT286 ( ~1986 ), 3x Nintendo Entertainement Systems ( 1987 ).
          Obsolete:Commodore A500 ( ~1990 ), IBM PS/2 model 70/386 type 8570-161 ( 1991 ), Atari Lynx II ( ~1992 ), Generic Intel 486SX PC ( ~1993 ), AT/T Globalyst Pentium w/FDIV bug MB ( 1994 ), Compaq 486DX4 laptop ( ~1995 ).

          Comment


            #6
            Originally posted by per View Post
            I have had some problems with that. Often, the VGA is toggeled into wrong video modes, ant it doesn't really support some of the special modes of the CGA, like some of the CGA's graphics mode, like morecolors and the BG/red/cyan/white palette.

            See the attachement of running Flightsimulator 2.13 (Booter) on a VGA in VGA mode and VGA in CGA mode. Note that "Signal Error" alert in the upper right courner on one of the pictures, hence, NOT recomended on CRT monitors.
            Galaxian is one game I know that does this. It works on some VGA monitors, but on others the picture loses sync.

            Moon Patrol always locks up about 7 seconds into the game (Demonlord noted this on his site). Both of these games have some kind of problem with VGA, but I'm not sure what.

            VGA is BIOS compatible with CGA, but not register compatible. At least 60% of CGA software works on VGA, but the other 30% either partially or completely fails. This can be caused by any of the following:

            *Setting video modes or color palettes by writing directly to the registers

            *Using the 160x100 pseudographics mode

            *Raster interrupts

            *Tweaking the 6845 registers to produce effects like screen shaking

            Comment


              #7
              Originally posted by per View Post
              I have had some problems with that. Often, the VGA is toggeled into wrong video modes, ant it doesn't really support some of the special modes of the CGA, like some of the CGA's graphics mode, like morecolors and the BG/red/cyan/white palette.

              See the attachement of running Flightsimulator 2.13 (Booter) on a VGA in VGA mode and VGA in CGA mode. Note that "Signal Error" alert in the upper right courner on one of the pictures, hence, NOT recomended on CRT monitors.
              Yeah, I tried FS on VGA, and it was just like your picture.. Say, did you boot the game from a floppy or did you run the fs.com file ?
              Current machines:
              PCs: IBM PC XT 640K, IBM PC XT 256K ,IBM PC XT , 2x IBM PC AT, Compaq Portable I, Compaq Portable II, Compaq Portable I/286, Philips Logic Analyzer XT clone, IBM PS/2 Model 30 286 , HP 95X, HP200LX (2x),Compaq SLT/286.
              Apple: Macintosh 512k, Macintosh SE, Macintosh Classic, PowerBook 170, iBook Clamshell, iBook G3,iMac G4 , TiBook's, Apple IIc, Many newer machines (G4, G5, Intel..), 20th Anniversary Mac
              Others: Commodore 64C,Amiga A500, CCS S-100 System, SNES,

              Wanted: Macintosh 128k, Hard Disk 20, System disks and games for the Mac

              Comment


                #8
                Originally posted by QuantumII View Post
                Yeah, I tried FS on VGA, and it was just like your picture.. Say, did you boot the game from a floppy or did you run the fs.com file ?
                I booted from a floppy (from retrogade, that one got no hidden message on it).

                You say you got a CGA with a RCA jack. If you got a monitor/TV capable of displaying NTSC, you could connect it to the CGA. FS is a lot better in composite than RGBI.
                Current systems owned by me:
                Vintage:IBM PC/XT submodel 087 ( 1983 ), [Kon]tiki-100 rev. C (1983), Compaq Portable I ( 1984 ), IBM PC/XT submodel 078 ( 1985 ), IBM PC/XT286 ( ~1986 ), 3x Nintendo Entertainement Systems ( 1987 ).
                Obsolete:Commodore A500 ( ~1990 ), IBM PS/2 model 70/386 type 8570-161 ( 1991 ), Atari Lynx II ( ~1992 ), Generic Intel 486SX PC ( ~1993 ), AT/T Globalyst Pentium w/FDIV bug MB ( 1994 ), Compaq 486DX4 laptop ( ~1995 ).

                Comment


                  #9
                  How about a CGA with a scan converter box (as discussed on other threads?). I assume the idea is to use a VGA monitor.

                  Comment


                    #10
                    Originally posted by Chuck(G) View Post
                    How about a CGA with a scan converter box (as discussed on other threads?). I assume the idea is to use a VGA monitor.
                    Yes, if I cannot get a CGA monitor within reasonable time (I'm an impatient guy sometimes) I'll get one of those.. They could be nice to have anyway
                    Current machines:
                    PCs: IBM PC XT 640K, IBM PC XT 256K ,IBM PC XT , 2x IBM PC AT, Compaq Portable I, Compaq Portable II, Compaq Portable I/286, Philips Logic Analyzer XT clone, IBM PS/2 Model 30 286 , HP 95X, HP200LX (2x),Compaq SLT/286.
                    Apple: Macintosh 512k, Macintosh SE, Macintosh Classic, PowerBook 170, iBook Clamshell, iBook G3,iMac G4 , TiBook's, Apple IIc, Many newer machines (G4, G5, Intel..), 20th Anniversary Mac
                    Others: Commodore 64C,Amiga A500, CCS S-100 System, SNES,

                    Wanted: Macintosh 128k, Hard Disk 20, System disks and games for the Mac

                    Comment


                      #11
                      Hi

                      Today I did some tests (True CGA card VS VGA Card in CGA mode)

                      Results: The true CGA card was faster and the graphics was smoother.

