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After much tweaking, I've finally managed to find that

--temp-target 78 --gpu-fan 33-100

are the best flags for me on cgminer for BTC or any SHA-256 based coin for that matter, but for LTC (or any other scrypt altcoin) it completely fails. I get 190 Mh/s when mining for BTC, which is right on the mark according to the mining hardware comparison chart, but when it comes to scrypt, I only get 1/10 of what the chart said I should get (I'm getting 20Kh/s). I tried using the flags on LTC's chart too and also had no effect. Any light on this anyone?

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scrypt hashes are harder than sha256 hashes. –  Nick ODell Jun 24 '13 at 3:10
What chart are you talking about? –  David Schwartz Jun 24 '13 at 7:17
Yes, but they should match the chart as they do for BTC. Charts: github.com/litecoin-project/litecoin/wiki/… and en.bitcoin.it/wiki/Mining_hardware_comparison –  Tom Jun 24 '13 at 13:26
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1 Answer

Tom, Let me provide you with a real answer instead of a one liner...

BitCoin and LiteCoin run on two different types of encryption. BitCoin runs on what is called SHA-256 encryption. SHA-256 the first three characters (SHA) stand for "Secure Hash Algorithm", the last three characters (256) stands for the number of output bits (256 bits). SHA-256 was "designed by the U.S. National Security Agency (NSA) and published in 2001 by the NIST as a U.S. Federal Information Processing Standard." (Wikipedia, SHA-2)

Litecoin runs on a lesser known, and much newer algorythm called scrypt.

"The scrypt function is specifically designed to hinder such [hacking] attempts by raising the resource demands of the algorithm. Specifically, the algorithm is designed to use a large amount of memory compared to other password-based KDFs, making the size and the cost of a hardware implementation much more expensive, and therefore limiting the amount of parallelism an attacker can use (for a given amount of financial resources)" (Wikipedia, scrypt)

After reading the description of the two algorithms we find out that scrypt is designed to be slow whereas SHA-256 is meant to be faster.

On a side note, The creator of litecoin thought scrypt would impede large mining farms from controlling the network, allowing a more decentralized network. The creator also hoped to give equality to all users as they only had the ability to CPU mine at the beginning of litecoin's history. It was not until SolidCoin (referred in the bitcoin community as scamcoin) tried to compete with litecoin that a GPU based scrypt miner came out, Reaper. This emerging of Reaper was due to the main developer of solidcoin trying to discredit litecoin's abilities as an implementation of a decentralized currency.(Source. Myself, I lived through it). I believe that Reaper first came out in September of 2011.

References: https://en.wikipedia.org/wiki/SHA-2 (Retrieved 6/23/13@2345 EDT) http://en.wikipedia.org/wiki/Scrypt (Retrieved 6/23/13@2345 EDT) http://csrc.nist.gov/groups/ST/toolkit/secure_hashing.html#Approved%20Algorithms (Retrieved 6/23/13@2345 EDT)

as always, i may be wrong with information, if you do see errors, please let me know so i can fix it. Thanks!

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Tom, my Name is Joe not jimmy. You are looking at the optimal performance level of the machine. As i discussed you are not going to get the exact rate that others do. Scrypt uses memory intensive processing. If you do not have as much computer RAM as you do RAM on your video card you will not be able to mine fast. I thought it was obvious by the post that you are not going to get the optimal speed with an emerging technology, but it apparently was not and so i apologize :( But please, if you are going to get in to any bitcoin or alt coin, read everything about it. Let me know if i answered it. –  Joe White Jun 24 '13 at 17:07
sorry, not really. The numbers for LTC should be around 1000x smaller, but for me they are actually 10000x smaller, the numbers should match the charts but they don't, at least not on LTC. I don't know if it's because I've only got 2GB DDR2 or bc I'm running Win 32 bits (which I don't know if it makes any difference), but it isn't the case that my system has less RAM memory than the card bc the 6770 has actually only 1GB of memory. Thanks :) –  Tom Jun 25 '13 at 17:30
hey tom, try doing some "tweaking" of your gpus then... try increasing the intensity... for strong hashing i use 16-18, if you want to use your computer while hashing i go with 12, if you want no lag while hashing, go with 0. if you really want to play games but hash anyway, set it to something like -1. –  Joe White Jun 25 '13 at 17:32
13 renders my computers unusable and hashrate starts to decline. I had heard an explanation for it that is tied to your thread concurrency. The aggression should never go beyond the number 2^x where x gives the result closest to your thread concurrency. TC for a 6770 is 3200 so 12 is the sweet spot for me since 2^12 = 4096. I don't know if that's true or not but it certainly is the sweet spot for me –  Tom Jun 25 '13 at 20:39
alright, so you got it down then? Cool. Stay around keep on posting –  Joe White Jun 25 '13 at 21:27
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