I can see in whattomine.com, there showing 110% profit in 7 days.
what machine will be better for EthereumClassic(ETC) ?
The 110% just means that in a particular period it was 10% more profitable to mine than the preceding period compared to ETHEREUM. So its 10% more profitable but the profitability is still pretty bad.
Take a RX 470 4GB for example, it hashes at like 28MH/s using 130 Watts and makes $0.24 per day before electric, the 10% extra is only an extra $0.024. And if you got power higher than $0.08/kwh you are pretty much not making anything.
The ETH profitability will be 30% or so more profitable on January 1st when they delay the ice age and we get 13 second block times again.
+1
anyway i think we must give him "the real ROI calculation too
today the "old grapic card" like Rx 470, Rx480 verycheap but the problem is 80% of them is 2nd hand from miner and i can't say the ROI will come before the machine dead
The cards are very cheap but they are not that old. They came out when? Summer 2016, so they are about 3 years old. However the RX 570 is even newer. I had many of these GPUs and didn't have a single one that failed, the only issue I had with some were the fans. The bearings started to make noise and eventually the fans died. However I either re-oiled those fans or just bought some replacement fans from eBay/Amazon.
Same with my older GPUs like the Radeon 7970, they came out in 2012/2013, and I used many of them in late 2017 and many still worked fine. Same issues as before with dead fans but the GPUs themselves were bulletproof. And they actually used more wattage than the RX series so they were put thru more stress.
Nothing wrong with second hand GPUs, much smarter than buying a new GPU for mining.
