Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!elroy.jpl.nasa.gov!decwrl!sgi!shinobu!odin!westworld.esd.sgi.com!erik From: erik@westworld.esd.sgi.com (Erik Fortune) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: Mentor & Trident VGA cards - which one is the best ? Message-ID: <1991Apr9.004129.20991@odin.corp.sgi.com> Date: 9 Apr 91 00:41:29 GMT References: <1991Apr3.071713.6290@fel.tno.nl> <3725@d75.UUCP> <1991Apr6.192215.29729@leland.Stanford.EDU> Sender: news@odin.corp.sgi.com (Net News) Reply-To: erik@westworld.esd.sgi.com (Erik Fortune) Organization: Silicon Graphics Inc. Lines: 46 The ET4000 allows you to map the entire 1-meg frame buffer in high memory somewhere, which means you don't have to fool around with segment registers to use the memory intensive modes. On the other hand, doing so eats a meg of high memory. I don't have specs in front of me, but I assume the ET4000 has distinct read and write segments (most do), so you can do screen to screen copies directly if you decide to stick with 64k segments. If I want to copy from scanline 64 (in segment 1) to scanline 63 (in segment 0), I can simply set my read segment to 1, my write segment to 0 and copy the bytes. The Trident 8900 can do 128k segments which is good for 1024x768x16 because it eliminates the need to switch segments (assuming you have the memory space available). Segment and mode switching is a little arcane, but once you get past your disbelief it's not too hard to make it work. The 8900's worst misfeature is that is has a single segment register for both read and write. If I want to copy from scanline 64 (in segment 1) to scanline 63 (in segment 0), I have to set my segment register to 1, read the data I want into temporary memory, set my segment register to 0 and finally copy the data from temporary memory back into the frame buffer. These extra steps slow down screen to screen copies (like scrolling) substantially. Summary: In 4 plane (16 color) modes, the trident and tseng chips should be comparable. I haven't measured them, but I'd expect things like clock and memory speed to affect performance at least as much as the chipset does -- probably more. In 8 plane (256 color) modes, the ET4000 is a pretty clear winner in terms of amount of overhead and code complexity. I don't know the relative speeds of the two chipsets, but all of the extra segment messiness has to slow you down on the 8900. I run X on a trident vga card at home (in 1024x768x16 colors), and it's pretty speedy and reliable. When I get around to porting a full 256 color server for the VGA, I'll probably buy a Tseng-based adapter to avoid all of that segment garbage. Hope this helps, Erik