True CGA vs VGA card in CGA mode

[QuantumII]

Hi all

Is there any performance differences between a true CGA card and a 8-bit VGA card running CGA graphics ?

 

[per]

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.

 

[patscc]

memory map

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

 

[QuantumII]

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

 

[per]

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.

 

[Fallo]

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

 

[QuantumII]

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 ?

 

[per]

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.

 

[Chuck(G)]

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

 

[QuantumII]

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

 

[QuantumII]

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 ?

 

[per]

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).

 

[QuantumII]

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.

 

[patscc]

Snow

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

 

[Fallo]

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).

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.

 

[QuantumII]

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).



I have a CGA card too, but I don't yet have a working 5150 or XT to put it in.

The difference is there, trust me

Regarding the 5150:
Ebay has a few listed now, but it's not exactly mint condition units...

 

[Fallo]

The difference is there, trust me

Regarding the 5150:
Ebay has a few listed now, but it's not exactly mint condition units...

That's usually the case. About two weeks ago, there was one 5150 on there that was a real scream. The seller's description was simply "IBM 5150", accompanied by one picture of the computer. There were no images of the back or the inside, and no information as to whether the computer worked or not, what cards were in it, or if it was a 16k-64k or a 64k-256k model. As you can well imagine, the auction ended without any takers.

 

[QuantumII]

That's usually the case. About two weeks ago, there was one 5150 on there that was a real scream. The seller's description was simply "IBM 5150", accompanied by one picture of the computer. There were no images of the back or the inside, and no information as to whether the computer worked or not, what cards were in it, or if it was a 16k-64k or a 64k-256k model. As you can well imagine, the auction ended without any takers.

Hehe yeah, I know the kind. When the tools cannot even take proper pictures or try to describe the item they don't want it to get sold. (usually such items are also overpriced)

 

[hargle]

I've found this thread to be really interesting, especially the differences noted in both alley cat and FS.

I'm wondering if someone (trixter perhaps?) could put together a small program/benchmark program to help us quickly and easily know the differences between true CGA and VGA, and that could then help us figure out what the best VGA card is to use on our machines. I have a half dozen ISA VGA cards and I have no idea which one might give me the best CGA performance for the buck.

 

[QuantumII]

I've found this thread to be really interesting, especially the differences noted in both alley cat and FS.

I'm wondering if someone (trixter perhaps?) could put together a small program/benchmark program to help us quickly and easily know the differences between true CGA and VGA, and that could then help us figure out what the best VGA card is to use on our machines. I have a half dozen ISA VGA cards and I have no idea which one might give me the best CGA performance for the buck.

Second that. Such an utility would be very useful. This also allows us to check the difference between different CGA cards as well