I have found a similar question with an answer updated in July 2016.
http://bitcoin.stackexchange.com/questions/11170/why-is-pruning-not-considered-already-at-the-moment

Thanks.
I am going to investigate further on the "pruning feature".

Sorry to hijack your thread OP, but I want to add a question here. In my limited knowledge of pruning I suspect that if EVERYONE runs a pruned

version of the software, then those old tx's are lost forever? I have a basic understanding of Pruning, and I have not taken the time to brush up

on the research... so I am asking this out of pure laziness to do the research myself. 

I think it is very interstning that satoshi has some code in there not being active.
So to sum this up: the diskspace is currently not checked on the core github source? Or did i understand it wrong?

With an UTXO commitment in the block header it would not be necessary to always download the complete blockchain to bootstrap a new node.

It's enough to verify the blockchain once. If you need to bootstrap another node, you could start with the last verified block (hash) and the corresponding set of unspent outputs (hash).

The idea is to store an UTXO hash in the block header. If nodes or any other source provides an UTXO set for download, I can bootstrap from the last verified block (user provided checkpoint). This should be safe as long as there is no easy way to create hash collisions.

You need a matching UTXO set for every block you want to start with. Practically it might be enough to have an UTXO snapshot every month or every year.

The identification of the correct chain is easy. Only the correct block header chain will lead to the already validated block hash. A different chain will lead to a different block hash unless there is a collision.

No. You can enable pruning at any time and it will reduce the amount of space used on disk to a few GB at most. You do not, at any point in time, need to have the full blockchain on disk.

That is correct.

No. Pruning is working exactly as intended. Pruning and what Satoshi said in the whitepaper are two completely different things.

Because without the full transaction history, that data can be forged. You can't know whether a UTXO is legitimate without knowing the transaction that created it and what that transaction spent. You need the full transaction history to verify the validity of a UTXO. With UTXO commitments (which do not yet exist) we could do that, but we will need a fork to enable such functionality.

You can do that locally once you have downloaded and verified the blockchain. You cannot do that to the blockchain as a whole because I don't know whether the transaction "Bob->Charlie (25BTC)" is actually legitimate when I am syncing a new node. For me to check that it is legit, I need to know where Bob got the output to spend. Just because a transaction is in a block with a valid proof of work does not automatically mean that all transactions in the block are valid; that's not how Bitcoin works.

You can certainly do this locally as that is basically what Satoshi suggests in the whitepaper. But as gmaxwell pointed out above, what we do now for pruning locally is way more efficient than what Satoshi suggests. Satoshi suggests that we throw away parts of blocks as UTXOs are spent. But what we do is that we maintain a separate database with our UTXOs and chainstate data so we don't actually need to have the blocks themselves. So we just throw away old blocks entirely because we have validated them and taken the things from them that we need and stored them elsewhere in a more compact form.