Crypto currency is a digital currency whose value is decided by the popularity of that type of currency. Most popular is Bitcoin.
This is how a Bitcoin transaction occurs.
Frst we need to initiate a transaction, this is done by using a Bitcoin wallet or the I'd used in Bitcoin. When the transaction is initiated we need to verify some things like
1) Does the porson owe the id and how much is the balance.
2) Is this transaction valid.
For this, a large mathematical calculation is given to all miners or mining pool, 1st miner or pool to be successful in solving the problem will be given the lotry of verifying this transaction.
When this traction is verified, Bitcoin transfer takes place and some part of Bitcoin is given to miner as a reward.
Miner has very huge importance in Bitcoin mining, each miner has to keep the record of all the traction ever taken place in Bitcoin history and this mathematical calculation given to a miner is very complex and the complexity depends on the overall strength of all miners. This is to keep this transaction genuine and keep this lotry system working.
People started mining using CPU but after sometime people developed software which could use GPU. These complex calculations are not dependent on each other, this lead to the conclusion that we could use independent cores to mine and this is what we have in abundance with GPU.
So simplified....
1) Crypto currency is the real digital representation of normal currency. And its value can increase or decrease.
2)Calculation given to stress test the miner( a pool of hardware or a single person with a single or more hardware) is not dependant on each other for eg 2+4+9+5=20
We can do it with a single core and we will do 2+4+9+5 then 2+4+14 then 2+18 then 20
Or we can use 2+4+9+5 then 6+14 then 20
Here core 1 did 2+4 and core 2 did 9+5 then after those are done another core does the sum of output of both cores. As u can logically think this is faster. Thus we use GPU or specific devices which are designed to parrellel task.
If you want to know these calculations are finding prime numbers which make up a number like a system willl be given 143. Computer has to find 11*13=143 11 and 13 is the key. Like this a number like 676788377773737377377 will be given and it will be quite hard to find the number.
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I hope this clears your doubt..
I'm using my phone to type so there will be typing mistakes.