--- Jeff Walther <[EMAIL PROTECTED]> wrote: <clip> > There may be dual ported asynchronous graphics chips > around that > could be adapted, but any parts of that type are > most likely not being manufactured any more.
Large numbers of PC videocards made after the original CGA ones had dual ported RAM. CGA used ordinary DRAM and had no buffers. To avoid "snow" on the screen the default state was to wait one cycle between all reads and writes. Fortunately this was left "open" so that software could set the card to not wait at all in text modes. Spurious underscore characters would randomly "blip" onscreen here and there, but only when large amounts of text was changing on the screen, like when fast scrolling. Never bothered me! :) IBM built a small buffer into the EGA design to eliminate the problem. ===== It's total Fandemonium! http://www.fandemonium.org __________________________________ Do you Yahoo!? Win a $20,000 Career Makeover at Yahoo! HotJobs http://hotjobs.sweepstakes.yahoo.com/careermakeover -- Vintage Macs is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Enter To Win A | -- Canon PowerShot Digital Cameras start at $299 | Free iBook! | Support Low End Mac <http://lowendmac.com/lists/support.html> Vintage Macs list info: <http://lowendmac.com/lists/vintagemacs.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/vintage.macs%40mail.maclaunch.com/> Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
