Suggest suitable basic data types

IGCSE Computer Science – Full Syllabus Notes (0478)

This document covers every topic required for the Cambridge IGCSE Computer Science (0478) examination. It is written to the assessment objectives (AO1‑AO3) and includes concise definitions, tables for quick reference, worked examples and exam‑style questions.

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1. Data Representation (Topic 1)

1.1 Number systems

• Binary (base‑2) – digits 0 and 1. 1 byte = 8 bits.
• Octal (base‑8) – digits 0‑7. 3 binary bits = 1 octal digit.
• Hexadecimal (base‑16) – digits 0‑9 and A‑F. 4 binary bits = 1 hex digit.

Binary	Octal	Hexadecimal	Decimal
0000 0001	001	01	1
0000 1010	012	0A	10
1111 1111	377	FF	255

1.2 Conversions (AO1)

1. Binary → Decimal: multiply each bit by 2ⁿ and sum.
2. Decimal → Binary: repeatedly divide by 2, record remainders.
3. Binary ↔ Hex: group bits in fours.
4. Binary ↔ Octal: group bits in threes.

1.3 Two’s‑complement (AO2)

• Used for signed integers.
• Positive numbers = ordinary binary.
• Negative number = invert bits + 1.

Example: Represent –18 in 8‑bit two’s‑complement.

18  = 0001 0010
invert = 1110 1101
+1    = 1110 1110  → –18

1.4 Overflow & logical shifts (AO2)

• Overflow occurs when the result needs more bits than the storage size.
• Logical shift left (LSL) – inserts 0 on the right, multiplies by 2.
• Logical shift right (LSR) – discards right‑most bit, divides by 2 (unsigned).

1.5 Practice questions

1. Convert 101101₂ to hexadecimal.
2. What is the decimal value of 1111 1110₂ in two’s‑complement (8‑bit)?
3. Shift 0010 1101₂ left by two positions. What is the new binary value and its decimal equivalent?

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2. Text, Sound & Images (Topic 2)

2.1 Text representation

• ASCII – 7‑bit code, 128 characters (e.g., ‘A’ = 65₁₀ = 0100 0001₂).
• Unicode (UTF‑8) – variable‑length, can represent > 1 million characters.

2.2 Sound representation

Parameter	Typical value	Effect on file size
Sample rate	44 kHz (CD quality)	Higher rate → more samples per second → larger file.
Bit depth	16 bits (CD) or 24 bits (studio)	More bits per sample → greater dynamic range, larger file.
Channels	Mono (1) or Stereo (2)	Stereo doubles the data.

File‑size formula (uncompressed):

Size (bits) = SampleRate × BitDepth × Channels × Duration (seconds)

2.3 Image representation

Attribute	Typical values
Resolution	e.g., 1920 × 1080 pixels (Full HD)
Colour depth	24‑bit (True colour = 16 777 216 colours)
Pixel size	Colour depth ÷ 8 bytes per pixel (e.g., 24‑bit = 3 bytes)

Uncompressed bitmap size:

Size (bytes) = Width × Height × (ColourDepth ÷ 8)

2.4 Mini‑quiz

1. Calculate the size of a 5‑second mono audio clip recorded at 44 kHz, 16‑bit depth.
2. How many bytes are required for a 800 × 600 pixel image with 24‑bit colour?
3. What decimal value does the ASCII code 0x41 represent?

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3. Data Storage & Compression (Topic 3)

3.1 Storage units (AO1)

Unit	Symbol	Bytes
bit	b	1/8 byte
byte	B	1
kilobyte	KB	10³ B
kibibyte	KiB	2¹⁰ B
megabyte	MB	10⁶ B
mebibyte	MiB	2²⁰ B
gigabyte	GB	10⁹ B
gibibyte	GiB	2³⁰ B
exbibyte	EiB	2⁶⁰ B

3.2 Lossless vs. lossy compression (AO2)

• Lossless – original data can be perfectly reconstructed (e.g., ZIP, PNG, FLAC).
• Lossy – some data is discarded to achieve higher compression (e.g., MP3, JPEG, MPEG‑4).

3.3 Simple Run‑Length Encoding (RLE) example

Original bitmap row: 1111111100000011
RLE (value, count): (1,8)(0,6)(1,2)
Compressed size = 2 bytes per pair → 6 bytes vs. 16 bytes original.

