Question: Let me introduce my idea.

Given:

* sizeof( Blockchain ) = 16Gb
* Downloading of one avi film 16GB from the pirate bay ( 5mb/s ) = 2-3 hours
* Downloading of bitcoin's blockchain ( 5mb/s ) = 2-3 days
* One day = 6 \* 24 = 144 blocks.
* Drag - cryptography.

Task:

* Accelerate boot of fresh client to the torrent speed. Similar to **Bootstrap**.

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As I can see, downloading of blockchain is the same hard as mining, because there is every time recalculation of hash, comparing, checking of signs, etc...

What if client will only download this 144 blocks for a day and one super block with 144 hashs of the last valid blocks, thereafter only compare current wallet's addresses with addresses in this 144 blocks without any calculation of its hash.

Is there any alt-coin with such accelerator? 

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E.g. this super blocks might be archived into another ultra-block for a month. Than we have similar to sha(sha(text)) cascade shield against bruteforce attack. 

Downloading of blockchain should takes at max the same time as downloading of 16GB avi from the pirate bay. Say, 5mb/s internet channel + p2p / 16 Gb = 2, may be 3 hours ( in the `no peers case` ), but I spent 2 - 3 days, and I see that this is no internet speed reason, it is CPU + harddisk very very hard job.

Answer: 
When a node learns of a transaction, some validity tests are performed and if the transaction is not yet in the blockchain it knows of with the longest height and the transaction also is valid (i.e., not a double spend) then that transaction is added to that node's memory pool.

If a later transaction arrives at a node but is an attempt to double spending of a transaction that is either already in the blockchain with the longest height or is already in the memory pool, then that later transaction is ignored.

A transaction propagates to nearly all miners within seconds, so most miners would immediately reject your later double-spend attempt since they would already know of the earlier transaction.

Blockchain forks happen all the time (i.e., multiple times each day). So it is entirely possible to have conflicts where a transaction is included in a block on one side of the fork but is not yet in the block (or blocks) on the other side of the fork. Eventually one of the several competing blockchain forks will emerge as the longest chain and the transactions in that chain are the ones reflected in the Bitcoin ledger from then on. That's why exchanges wait until three or six confirmations -- as it is technically possible for there to be variations between sides should a fork occur.

Attackers might use this temporary inconsistency in an attempt to defraud by employing a race attack or other approach. This is requisite reading on the topic: <http://en.bitcoin.it/wiki/Double-spending>
It isn't! The only way to be sure that a transaction is permanent (and thus be sure that the recipient will be able to spend the funds he received) is to wait until a reasonable number of confirmations (blocks mined after the block containing the transaction)