Can't seem to mine with GPU : Bitcoin

A few questions about BitCoin Mining

My computer currently gets like 20MHash/s. I am debating whether or not to get an ATI 6990 because it supposedly gets 700, which with my rough math, should get like .0392 BTC a day, or currently roughly $4.90 USD. If I get a BitForce SC that gets 4.5-5GHash/s, I'd be getting .25 BTC a day, or roughly $34 USD per day. If I get four of them, that's like 1 BTC or $136 USD a day.
I'm just a little weary, as in if someone could make machines to make that much BTC a day, why'd they sell them? Also, it seems as thought this money is coming out of thin air. If I understand correctly, but I guess my question is why more people don't do this then.
Not sure if this has been asked before, but I haven't seen it.
Chart I'm using for my MHash/s numbers: https://en.bitcoin.it/wiki/Mining_hardware_comparison
Calculator: http://dev.bitcoinx.com/profit/
submitted by bobbob1016 to Bitcoin [link] [comments]

r/Bitcoin. log in sign up. User account menu. 2. Can't seem to mine with GPU. Close. 2. Posted by. u/ryanmm. 8 years ago. Archived. Can't seem to mine with GPU. I've recently been trying to use GUIminer to mine with my GPU. I am just using a fairly old work PC, but it just sits in an office for most of the day and figured I could put it to good use. The machine is a 2.9 ghz Quad core with a ... Im Allgemeinen ist die ATI 6990 (758 MH/s) ist am schnellsten, aber es verbraucht ziemlich wenig Energie. Die ATI 5970 (655 MH/s) läuft bei 86% der Geschwindigkeit einer 6990, aber verbraucht weniger Strom. Wenn Sie haben eine begrenzte Anzahl von slots auf dem motherboard mit günstigen Strom, wählen Sie die ATI 6990. Wenn man unbegrenzt PCI-E slots und relativ teuren Strom, wählen Sie die ... PDF After its introduction in 2008, increasing Bitcoin prices and a booming number of other cryptocurrencies lead to a growing discussion of how much... Find, read and cite all the research ... My computer currently gets like 20MHash/s. I am debating whether or not to get an ATI 6990 because it supposedly gets 700, which with my rough... 28 Apr 2012 - Kinlo Pool Chart; 19 Apr 2012 - Video - Bitcoin Mining Rig Extraordinaire; 08 Apr 2012 - BitForce Sha256 Mini Rig; 27 Mar 2012 - GPU Mining Dead; 25 Mar 2012 - Drilled Gold Bar Tungsten; 11 Mar 2012 - FPGA Game Changer; 11 Mar 2012 - Bitcoin Miner Estimate; 22 Feb 2012 - Eighty Percent Milestone; 21 Feb 2012 - The Garage Miner; 19 Feb 2012 - Multi Rig Sale February 2012; 02 Feb ...

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