http://www.penstarsys.com/#xfire_sil
here josh trys to explain why the supposed limitation may not be a limitation at all
credit to JBT for this
from a post i made in rollos thread..........
"good catch....reading now
hmm it makes sense but theres still trade offs, hes talking about blanking, and goes on to explain that only half the bandwidth is needed anyway in scissor mode. Atis scissor mode will be just like NV's SFR (only not dynamic, therefore needing to be pre programmed per game) which isnt used a an awful lot. AFR is best because of geometry scaling and with AFR u need to transport the whole image so the bottleneck still stands
will read it a few times though to get my head round it
Let's move on to a higher end CRT or LCD that can display 2048x1536. In Scissor mode each card has to render 2048x768 pixels, and at 60 Hz that comes out to be 94 Mpps. Again, this is well below the maximum 115 Mpps that the receiver can handle. The maximum fps that the receiver can handle in this mode is 73 fps. While this is short of the 75 fps that is needed to run with v-sync enabled at 75 Hz, it isn't terribly far off either! Most users will not notice much of a difference (this is again assuming the cards can run the application at that speed).
i mean scissor mode at that hi-res and you cant run 75Hz if you want to for Vsync. i know refresh really is a non issue on LCD's but people do like to have higher refreshes. and when vsyncs involved then it really is a difference between 60fps and 75 fps. hes going by theory which he has no choice but to, but theory doesnt always = practice
Now, things do change around a bit when using alternating frames. At 1920x1200 the receiver can handle a maximum of 50 fps (1920x1200 at 50 Hz, assuming the Sil chip can be programmed as such). At 2048x1536 the maximum rate is 37 fps (2048x1536 at 37 Hz). In alternating frame mode the CrossFire solution will have a max FPS of 100 when used at 1920, or a max FPS of 75 when used with 2048. We are essentially just dealing with bandwidth, as the pixel information transmitted basically contains color information (RGB) and location (clock). As such, the ways with dealing with this information can be pretty flexible. This of course assumes that the Sil 1161 is running at 165 MHz all the time.
now here hes assuming that you can up the res and drop the frequency, but we dont know that for sure. if it can then looks like crossfire will be able to provide 2048x1536@ 75Hz
so good assumptions and theory, just need to wait and find out if they are correct "
EDIT UPDATE
see wreckages post below. but basically josh has recieved some 3rd party info that lays to rest his theorys.
the 3rd party reported they couldnt achieve any higher than 16x12 @ 60hz on a CRT
Things are getting more and more interesting as time goes on...
I have received some 3rd party confirmation that testers with CrossFire rigs can't in fact get above 1600x1200 @ 60 Hz with CRTs.
Something else to consider is that the Compositing chip doesn't appear to have built in RAMDACs or a TMDS transmitter, so has to use external ones. From what we are starting to see, it might just be the lack of high quality, built in RAMDACs or TMDSs that is limiting the solution to 1600x1200 60 Hz. If this is the case, ATI is indeed in big trouble as there are certain things you just can't work around.
here josh trys to explain why the supposed limitation may not be a limitation at all
credit to JBT for this
from a post i made in rollos thread..........
"good catch....reading now
hmm it makes sense but theres still trade offs, hes talking about blanking, and goes on to explain that only half the bandwidth is needed anyway in scissor mode. Atis scissor mode will be just like NV's SFR (only not dynamic, therefore needing to be pre programmed per game) which isnt used a an awful lot. AFR is best because of geometry scaling and with AFR u need to transport the whole image so the bottleneck still stands
will read it a few times though to get my head round it
Let's move on to a higher end CRT or LCD that can display 2048x1536. In Scissor mode each card has to render 2048x768 pixels, and at 60 Hz that comes out to be 94 Mpps. Again, this is well below the maximum 115 Mpps that the receiver can handle. The maximum fps that the receiver can handle in this mode is 73 fps. While this is short of the 75 fps that is needed to run with v-sync enabled at 75 Hz, it isn't terribly far off either! Most users will not notice much of a difference (this is again assuming the cards can run the application at that speed).
i mean scissor mode at that hi-res and you cant run 75Hz if you want to for Vsync. i know refresh really is a non issue on LCD's but people do like to have higher refreshes. and when vsyncs involved then it really is a difference between 60fps and 75 fps. hes going by theory which he has no choice but to, but theory doesnt always = practice
Now, things do change around a bit when using alternating frames. At 1920x1200 the receiver can handle a maximum of 50 fps (1920x1200 at 50 Hz, assuming the Sil chip can be programmed as such). At 2048x1536 the maximum rate is 37 fps (2048x1536 at 37 Hz). In alternating frame mode the CrossFire solution will have a max FPS of 100 when used at 1920, or a max FPS of 75 when used with 2048. We are essentially just dealing with bandwidth, as the pixel information transmitted basically contains color information (RGB) and location (clock). As such, the ways with dealing with this information can be pretty flexible. This of course assumes that the Sil 1161 is running at 165 MHz all the time.
now here hes assuming that you can up the res and drop the frequency, but we dont know that for sure. if it can then looks like crossfire will be able to provide 2048x1536@ 75Hz
so good assumptions and theory, just need to wait and find out if they are correct "
EDIT UPDATE
see wreckages post below. but basically josh has recieved some 3rd party info that lays to rest his theorys.
the 3rd party reported they couldnt achieve any higher than 16x12 @ 60hz on a CRT
Things are getting more and more interesting as time goes on...
I have received some 3rd party confirmation that testers with CrossFire rigs can't in fact get above 1600x1200 @ 60 Hz with CRTs.
Something else to consider is that the Compositing chip doesn't appear to have built in RAMDACs or a TMDS transmitter, so has to use external ones. From what we are starting to see, it might just be the lack of high quality, built in RAMDACs or TMDSs that is limiting the solution to 1600x1200 60 Hz. If this is the case, ATI is indeed in big trouble as there are certain things you just can't work around.
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