Blocos e cadeias
Como os blocos se conectam
Blocos e cadeias é uma aula grátis de Web3 & DApp Development Fundamentals no CoddyKit. Esta é a aula 1 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de Web3 & DApp Development Fundamentals, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de Web3 & DApp Development Fundamentals inclui 4 aulas no total.
Partes desta aula ainda não foram traduzidas e aparecem em inglês.
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.
Perguntas Frequentes
A aula “Blocos e cadeias” é grátis?
Sim — o texto completo de “Blocos e cadeias” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de Web3 & DApp Development Fundamentals, atualize para CoddyKit PRO. O curso de Web3 & DApp Development Fundamentals inclui 4 aulas no total.
O que vou aprender em “Blocos e cadeias”?
Como os blocos se conectam Você pratica Web3 & DApp Development Fundamentals com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.
Preciso ter experiência prévia para começar Web3 & DApp Development Fundamentals?
Nenhuma experiência prévia é necessária. Web3 & DApp Development Fundamentals no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 1 de 4.
Quanto tempo leva a aula “Blocos e cadeias”?
A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.
Posso escrever e executar código nesta aula de Web3 & DApp Development Fundamentals?
Sim. Cada aula de Web3 & DApp Development Fundamentals inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.
Todas as aulas deste curso
- Blocos e cadeias
- Árvores de Merkle
- Hashing em blockchain
- Registros distribuídos