There are almost 17 million coins of Bitcoin, but the coins issue continues through the mining. Each mined block creates new coins (12,5 bitcoins per block) as a reward to the miner. The Bitcoin's issue is limited by algorithm, the maximum coins quantity is 21 million. The last Bitcoin will be mined approximately in 2040.

Bitcoin Gold is a fork of Bitcoin. By almost all parameters the Gold repeats the original Bitcoin, with one exception: the SHA-256 hashing algorithm (is used by Bitcoin), that is replaced by Equihash algorithm, which maces mining un-efficient on ASIC devices and allows to extract Bitcoin Gold on standard GPUs.

Bitcoin Cash is one of Bitcoin fork's. it is designed to solve the network bandwidth problem and rapidly rising commissions. The Bitcoin Cash differs by block size (8 MB against 1 MB of original Bitcoin) and by changed system complexity for every 6 blocks, than Bitcoin's 2016.

Noda is a simple net point that exchanges the data with other net points. Masternoda is a specialized net point that has additional functions, full copy of blockchain and is in permanent activity states. Masternoda can control the activity of the pool, having an up-to-date chain of blocks, while the ordinary nodes don't even have the complete copy of the blockchain.

It's an attempt to send two transactions to the blockchain using the same coins. In other words, it's an attempt to spend two times the same funds

In PoW (proof of work) devices solving the mathematical problems using processing capacity, the more capacity has the miner, the more chances to get the block. In PoS there is no need in processing capacity, nods are trying to form the next block, the probability to form the block is proportional to coins quantity owned by certain net point.

With the softfork the rules for blocks forming are changed insignificantly, net points that are working by new rules can interreact net points which doesn't accept the new rules. In case of hardfork, the blocks forming rules are changing fundamentally and requires the software changing. As a result, net points which doesn't accept the new rules can't interreact with net points which are forming the blocks. In effect, the net is divided into two parts and each one forms its' own chain (at certain moment the old blockсhain divided), hence - a new cryptocurrency appears(e.g. Bitcoin and Bitcoin Cash).

The main difference between ICO (Initial Coin Offering) and IPO (Initial Public Offering) is that with the venture investing, the investor most often receive the company's share in form of privileged shares, while during ICO the investor receive the functional tokens, which can be used inside the project or to be freely sold on the exchange. Furthermore, anyone can take part in ICO, while the IPO held for funds and large investors.

First of all, the cryptocurrency is an accounting unit of interaction inside the decentralized system, it can't exist without blockchain. Token is a debt obligation, it can exist outside blockchain. Token can be issued both decentrally and centrally, by individuals and legal entities, while the cryptocurrency emission controlled by software protocol.

Satoshi Nakamoto is the Bitcoin's creator. At this day the Satoshi is not identified and some believe that behind this nickname hides a group of programmers. Satoshi is also a unit of measure that counts 1/100 000 000 of Bitcoin.

1 Bitcoin = 100 000 000 satoshi.

WEI is a fractional part of ETH. 1 ETH = 1 000 000 000 000 000 000 WEI.

It is fixed length row, obtained from the input row of any other length via specific hash function.

Bitcoin used the SHA-256 algorithm.

The Ethereum used the "ethash" algorithm, that consists of SHA3-256 and SHA3-512 algorithms and makes ETH mining more cheaper and faster than Bitcoins mining.

These are the equivalent concepts that define the sequence of numbers and letters generated in a pair with private key that identifies the network user.

The public key acts as the address and the private key as a password, through which the user can confirm the possession of particular cryptocurrency.

The blockchain technology excludes the possibility of double spending since each transaction is checked for correctness, the system determines whether the coin data was in the previous transactions or not.

A smart-contract is a usual contract from real life, only it is not written on the paper, but in the program code. Thus, a smart-contract can not be executed as under its' conditions the machine itself will execute a smart-contract.

ASIC is a special device for mining of Bitcoin, it can't serve for other purposes, while the graphic cards (GPU) are part of modern computers, and are also a means of cryptocurrency mining, e.g. ETH.

The complexity of the network is changing that the block formation time remains unchanged. If the quantity of miners in the network grows, the blocks mining speed also grows, and the time of one block formation is reduced, therefore it is necessary to rise the networks complexity so that the block formation time remains unchanged.

The Bitcoin blocks are formed on the average of every 10 minutes.

The time of Ethereum block forming is 15 seconds.

A hot wallet is always connected to the internet, it allows to manage coins quickly, but it's also a subject of hacker attacks. A cold wallet doesn't have a persistent connection with internet, it is safer for cryptocurrency storage.

An attack of 51% describes the network status, when more than half of all capacities are concentrated in a single pair of hands. Theoretically, in such proportion of the capacity the attackers can try perform a double spending or perform other actions that will harm the network.