블록과 체인
블록이 연결되는 방식
블록과 체인은(는) CoddyKit의 무료 Web3 & DApp Development Fundamentals 강의입니다. 이것은 4개 중 1번째 강의입니다. 아래에서 전체 강의를 무료로 읽을 수 있으며, 내장 코드 에디터와 24/7 AI 튜터와 함께 브라우저에서 직접 실습할 수 있습니다. 이 강의는 Web3 & DApp Development Fundamentals 학습 경로의 일부이며, 진행 상황이 웹과 CoddyKit 앱에 동기화됩니다. Web3 & DApp Development Fundamentals 강의에는 총 4개의 강의가 포함되어 있습니다.
이 강의의 일부는 아직 번역되지 않았으며 영어로 표시됩니다.
What Is a Block?
A block is the fundamental container in a blockchain. It bundles together a set of validated transactions along with metadata that ties it to the rest of the chain.
Each block has two main parts:
- Header — metadata (timestamp, hashes, nonce)
- Body — the list of transactions
Anatomy of a Block Header
The header is small but powerful. A typical Ethereum-style header includes:
previousHash— hash of the prior blocktimestamp— when the block was createdmerkleRoot— fingerprint of all transactionsnonce— value used in consensus
The header is what gets hashed to identify the block.
block Header {
previousHash: 0x9f1c...a3
timestamp: 1717000000
merkleRoot: 0x4be2...07
nonce: 42891
}How Blocks Link Together
Every block stores the hash of the previous block. This single field is what turns a pile of blocks into a chain.
Because each block points backward, the blocks form an ordered, append-only sequence reaching all the way back to the very first block.
Block 0 (Genesis)
| hash = 0xAAA
v
Block 1 prevHash = 0xAAA hash = 0xBBB
|
v
Block 2 prevHash = 0xBBB hash = 0xCCCThe Genesis Block
The genesis block is the first block in any blockchain. It is special because it has no parent — its previousHash is typically all zeros.
Every other block can be traced back to genesis, which acts as the shared root of trust for the entire network.
Genesis = {
previousHash: 0x0000000000000000
timestamp: 1438269973
transactions: []
}Why the Backward Link Matters
The backward link makes tampering obvious. If someone alters a transaction in an old block, that block's hash changes.
But the next block stored the old hash in its previousHash field, so the link breaks. The mismatch is instantly detectable.
Chains Are Append-Only
Blockchains are append-only data structures. You can add new blocks to the tip, but you cannot insert or delete blocks in the middle without breaking every link that follows.
This property is the foundation of blockchain immutability.
Block Height
Block height is the number of blocks between a given block and the genesis block. Genesis is height 0, the next block is height 1, and so on.
Height gives every block a clear position and lets the network agree on which chain is longest.
height 0 -> Genesis
height 1 -> Block 1
height 2 -> Block 2
...
height N -> latest blockTransactions Inside a Block
The block body holds an ordered list of transactions. Order matters: it determines the final state after the block is applied.
Once a block is finalized, the transactions it contains — and their order — are fixed forever.
Block 12 body:
tx[0]: Alice -> Bob (5 ETH)
tx[1]: Bob -> Carol (2 ETH)
tx[2]: Carol -> Dave (1 ETH)Block Size and Limits
Blocks cannot grow without limit. Each chain sets a cap — Bitcoin uses a byte limit, while Ethereum caps the total gas a block may consume.
These limits keep blocks small enough to propagate quickly across the network.
Identifying a Block by Its Hash
A block's identity is its hash — the output of running its header through a cryptographic hash function.
Change any field in the header and the hash changes completely. That is why hashes act as tamper-evident fingerprints for blocks.
blockHash = sha256(
previousHash + timestamp +
merkleRoot + nonce
)Putting It Together
A blockchain is simply a linked list of blocks where each link is a cryptographic hash of the prior block.
This combination of ordering, hashing, and append-only writes is what makes the chain trustworthy without any central authority.
Quick Check
Test your understanding of how blocks connect.
Recap: Blocks and Chains
You learned that:
- A block has a header (metadata) and a body (transactions)
- Blocks link by storing the previousHash
- The genesis block is the root with no parent
- Chains are append-only, making them immutable
- A block's identity is its hash
Next, we explore how Merkle Trees summarize all transactions efficiently.
자주 묻는 질문
“블록과 체인” 강의는 무료인가요?
네 — “블록과 체인” 전체 내용을 이 웹사이트에서 무료로 읽을 수 있습니다. 인터랙티브하게 실습하려면(내장 코드 에디터와 24/7 AI 튜터), CoddyKit PRO로 업그레이드하면 Web3 & DApp Development Fundamentals 강의 전체를 잠금 해제할 수 있습니다. Web3 & DApp Development Fundamentals 강의에는 총 4개의 강의가 포함되어 있습니다.
“블록과 체인”에서 뭘 배우나요?
블록이 연결되는 방식 브라우저에서 직접 실행하는 실습 코드로 Web3 & DApp Development Fundamentals을(를) 배우며, 24/7 AI 튜터가 강의를 진행하면서 질문에 답변해줍니다.
Web3 & DApp Development Fundamentals을(를) 시작하는 데 경험이 필요한가요?
사전 경험은 필요하지 않습니다. CoddyKit의 Web3 & DApp Development Fundamentals은(는) 초급자부터 고급 학습자까지를 위해 구성되어 있으므로, 여기서 시작하거나 처음부터 시작할 수 있으며 자신의 속도대로 진행할 수 있습니다. 이것은 4개 중 1번째 강의입니다.
“블록과 체인” 강의는 얼마나 걸리나요?
대부분의 CoddyKit 강의는 약 5~10분이 소요됩니다. 각 강의는 간결하고 인터랙티브하여 꾸준한 진행이 가능하며, 웹과 앱에서 중단한 부분부터 바로 시작할 수 있습니다.
이 Web3 & DApp Development Fundamentals 강의에서 코드를 작성하고 실행할 수 있나요?
네. 모든 Web3 & DApp Development Fundamentals 강의에는 내장 코드 에디터가 포함되어 있으므로, 브라우저에서 바로 실제 코드를 작성하고 실행한 후 즉시 AI 피드백을 받을 수 있습니다 — 로컬 설정이 필요 없습니다.