All About BTC, LTC, ETH mining as well as other alternative crypto currencies
The GeForce GTX 750 Ti series of graphics cards based no the new Nvidia Maxwell architecture have really captured the attention of crypto currency miners due to their good performance (hashrate) per watt. Nvidia is advertising these cards to have 60W TDP, however we have discovered that the actual TDP limit for the power target set in the video BIOS of these cards is 38.5W…
This made us dig into the matter a bit more in order to see how much power actually does a GeForce GTX 750 Ti draw from the motherboard (a reference GT 750 with no external PCI-E power connector). So we’ve attached a watt meter to the power line of an external PCI-E extender to see how much power is drawn by the GT 750 Ti card. The results we got were quite surprising, even though we knew that the default power consumption should fit in the 38.5W limit for the power target set in the BIOS. With the stock frequencies for the GPU and the video memory the GeForce GTX 750 Ti has shown to draw just about 28W ot power producing about 250 KHS hashrate for Scrypt mining. After getting the card overclocked to +135 MHz for the GPU and +650 MHz for the video memory the power consumption has risen a bit to about 34W average with a hashrate of about 300 KHS for Scrypt crypto mining.
So if you were calculating the power usage of GTX 750 Ti as 60W in order to see the ratio of hashrate per Watt of power, then you should rethink how you calculate it now. Note that this is the actual power that goes from the PSU to the video card, the real power consumption with a 80 Plus certified power supply that provides 90% efficiency for example would rise with 10% to about 30W (stock) and 37W (overclocked) respectively as the actual power drawn by the card from the wall socket.
Nvidia is advertising their new GeForce GTX 750 Ti GPUs based on the new more power efficient Maxwell architecture as being with 60W TDP, but in truth they seem to be much more power efficient than that. A lot of people are already interested in using these new GPUs from NVidia for mining, because the performance that the Maxwell delivers seems to be very good in terms of hashrate per Watt ratio. When you use CUDAminer to mine with the GTX 750 Ti you will notice the card will quickly reach the 100% power target limit and normally you are not allowed to increase the power limiter of the card above the 100% value, you are allowed to only lower it further. The interesting thing here however is that the default TDP limit for GTX 750 Ti is actually set to 38.5W inside the BIOS and the minimum of 78% you can go down to is equal to just 30W TDP and as we’ve mentioned Nvidia is talking about 60W TDP for these cards. The fact that the cards are actually limited to 38.5W by their power limiter is something that can prevent you from squeezing the maximum performance that you can get by overclocking the GPU and/or the video memory of the card, so increasing the TDP limit by modifying the BIOS and reflashing the video card with the modified BIOS can help you with that.
Since many of the GeForce GTX 750 Ti video cards do not have external PCI-E power connector you will be limited to the maximum power that these cards will be able to use due to the 75W maximum of power that PCI-E x16 slot can provide by specifications (66W for the 12V line that you will be actually using, the other ~10W are for the 3.3V line). But even this will provide more than enough headroom since the default TDP limit is not 60W as we though, but really just 38.5W, so lots of headroom for overclocking. In order to be able to modify the BIOS of your video card you will need to first save the original one from the card, you can use GPU-Z for that and make sure you keep the original BIOS as a backup and save the modified one as a separate file (you can also backup the BIOS with the nvflash under DOS if you are having trouble with GPU-Z). Then you need to fire up Kepler Bios Tweaker and open up your BIOS file and edit is as shown in the screenshot above (left is original, right is the modified) in order to get 65.5W as the maximum TDP of the card. After that you need to flash the BIOS back to your card using the provided nvflash, you can download the flasher and the Kepler Bios Tweaker along with a standard BIOS from a reference 750 Ti and a modified version of that BIOS to allow 65.5W TDP from the link below. We suggest that you save the BIOS from your own video card and modify it, also do have in mind that modifying and flashing modified video BIOS to your video card can be dangerous, so you should be extra careful what you are doing and not modifying things that you should not or does not know what they are for!
The procedure described above will work for increasing the power target limit on other video cards as well not only on GTX 750 Ti, however before increasing the limit make sure that your video card cooling can keep the card cool enough. Using the video card fro mining will bring the power target to 100% in most cases even without overclocking the card additionally, so just by increasing it you might e able to squeeze some extra performance even without overclocking it further. The version of nvflash provided in the archive below is the latest one that will work with the GTX 750 Ti as well as with older video cards, it is the DOS version of the flasher as the Windows version of nvlfash does not seem to work properly – it does not want to flash the modified BIOS to the card saying that the BIOS digital signature is wrong. No problems flashing the modified video BIOS though trough the DOS version of nvflash 5.163, so we have only included the DOS version that will work with the method described above. There are two BAT files configured to flash the modified video BIOS and to restore the original version of the included reference design board BIOSes, you just need to run “nvflash your_bios.rom” and confirm with “y” when asked by nvflash (make sure you’ve made a backup of your original video BIOS first!). Again, be aware that video BIOS flashing and modification can be dangerous and can temporary render your video card useless, at least until you reflash it with the original BIOS, so do keep a backup of the original! Also note that increasing the TDP limit beyond the recommended value above could also be dangerous, so be well aware that this modification can be dangerous! Feel free to share your results for overclocking and mining hashrate after increasing the TDP limit of your GTX 750 Ti or another board in the comments below.
