Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!zaphod.mps.ohio-state.edu!samsung!olivea!uunet!sam!douglass From: douglass@davidsys.com Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: Dual monitors Message-ID: <8130@davidsys.com> Date: 11 Feb 91 15:55:22 GMT References: <91037.150254BUAD1621@Ryerson.CA> <26753@uflorida.cis.ufl.EDU> <166@cf_su20.cf_su10.Sbi.COM> <26810@uflorida.cis.ufl.EDU> Organization: DAVID Systems Inc, Sunnyvale CA Lines: 50 In article <26810@uflorida.cis.ufl.EDU>, jdb@reef.cis.ufl.edu (Brian K. W. Hook) writes: > In article <166@cf_su20.cf_su10.Sbi.COM> nee@cf_su14.Sbi.Com (Robert Nee) writes: >>> Someone recently posted that if I have a 16-bit VGA card and an 8-bit >>> monochrome card in my system that my VGA will automatically be throttled >>> down to 8-bit...this would become an unacceptable bottleneck in my >>> IO (I have a 386-33). If so, is there a way around it? >>As far as I know there isn't. The solution would be a monochrome >>display adapter with a 16-bit interface. This would allow both >>displays to coexist and operate at full 16-bit speed. But alas >>monochrome is dead... Who would want a 16bit mono board anyway? > I just discovered from someone over at comp.windows.ms.programmer that > supposedly the VGA cards out there all operate at 8-bit bandwidth > when IN GRAPHICS MODE....is this true? Even the 16-bit ones do. I'm afraid that the only ways I know of to get to the graphics memory involve (steps are pseudo-operations): 1) selecting the bit-plane to write to, 2) setting up 8-bit color mask registers on E/VGA card, 3) writing pixels to that color plane, 4) go back to step 1 until all color planes have been updated. Note step 2. I believe that [EV]GA has a hardware limitation in 16-color graphics modes which cripples normal VGA graphics to 8-bit operations. The 256-color modes may not have this problem, I don't know. (Any corrections gladly accepted). Also, I have done some testing of some systems I have available and found no difference in performance to my 16-bit VgaWonder with an IBM monochrome adapter in or out. Testing indicates (on *my* system, YMMV): 16-bit VGA fastest (only text mode tested, of course) 8-bit M[DG]A (or CGA) takes twice as long to write to as 16-bit VGA IBM EGA (8-bit) three times as long as 16-bit VGA These results gathered on 6 and 8 MHz 80286 AT clones, 16 MHz Compaq 386, 16 and 33 MHz 80386 clones. Test consisted of an assembly program that moved screenfuls of data from main memory to the screen 2000 times and counted timer ticks. Sorry to run on so long, but I just can't understand why an 8-bit card should slow down a 16-bit card!?! At least it doesn't in my case. > > Brian -- -{JD}- Jeff (douglass@davidsys.com) /* My opinions are my own. Who else would want them? */ "Never count on the inevitable until it happens. . ." "So therefore a pointer to dev/nul (the nul device) is a NULL pointer?"