3.4 Impact on bandwidth (AO3)

Compressed data travels faster because fewer bits are transmitted. Example: a 5 MB video compressed to 500 KB reduces transmission time by a factor of 10 on a 1 Mbps link.

3.5 Exercise

Compress the binary string 0001111000 using RLE and state the compression ratio.

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4. Data Transmission (Topic 4)

4.1 Packet structure

• Header – source/destination addresses, protocol, length.
• Payload – the actual data being sent.
• Trailer – error‑checking information (e.g., CRC).

4.2 Error detection (AO2)

Method	How it works	Typical use
Parity bit (even/odd)	Count 1‑bits; add a bit to make total even (or odd).	Simple serial links, early Ethernet.
Checksum	Sum of all bytes modulo 2⁸ (or 2¹⁶); receiver recomputes and compares.	IP, TCP/UDP.
CRC (Cyclic Redundancy Check)	Polynomial division; highly reliable.	Ethernet, USB.

4.3 Automatic Repeat Request (ARQ) (AO2)

• Sender transmits a packet and waits for an ACK (acknowledgement).
• If NACK or timeout occurs, the packet is retransmitted.

4.4 Common transmission media (AO1)

Medium	Typical speed	Key characteristic
Twisted‑pair (UTP)	10 Mbps – 1 Gbps	Widely used for LANs.
Fiber‑optic	10 Gbps – 100 Gbps	Low attenuation, immune to EMI.
Wi‑Fi (IEEE 802.11)	11 Mbps – 600 Mbps	Wireless LAN, uses radio frequencies.
Bluetooth	1 Mbps – 3 Mbps	Short‑range, low power.

4.5 Encryption (concept only – no maths) (AO3)

• Symmetric key – same secret key for encryption and decryption (e.g., AES).
• Asymmetric (public‑key) – pair of keys; public key encrypts, private key decrypts (e.g., RSA). Used for secure email and HTTPS.

4.6 Sample question

Explain why a parity bit can detect an odd number of bit errors but not an even number.

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5. Computer Hardware (Topic 5)

5.1 CPU components & the Fetch‑Decode‑Execute (FDE) cycle (AO1‑AO2)

1. Fetch – instruction is read from memory into the Instruction Register (IR).
2. Decode – Control Unit interprets the opcode and determines required operands.
3. Execute – ALU performs the operation; result may be stored in a register or memory.

5.2 Cores and cache (AO2)

• Multi‑core CPUs can execute several instruction streams simultaneously, improving performance.
• Cache (L1, L2, L3) stores frequently accessed data close to the CPU, reducing memory‑access time.

5.3 Instruction set (AO1)

• Set of binary codes that the CPU can execute (e.g., ADD, SUB, LOAD, STORE, JUMP).
• RISC vs. CISC – not examined in depth, but know that “RISC = Reduced Instruction Set Computer”.

5.4 Embedded systems (AO3)

Device	Typical CPU	Purpose
Digital thermostat	8‑bit microcontroller	Control heating/cooling.
Smartphone	ARM multi‑core	General‑purpose computing, sensors.
Microwave oven	16‑bit microcontroller	Timer and power control.

5.5 Quick check

1. Name the three stages of the FDE cycle.
2. Why does a larger cache improve performance?
3. Give one example of an embedded system and the problem it solves.

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6. Input/Output Devices & Storage (Topic 6)

6.1 Primary vs. secondary storage (AO1)

• Primary (volatile) – RAM, registers. Data lost when power is removed.
• Secondary (non‑volatile) – Hard‑disk, SSD, optical disc, magnetic tape. Retains data without power.

6.2 Types of secondary storage (AO2)

Technology	Typical speed	Typical capacity	Key advantage
Magnetic HDD	80‑200 MB/s	500 GB‑4 TB	Low cost per GB.
Solid‑State Drive (SSD)	300‑3500 MB/s	256 GB‑2 TB	No moving parts → faster, more reliable.
Optical (CD/DVD/Blu‑ray)	1‑10 MB/s	700 MB‑50 GB	Portable, cheap for distribution.
Magnetic tape	100‑300 MB/s (sequential)	10 TB‑100 TB	Excellent for backup archives.

