if iam have 1000$, and i have to build a mining bitcoin rig, what a hardware(gpu), i have must buy?
i mean , a new one,
Honestly, you would probably get a better return spending that money on a direct purchase of bitcoins. Alternately you can wait a few months for some ASIC hardware which should offer a better dollar to performance ratio than any GPU.
However, if you have another use for that graphics card it wouldn't hurt to set it up to mine bitcoins during its downtime. Any recent high end AMD Radeon card will work. If you can find a 6990 or 7950 that would be great. It would be a mistake to think that bitcoin mining can on its own pay for a graphics card anymore.
Alternately for a smaller investment there should be some cheaper used FPGAs on the market now and still cheaper in the not too distant future which are much more energy efficient than GPUs, and are good to play around with if you want to learn some basics about bitcoin mining.
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