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Litecoin Confirmations

Litecoin transactions are recorded in the Litecoin blockchain (a ledger held by most clients). A new block is added to the blockchain roughly every 2.5 minutes (whenever a small enough hash value is found for the proof-of-work scheme). A transaction is usually considered complete after six blocks, or 15 minutes, though for smaller transactions, fewer than six blocks may be needed for adequate security.Litecoin uses scrypt for its proof of work algorithm, and SHA-256d as a subroutine. Bitcoin exclusively uses SHA-256d for its hash function.

The scrypt hash function used by Litecoin depends on fast access to large amounts of memory per hash attempt, rather than depending just on fast arithmetic operations. By using the input as a seed to fill a large amount of memory with a pseudorandom sequence, and then using another seed derived from the input in order to access this sequence at pseudorandom points while generating the output hash, the difficulty to run many instances of scrypt in parallel by using the ALUs of a modern graphics card increases greatly, compared to Bitcoin's GPU-friendly SHA-256 algorithm.

Since memory is the resource of general-purpose computers which is the most expensive to reproduce for ASICs, in particular it's more expensive than ALUs, this means that a one-time investment in ASICs for Litecoin mining would be much more expensive. The memory size parameter of scrypt was selected (originally by ArtForz and Lolcust) to fit into 128.5kB, so that it'd only hit the L1/L2 cache and leave the L3 cache and the RAM alone. This means that it's possible to mine Litecoin without affecting system responsiveness, while still requiring a significantly large amount of memory per hash attempt, and without affecting the GPU's hashing speed if the GPU is already used to mine Litecoin or Bitcoin.

The scrypt parameters that Litecoin uses (N=1024, p=1, r=1) let users who run the Litecoin client--and therefore need to verify the blocks--multitask in their operating system without affecting the responsiveness. This still reduces the advantage of ASIC by a 10-fold estimate, according to Colin Percival, the creator of scrypt.

Since modern graphics cards have plenty of RAM, they do prove useful for Litecoin mining. You can also see the difference in mining difficulty by viewing Litecoin's mining hardware comparison and comparing it to Bitcoin's comparison page. Where a common GPU will mine Bitcoin in MH/s (megahashes), Litecoin is mined in kH/s (kilohashes).

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