6.3 Virtual memory (AO2)

• Allows programs to use more memory than physically available by swapping pages to secondary storage.
• Page‑fault occurs when required data is not in RAM; OS loads it from disk.

6.4 Cloud storage (AO3)

• Data stored on remote servers accessed via the Internet.
• Pros: accessibility, automatic backup, scalability.
• Cons: dependence on network, possible security/privacy issues.

6.5 Sample question

Compare a magnetic hard‑disk and an SSD in terms of speed, durability and cost.

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7. Network Hardware (Topic 7)

7.1 Key devices (AO1)

Device	Function	Typical address type
Network Interface Card (NIC)	Connects a computer to a network.	MAC address (48‑bit)
Router	Forwards packets between different networks; performs IP routing.	IP address (IPv4/IPv6)
Switch	Connects multiple devices within the same LAN; forwards frames based on MAC.	MAC address
Hub	Simple repeat‑and‑broadcast device; no address filtering.	None (broadcast only)
Wireless Access Point (WAP)	Provides Wi‑Fi connectivity to wired LAN.	MAC address

7.2 Addressing basics (AO2)

• MAC address – 48‑bit hardware identifier, written as six hex pairs (e.g., 00:1A:2B:3C:4D:5E).
• IP address (IPv4) – 32‑bit dotted decimal (e.g., 192.168.1.10). Subnet mask determines network vs. host portion.

7.3 Example scenario (AO3)

A school network uses a router (192.168.0.1) to connect to the Internet, a switch to link 20 computers, and a WAP for tablets. Explain how a tablet obtains an IP address and reaches a website.

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8. Databases – Choosing Suitable Basic Data Types (Topic 9)

8.1 Formal definitions of the most common SQL data types

SQL data type	Definition (syllabus wording)	Typical range / size	SQL example (field definition)
INTEGER	Whole numbers without a decimal part.	‑2 147 483 648 to 2 147 483 647 (32‑bit signed)	StudentID INTEGER PRIMARY KEY AUTOINCREMENT
SMALLINT	Whole numbers that need a smaller range.	‑32 768 to 32 767 (16‑bit signed)	Age SMALLINT
REAL / FLOAT	Numbers that may contain a fractional part.	≈ ±3.4 × 10³⁸ with ~7 decimal digits of precision	Weight REAL
DECIMAL(p,s)	Exact numeric values with p total digits, s after the decimal point (used for money).	Range depends on p; two‑decimal‑place precision when DECIMAL(10,2)	EnrolmentFee DECIMAL(10,2)
CHAR(n)	Fixed‑length character string of exactly n characters.	n ≤ 255 (each character 1 byte)	Gender CHAR(1)
VARCHAR(n)	Variable‑length character string up to n characters.	n ≤ 65535 (stores only the characters entered + 1 byte length)	FirstName VARCHAR(30)
BOOLEAN	Two possible values – TRUE / FALSE (or 1/0).	1 byte (implementation dependent)	IsFullTime BOOLEAN
DATE	Calendar date (year‑month‑day).	‘YYYY‑MM‑DD’ – stored in 3 bytes on most systems.	DateOfBirth DATE
TIME	Clock time (hour‑minute‑second).	‘HH:MM:SS’ – stored in 3 bytes.	StartTime TIME
TIMESTAMP	Combined date and time (e.g., ‘2025‑12‑30 14:23:05’).	Usually 8 bytes.	RegistrationDate TIMESTAMP

8.2 Guidelines for selecting the most suitable data type (AO2)

1. Use the smallest type that can hold every possible value – saves storage and speeds up searching.
2. Choose numeric types for fields that will be used in calculations (e.g., totals, averages).
3. Prefer CHAR(n) only when every entry is exactly n characters (e.g., country codes). Otherwise use VARCHAR(n).
4. Store dates and times with the dedicated DATE, TIME or TIMESTAMP types – this enables date arithmetic and proper sorting.
5. Use BOOLEAN for binary choices; avoid “yes/no” as text.
6. Anticipate future growth – give a slightly larger VARCHAR limit if the field may need more characters later.
7. Primary keys should be unique, non‑null, never change – an auto‑increment INTEGER is ideal.
8. Foreign‑key fields must have the same data type as the primary key they reference.