                      Alley Cat is choppy when running ona VGA card (Many items on screen, bad performance)

                      When using a true CGA card is was running along just fine, regardless of the items on screen etc etc..

                      How come ? Anyone seen it before ?
                      Current machines:
                      PCs: IBM PC XT 640K, IBM PC XT 256K ,IBM PC XT , 2x IBM PC AT, Compaq Portable I, Compaq Portable II, Compaq Portable I/286, Philips Logic Analyzer XT clone, IBM PS/2 Model 30 286 , HP 95X, HP200LX (2x),Compaq SLT/286.
                      Apple: Macintosh 512k, Macintosh SE, Macintosh Classic, PowerBook 170, iBook Clamshell, iBook G3,iMac G4 , TiBook's, Apple IIc, Many newer machines (G4, G5, Intel..), 20th Anniversary Mac
                      Others: Commodore 64C,Amiga A500, CCS S-100 System, SNES,

                      Wanted: Macintosh 128k, Hard Disk 20, System disks and games for the Mac

                      Comment


                        #12
                        Originally posted by QuantumII View Post
                        Hi

                        Today I did some tests (True CGA card VS VGA Card in CGA mode)

                        Results: The true CGA card was faster and the graphics was smoother.

                        Alley Cat is choppy when running ona VGA card (Many items on screen, bad performance)

                        When using a true CGA card is was running along just fine, regardless of the items on screen etc etc..

                        How come ? Anyone seen it before ?
                        The VGA's ability to emulate CGA isn't 100% perfect. my guess it that it varys from card to card. Also VGA uses other registers, so if the program does low-level stuff (IN/OUTs), then it might write to other registers than it is supposed to. Another cause can be that the version program you're using is modified for newer computers (most unlikely).
                        Current systems owned by me:
                        Vintage:IBM PC/XT submodel 087 ( 1983 ), [Kon]tiki-100 rev. C (1983), Compaq Portable I ( 1984 ), IBM PC/XT submodel 078 ( 1985 ), IBM PC/XT286 ( ~1986 ), 3x Nintendo Entertainement Systems ( 1987 ).
                        Obsolete:Commodore A500 ( ~1990 ), IBM PS/2 model 70/386 type 8570-161 ( 1991 ), Atari Lynx II ( ~1992 ), Generic Intel 486SX PC ( ~1993 ), AT/T Globalyst Pentium w/FDIV bug MB ( 1994 ), Compaq 486DX4 laptop ( ~1995 ).

                        Comment


                          #13
                          Originally posted by per View Post
                          The VGA's ability to emulate CGA isn't 100% perfect. my guess it that it varys from card to card. Also VGA uses other registers, so if the program does low-level stuff (IN/OUTs), then it might write to other registers than it is supposed to. Another cause can be that the version program you're using is modified for newer computers (most unlikely).
                          Okay. I think it's because _some_ emulation are taking place, native CGA will have better performance. The 4.77Mhz is not that much, and the hardware overhead of doing the emulating affects the performance for programs written for pure CGA.

                          Of course, on newer PC's this is not noticeable (I tried) but the IBM's limited speed in combination with the above is the reason (I think)

                          I have now bought an original IBM CGA card off eBay. I will use that instead when I a) Get an IBM 5153 or b) Get a cga-to-vga converter or c) get an LCD with composite in..

                          I think option b is most likely right now, but I will continue to hunt for an IBM 5153.
                          Current machines:
                          PCs: IBM PC XT 640K, IBM PC XT 256K ,IBM PC XT , 2x IBM PC AT, Compaq Portable I, Compaq Portable II, Compaq Portable I/286, Philips Logic Analyzer XT clone, IBM PS/2 Model 30 286 , HP 95X, HP200LX (2x),Compaq SLT/286.
                          Apple: Macintosh 512k, Macintosh SE, Macintosh Classic, PowerBook 170, iBook Clamshell, iBook G3,iMac G4 , TiBook's, Apple IIc, Many newer machines (G4, G5, Intel..), 20th Anniversary Mac
                          Others: Commodore 64C,Amiga A500, CCS S-100 System, SNES,

                          Wanted: Macintosh 128k, Hard Disk 20, System disks and games for the Mac

                          Comment


                            #14
                            Snow

                            I seem to remember having to twiddle with timings when writing CGA code to minimize snow. That might be why some games look odd on VGA-emulated CGA, since I don't think you get the CGA snow problem on VGA cards. Although I certainly could be wrong.

                            patscc

                            Comment


                              #15
                              Originally posted by QuantumII View Post
                              Okay. I think it's because _some_ emulation are taking place, native CGA will have better performance. The 4.77Mhz is not that much, and the hardware overhead of doing the emulating affects the performance for programs written for pure CGA.
                              I've run CGA games on my 386 with the turbo off, and I don't notice any performance problems. Alley Cat doesn't use any weird video tricks either, so there's no real difference between running it on a CGA or a VGA card (you do have to run it at 4.77Mhz to hear the digitized sound effects, though).

                              Originally posted by QuantumII View Post
                              I have now bought an original IBM CGA card off eBay. I will use that instead when I a) Get an IBM 5153 or b) Get a cga-to-vga converter or c) get an LCD with composite in..
                              I have a CGA card too, but I don't yet have a working 5150 or XT to put it in.

                              Comment

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