← IGCSE Computer Science Paper 1

Blockchain

A digital ledger: a time-stamped series of records, in order, that cannot be altered.

Part of: IGCSE Computer Science 0478 — 5.2 Digital Currency — Module 18

Understanding Blockchain in IGCSE Computer Science Paper 1

What it does: Digital ledger is the part of the definition that tells us blockchain is a ledger held on computers. Records that cannot be altered is the key feature in the syllabus wording of blockchain. A time-stamp stores the date and time a record was created, so the order of events is known. Blockchain is a series of records, and each one is time-stamped.

Common mistakes: A blockchain is a series of records, so it must be a list that can hold many records. A single number cannot. Line 1 should be blockchain = []. Records in a blockchain cannot be altered once they are written. This line changes record 0. It should only read the record, as in print(ledger[0]).

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This module's key terms are also in a printable crossword (Modules 510–519) and word search (Modules 510–546).

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Learning
Duo
Which description matches the basic form of a blockchain in the IGCSE syllabus?
A paper notebook kept by one bank that staff can rub out and rewriteA digital ledger: a time-stamped series of records that cannot be altered
Matches
A blockchain is a paper ledger that anyone can rub out and rewrite
↓
A blockchain is a digital ledger, not a paper one, and its records cannot be altered, so they cannot be rubbed out or rewritten.
Applying
Meanings
Term
blockchain
Meaning
A digital ledger: a time-stamped series of records, in order, that cannot be altered.
Practice
Blockchain is a digital ledger
Testing
Gaps
Blockchain is a digital of records
Check Answer
Spots
1blockchain = 0
2record = {'time': '09:00'}

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Quick Questions

1. Which description matches the basic form of a blockchain in the IGCSE syllabus?
A. A digital ledger: a time-stamped series of records that cannot be altered ✓
B. A paper notebook kept by one bank that staff can rub out and rewrite
The syllabus describes blockchain, in its basic form, as a digital ledger that is a time-stamped series of records that cannot be altered.
2. What is a ledger?
A. A record of transactions ✓
B. A type of coin or note
A ledger is a record of transactions. A blockchain is a digital version of one.
3. Why is a blockchain called a DIGITAL ledger?
A. Its records are written by hand on paper
B. Its records are stored electronically on computers ✓
Digital means stored and processed by computers. A blockchain keeps its ledger records electronically.
4. What does it mean for a blockchain record to be time-stamped?
A. The date and time it was made is stored with it ✓
B. The record can only be read for a short time
A time-stamp stores the date and time a record was created, so the order of events is known.
5. How are the records in a blockchain arranged?
A. In a random pile with no order
B. As a series, one after another in order ✓
A blockchain is a series of records in order. Time-stamps help show which record came first.

Match the Pairs

blockchain → A digital ledger: a time-stamped series of records, in order, that cannot be altered
time-stamp → The date and time a record was made, stored with that record in the blockchain
A blockchain is a ledger that is stored digitally rather than on paper → digital ledger
Once a record is added to a blockchain, nobody can change it → cannot be altered
A blockchain is a paper ledger that anyone can rub out and rewrite → A blockchain is a digital ledger, not a paper one, and its records cannot be altered, so they cannot be rubbed out or rewritten.
A blockchain is a random pile of records with no time or order → A blockchain is a time-stamped series of records kept in order, not a random pile with no time or order.

Key Term

blockchain
A digital ledger: a time-stamped series of records, in order, that cannot be altered.

Fill in the Blanks

1. Blockchain is a digital ledger of records
Hint: Type the word for a book or file that keeps a record of transactions.
2. Each record has a time-stamp (date, time)
Hint: Type the hyphenated term for the date and time a record was made.
3. blockchain ← [R1, R2, R3] FOR EACH r IN blockchain OUTPUT r
Hint: Type the keyword that loops through the records in the series, one after another.
4. canBeAltered ← FALSE
Hint: Type the Boolean value that shows a record cannot be changed once it is stored.
5. Records in a blockchain cannot be altered
Hint: Type the word meaning changed or edited after being saved.

Spot the Error

Question 1
A blockchain = 0
B record = {'time': '09:00'}
C blockchain.append(record)
D print(len(blockchain))
Line A — A blockchain is a series of records, so it must be a list that can hold many records. A single number cannot. Line 1 should be blockchain = [].
Question 2
A ledger = []
B tx = 'Ava pays Liam 5'
C ledger.append(tx)
D ledger[0] = 'Ava pays Liam 50'
Line D — Records in a blockchain cannot be altered once they are written. This line changes record 0. It should only read the record, as in print(ledger[0]).
Question 3
A chain = []
B now = '2025-01-05 09:00'
C rec = {'time': now, 'amt': 5}
D chain.insert(0, rec)
Line D — The records are kept in order, so a new record goes on the end. insert(0, rec) puts it at the start and breaks the order. It should be chain.append(rec).
Question 4
A stamp = 2025-03-01 10:30
B amount = 20
C record = [stamp, amount]
D chain = [record]
Line A — The time-stamp is the date and time of the record, stored as text. Without quotes this is not valid code. It should be stamp = '2025-03-01 10:30'.
Question 5
A chain = ['A>B 5', 'B>C 2']
B chain.append('C>D 1')
C print(chain[3])
D print(len(chain))
Line C — The chain has 3 records in order, numbered 0, 1 and 2. The newest record is chain[2]. chain[3] does not exist and would cause an error.

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