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:
submitted by bobbob1016 to Bitcoin [link] [comments]

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 ... Bitcoin networking started in 2009 with its unique currency Bitcoin or BTC. The Bitcoin network is a peer-to-peer, distributed network. In this network, all nodes are treated as equal peers. The process of making Bitcoins is called mining, and the participants are called miners. All transactions are carried out and stored in a distributed ledger: the blockchain. The historic transaction data ... NVidia GeForce GPU cards are surprisingly slow in comparison to AMD ATI Radeon HD. It's pointless to run bitcoin mining on NVidia cards. Here list of most effective cards to run mining: Best performance/cost ratio have ATI/AMD Radeon HD 5xxx series cards: Radeon HD 5750 ~140 MHash/s - 90W Radeon HD 5770 ~190 MHash/s - 110W Radeon HD 5830 ~260 MHash/s - 175W Radeon HD 5850 ~290 MHash/s - 151W ... of the ATI Radeon HD 6990 in March 2011 and Canaan’s Avalon1 3 Module in January 2013, efficiency improved from 510,000 W/TH to 8,333 W/TH. Efficiency: GPU and FPGA vs. ASIC miners (Bitcoin mining) (Source: Elwood research) Y ou ra t en i s dw hc l“I mp f” .©E AM gLP v Page 4 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 ...

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