We have already ran some tests of the new GeForce GTX 750 Ti GPU based on the new Nvidia Maxwell architecture for mining scrypt-based crypto currencies such as LTC and DOGE with the help of CUDAminer (up to 265 KHS). The results it is giving, along with the low power usage of the card are making it an interesting option for people that are interested in mining crypto currencies with Nvidia GPUs. The GeForce GTX 750 Ti also shows good overclocking potential for even higher performance (up to about 300 KH/s) on a reference design board. After looking at some non-reference design boards such as ASUS GTX750TI-OC-2GD5 that has additional PCI-E power connector and much better cooling we considered that even higher performance could be achieved, however after checking some reviews of these cards it seems that the Power Target maximum on these cards is still 100%. This simply means that even though the card is clearly designed to handle serious overclocking, the power limiter will not allow you to go beyond the TDP rating of 60W, so as a result it seems that these cards are not overclocking much better than the standard reference boards.
We have also tested the performance that the new GeForce GTX 750 Ti Maxwell cards can offer in some other crypto currencies supported by CUDAminer that do not use Scrypt algorithm, but instead rely on different approaches – SHA-3 (Keccak), Scrypt-jane, Adaptive N factor Scrypt. The performance we got with them was also quite good, though overclocking the card did not help as much these as with Scrypt. Below you can find out what our results were with the different crypto coins we have tried that use the above mentioned alternative algorithms. Note that we are still trying out different configurations in order to get the maximum performance out of the GTX 750 Ti for these alternative crypto currencies, so any suggestions for settings to try with are welcome. As suggested we overclocked only the GPU for the latest results to the maximum of +135 MHz, without clocking the video memory as apparently for these algorithms it does not make sense (downclocking it down with -502 MHz does not seem to affect performance significantly). We are going to update the results if/when we get a better performance with the settings we find to work best for the specific algorithm and crypto coin combination. You are also welcome to request us to test with other coins that are supported by the CUDAminer software.
YACoin Scrypt-jane mining performance with:
cudaminer.exe -a scrypt-jane -o stratum+tcp://yac.coinmine.pl:9088 -u yourworker.1 -p password -L 4
Mining YACoin that uses Scrypt-jane has proven a bit tricky with CUDAminer as apparently it did not want to work properly with our custom settings for the kernel settings we used for Scrypt, the only way to make it work was to use the autotune functionality of the miner, otherwise we were getting errors. This means that we could not try our best performing kernel configuration T5x24 on Scrypt-jane here. After trying some suggestions for CUDAminer and YACoin and adding lookup gap with -L 4 (the best performing lookup gap setting for GTX 750 Ti) we got around 1.7 KHS out of the card. Overclocking the GTX 750 Ti to +150 MHz GPU gets us up to about 1.78 KHS of hashrate for mining YACoin (T74x1 automatically selected, so far has the best performance, as setting manually kernel does not appear to work properly).
VTC Adaptive N factor Scrypt mining performance with:
cudaminer.exe -a scrypt:2048 -o stratum+tcp://stratum.vertco.in:8080 -u yourworker.1 -p password -i 0 -l T5x24 -C 1 -H 2
For VTC mining that uses Adaptive N factor Scrypt algorithm with the T5x24 configuration and manual settings got us about 125-129 KHS hashrate with the GTX 750 Ti running at stock frequencies. After overclocking the Maxwell to +135 MHz GPU the performance increase has boosted our hashrate to about 135-137 KHS.
MaxCoin Keccak mining performance with:
cudaminer.exe -a keccak -o stratum+tcp://maxpool.1gh.com:17333 -u mGeS2LBCTJvz1Mb4Hfzt5fU1C9C1tYrxuY -p password -i 0 -l K1000x24 -C 1 -H 0
For MaxCoin mining that uses Keccak (SHA-3) algorithm we could also use the K1000x24 kernel configuration and manual settings and that got us about 62000 KHS hashrate with the GTX 750 Ti running at default clocks. Overclocking the GTX 750 Ti to +135 MHz GPU has increased a bit the hashrate to about 72600 KHS.
Meanwhile the author of CUDAminer has released an updated version of the miner software, though it is not yet specially optimized for the new Maxwell architecture you might want to update to it as it has some fixes and improvements. Furthermore there is a mention about upcoming BlakeCoin (BLC) support, so it will be interesting to see what kind of performance the GTX 750 Ti will be able to offer for BLC mining (Blake-256 algorithm) where the typical hashrate is about 3x the one you get when Scrypt mining.