Topic: FPGA mining for fun and profit - page 4. (Read 67194 times)

32x bigger[8x ? didn't saw bigger chips/matrix] FPGA's, made on modern 0.045 waffer[mean working on clocks, lower(cuz arch limitation), but comparable to modern GPU's]can flush GPU's out of business and reinforce bitcoin or ruin it[cuz majority of inviduals can't afford it at 1st time].

Lol, actually I did already see it, since the author announced it on this very forum.

http://forum.bitcoin.org/index.php?topic=9047.0

See your private message.

Thx.

80MH/s for a $600 piece of equipment?  No thanks.
http://www.terasic.com.tw/cgi-bin/page/archive.pl?Language=English&CategoryNo=139&No=502&PartNo=7

Good find nonetheless.

Did anyone see this yet?

https://github.com/progranism/Open-Source-FPGA-Bitcoin-Miner


found it through http://www.bitcoinminer.com/post/5672391181/open-source-fpga-bitcoin-miner-announced

Thoughts? 50MHash/s or 80MH with proper cooling with an DE2-115 Development Kit (this is not a DE2. It has a Cyclone IV EP4CE115.)

Read it again.  It doesn't say anything even remotely resembling what you are claiming it says.

Generating a valid block after the rest of the network has already moved on to the next one is very nearly pointless.  Do you understand what circumstances must be present for someone to replace the existing chain with a side branch of their own?  How many times do you think they could get away with what the network operators would consider to be a very major event before someone notices?

No, he gets it, and you are still a little behind on the curve.  Having control of 51% of the hashing power of the whole network makes it possible to successfully attack the blockchain for a short period of time.  That period of time being one 10 minute interval.  The whitepaper doesn't go into detail about the odds of success of such an attack, other than to show how it's not really possible at all at less than 50%.  Having just over 50% of the network hashing power doesn't really give you very good odds of success past one block, and an attacker intending to deny transactions into the blockchain for longer than one block has to be able to be certain that no blocks can sneak in under him, for if one gets in and the next is built on top of that before he build one to overwrite that one and one on top to secure his false one then it become exponentially more difficult for him to overwrite two blocks back.  In practice, an attacker wishing to keep this up for an extended period of time needs at least double the hashing power of the network because it's like the attacker is trying to wade up river while the honest nodes are wading down river.  And even with double the rest of the network, some blocks are going to slip in and be covered up again anyway.  At which point the attacker has to choose between trying to overwrite two blocks and then write another before a third is made by the network or simply ignore the one that got away and overwrite the last one to take the network back.

You don't get it. If you have more than 50% of the mining power you can just continue searching for a valid block even after somebody else has found one before you. This way you can make sure that you control every block. This is listed in the weaknesses on the Wiki. Yes, you can technically still add transactions, but there's not much point if they'll never get confirmed.

AMD 7000 series round the corner in the next few months, i'm starting think the GPU's are just gonna progress far quicker and faster than than the FPGA can keep up with for cost ratio, i mean the next gen cards are likely to be close to a 1 ghash each, save your money and wait for the 7 series.

Put your soldering irons away your just going to burn yourselves. 

Sorry, you are just completely wrong about this.  Validity of a transaction is not determined by being in a block or not.  A transaction that isn't in a block merely hasn't been accepted (yet).

Say you had 51% of the total mining capacity.

What are the odds of getting the next block, and being able to prevent transactions that you don't approve of for ~10 minutes?  51%
And the odds of getting the block after that and continuing the blockade out to ~20 minutes?  26%
Add if you need ~30 minutes?  13%
40 minutes?  7%
50 minutes?  3%
An hour?  2%
Two hours?  0.031%

Miners can trivially prove their capacity by signing a challenge nonce with the private keys of the coinbase transactions in their found blocks.

It has seemed pretty lumpy the last couple of days ... are there any tools to see if this is outside "normal" variance ?

Yup, I'm aware of both of these things.  Just pointing out that the hashrate has gone from "below the difficulty" to "double the difficulty" in the past several hours.  This may or may not be significant, but it's at least eyebrow-raising.

EDIT:  It looks like it's peaked and dropped down closer to the trendline now, though.

Note that the spike goes in the wrong direction when the FPGA clusters "just went online", and also compare with this historical chart which shows the variance on a longer time scale.

Where can I find some FPGAs in the City Do you mean London uk financial district eg the city ??

Located here and would be quite interested etc. thanks !

NOW there's been a spike.  Big time.

Hrm.

If so they have become really good at turning them on and off at the same time:
http://bitcoin.sipa.be/speed-lin-2k.png

With more than 50% you can just define every transaction that is not in one of your blocks is invalid, by not validating the blocks found by others. There's no need to double spend or counterfeit.

Hmmmm ... that's got me thinking I'm gonna make some enquiries ... I knew a guy who was supplying them into the City a few years (5?) back.

Well they have stock exchanges all over the world...  Melbourne, Singapore and so on. I know a guy that got a free computer once from a stock broking firm that was always upgrading so its possible there's a nice guy out there that would love to us have his old FPGAs