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The essence is that Bitshares and Steem, or any other Graphene blockchain technology offspring, work clockwise. Just like counting down, 3-2-1, hey presto! There's another block with transactions added. And such a block could be filled with almost 10.000 transactions. The powerfull witness computers take care of that, in realtime. And they do not have to wait for blocks to be filled to the max. Just work clockswise, 3-2-1-block.

Other blockchain types work with larger timegaps, Bitcoin one block every 10 minutes. And it has a limit in the amount of transactions that fit in, about 1700, more or less. Also the block crypto code needs to be calculated, through a proces called mining. And who ever finds the solutions to the crypto puzzel of the block gets some BTC and the transaction fees added as a bonus.

This means that it pays to have blocks filled to the limit. And currently there are so many BTC transactions waiting for a spot to be added to a block that it could take up to a day before it gets through! For this I can stand witness, as two of my BTC transactions, needed to pay bills, are still waiting in line. Now I could have raised the transaction fee but that was already quite steep. As that is happening, people offering higher transaction fees to get their payment into a block.

And then it still takes 6 confirmations, another 6*10 minutes, to get fully acknowledged the transaction went through. Some coins, spinoffs form Bitcoin, do use faster blocktimes, but still based on the same principles.
There is a risk of waiting in line, and Oh do I know right now, pffffff...

Clockwise, like 1-2-3 and scale tenfold beyond current limits

Daniel Larimer, the well known developer of this blockchain magic, once said that when and if needed the Blockchain technology for Steem, Bitshares and so on, could scale even ten fold what they've currently tested. That means 3-2-1-block with 100.000 transactions.

But if you understand that Bitcoin can handle about 3(!) transactions per second, right now, then you know that 3300 transactions per second for Bitshares and their relatives, like Steem, is amazing! And we are only starting. With the obsolete mining out off the code, with HardFork 17, 'witnesses' can even run on smaller hardware. That takes about 5 to 10 Watt in energy. So, Steem is green!

To summerize it

What it all boils down to is the way the different blockchain systems create blocks and what limits that it has build in. And the way Bitshares, Steem and other Graphene blockchain technology offspring work is that creating blocks clockwise at the count of three is the clou.

Otherwise something like this, me posting a reply to you, would take forever. A social media plaform would be extremely slow, like watching paint dry.

Yet, here we are, I click post and 3-2-1, it is in a block, connected to the chain, done so by the witness computers.

Hope I was able to clearify the difference.