What is Blockchain?
Blockchain is a record structure where transactions are kept in linked blocks and validated by participants through shared rules.
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What problem does blockchain solve?
Blockchain is a data structure where records are maintained in interconnected blocks. In cryptocurrency networks, a primary goal is to determine which transactions are valid and in what order they occurred without needing a single central record manager. In Turkish, the terms “blokzincir” or “blok zinciri” are used.
Thinking of a digital asset as a file that can be easily copied leads to the problem of the same value being spent to two different people. Payment networks using blockchain attempt to prevent this double-spending by maintaining a valid history through shared rules. To achieve this, it is not enough to simply link blocks together; transactions must be verified, and choices must be made between competing histories.
How are blocks linked?
Each block contains transactions and the information necessary for validation. The hash of the previous block can also be part of this connection. A hash is a digital summary of data generated through a computational method. Even a small change in the data results in a different summary. Thus, any attempt to change a past record is noticed in subsequent connections.
However, it is not accurate to say “the hash changed, therefore it is impossible to change history.” Actual security relates to which changes the network accepts and what an attacker must do to produce an alternative history. Accumulated computational work in Bitcoin and economic collateral plus validator votes in Ethereum are different examples of this process.
Block height indicates a block’s sequence in the chain. Different blocks can temporarily exist at the same height. Therefore, a hash is used to uniquely identify a block. Height only describes position; it is not always a unique identity on its own.
What happens when a transaction is sent?
A user specifies the recipient, the amount, and other required fields from their wallet. The wallet signs the transaction with the appropriate key. Nodes check the signature and the spendability of the balance. A valid transaction can then be included in a block. The propagation of a transaction to the network and its inclusion in a block are different stages.
In a transfer example, if Ayşe tries to send the same balance to both Mehmet and Zeynep, both expenditures cannot be included in the valid history. The network determines which one spent the available balance based on the accepted transaction order. The subsequent conflicting transaction is rejected. In this way, copyable digital information is separated from the limited right to spend.
Trading on an exchange does not always create an on-chain transaction. A platform may change balances between its own customers in its internal records. On-chain transactions usually appear during deposits or withdrawals. For this reason, searching for a record in a blockchain explorer for every movement on an exchange screen may not yield results.
Nodes, miners, and validators
A node is a computer running the network software. A full node validates transactions and blocks according to its own rules. A miner performs computations to find blocks in a Proof of Work network. A validator, in structures like Proof of Stake, can participate in proposing blocks and voting. These roles are not identical.
In Bitcoin, running an ordinary full node does not automatically earn mining rewards. In Ethereum, a node being online does not mean it is a staking validator. Tasks that earn rewards may have additional requirements for collateral, hardware, or continuous uptime.
Evaluating network security solely by the number of computers is insufficient. The independence of participants, software diversity, the possibility of transaction censorship, and governance powers are important. The same organization running a thousand servers does not mean there are a thousand independent decision-makers.
Difference between public and permissioned blockchains
In public (open) networks, participation rules apply to everyone, and users can join the network for specific tasks without central permission. In permissioned networks, the authority to write records or validate may be limited to selected institutions. The purpose of use and security assumptions for these two models differ.
A company saying it uses blockchain does not mean the system is open or decentralized like Bitcoin. One should ask which institutions can change records and whether users can perform independent verification. In some applications, the goal is to maintain an audit trail between known institutions; this is not the same as establishing an open crypto network.
What do smart contracts add?
Smart contracts are programs that run on the blockchain according to set rules. Beyond simple transfers, they enable operations like swaps, collateralized debt, or voting. When a user calls a contract, the code executes, and the state of the network may change. Transaction fees are paid for computational resources.
The fact that code executes automatically does not mean it is error-free. Incorrect calculations or the abuse of administrative privileges can lead to losses. Additionally, data transmission systems called oracles may be required for real-world data. A blockchain does not transform an incorrectly received price into accurate information just because it was written to the chain.
What does blockchain not guarantee?
The fact that a record is difficult to change does not prove that the person entering the record is telling the truth. For example, if origin information for a physical product is entered incorrectly, the blockchain can hold this incorrect record permanently. The connection between the real object and the digital record must be verified separately.
Furthermore, not every transaction is anonymous. On public networks, address movements are visible to everyone and can be linked to identities. Mistaken transfers are not automatically reversed by a central customer service. There are also design trade-offs between scaling, data storage costs, and privacy.
Therefore, blockchain is not a technology that should replace every database. It must be evaluated whether multiple parties need to agree on a common history, whether trust in a central operator is accepted, and what independent verification provides. The name of the technology alone does not equate to a good product or a good investment.
Why are confirmation and finality separate?
A transaction appearing in a block is not the final stage in every network. In Bitcoin, the probability of reversal decreases as more blocks are added behind it. In some Proof of Stake networks, there is a separate finality stage through validator votes. The rapid acceptance of a Layer 2 interface and the finalization of the transaction on the main network can also be separate. Therefore, when comparing the speed of two networks, specify whether you are measuring the time to first appearance, economic finality, or the time an exchange takes to credit a balance. The same word “completed” can describe different stages on different screens.