8.3 Primary key, foreign key and field validation (AO3)

• Primary key (PK) – uniquely identifies each record. Declared with PRIMARY KEY in the CREATE TABLE statement.
• Foreign key (FK) – creates a link to another table’s PK. Declared with REFERENCES other_table(other_field) and must match the PK’s data type.
• Field validation – enforce sensible data at entry:
  • CHECK constraints (e.g., CHECK (Age >= 0)).
  • NOT NULL for mandatory fields.
  • Length limits via CHAR/VARCHAR.

8.4 Worked example – Student table (AO1‑AO3)

CREATE TABLE Student (
    StudentID      INTEGER PRIMARY KEY AUTOINCREMENT,
    FirstName      VARCHAR(30) NOT NULL,
    LastName       VARCHAR(30) NOT NULL,
    DateOfBirth    DATE NOT NULL,
    Gender         CHAR(1) CHECK (Gender IN ('M','F','O')),
    Age            SMALLINT CHECK (Age >= 0),
    EnrolmentFee   DECIMAL(10,2) NOT NULL,
    IsFullTime     BOOLEAN NOT NULL,
    RegistrationDate TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

Field	Suggested data type	Reasoning (syllabus points)
StudentID	INTEGER (auto‑increment, PK)	Unique whole‑number identifier; smallest suitable integer type.
FirstName / LastName	VARCHAR(30)	Variable‑length text; 30 characters is enough for typical names.
DateOfBirth	DATE	Allows age calculations and proper sorting.
Gender	CHAR(1)	Only one character needed; fixed length saves space.
Age	SMALLINT	Student ages never exceed 150 – SMALLINT is sufficient.
EnrolmentFee	DECIMAL(10,2)	Exact monetary value; two decimal places avoid rounding errors.
IsFullTime	BOOLEAN	Binary choice – true if full‑time, false otherwise.
RegistrationDate	TIMESTAMP	Records both date and time of registration automatically.

8.5 Common SQL statements (AO1)

• SELECT – retrieve data
  SELECT FirstName, LastName FROM Student WHERE IsFullTime = TRUE;
• INSERT – add a record
  INSERT INTO Student (FirstName, LastName, DateOfBirth, Gender, Age, EnrolmentFee, IsFullTime) VALUES ('Ada', 'Lovelace', '2000-12-10', 'F', 23, 1500.00, TRUE);
• UPDATE – modify data
  UPDATE Student SET EnrolmentFee = EnrolmentFee * 1.05 WHERE Age >= 18;
• DELETE – remove records
  DELETE FROM Student WHERE IsFullTime = FALSE AND Age < 18;
• ORDER BY – sort results
  SELECT FirstName, EnrolmentFee FROM Student ORDER BY EnrolmentFee DESC LIMIT 5;
• Aggregates – COUNT, SUM, AVG, MIN, MAX
  SELECT AVG(EnrolmentFee) FROM Student WHERE IsFullTime = TRUE;
• GROUP BY – group rows for aggregation
  SELECT Gender, COUNT(*) FROM Student GROUP BY Gender;

8.6 Exam‑style practice (AO3)

1. Identify the most appropriate data type for each field and write the full CREATE TABLE line:

   Field	Typical content
   PhoneNumber	e.g. 07123456789
   Score	0 – 100 (integer)
   Comment	Free‑text up to 200 characters
   Joined	date and time of first login

2. Write an SQL query that lists the three students with the highest EnrolmentFee, showing their full name (concatenated) and fee, ordered from highest to lowest.
3. Explain why DECIMAL(10,2) is preferred to REAL for storing monetary values.
4. A table Course has primary key CourseID INTEGER. Write the field definition for a foreign key CourseID in the StudentCourse table.
5. Calculate the storage required (in bytes) for a table that contains 1 000 records with the fields: StudentID INTEGER, Age SMALLINT, IsFullTime BOOLEAN. (Assume 4 bytes for INTEGER, 2 bytes for SMALLINT, 1 byte for BOOLEAN.)

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9. Quick Reference Sheet (exam cheat‑sheet)

Data type	Typical use	Size (bytes)
INTEGER	IDs, counts	4
SMALLINT	Small whole numbers (age)	2
REAL / FLOAT	Measurements, scientific data	4‑8 (implementation)
DECIMAL(p,s)	Money, exact fixed‑point	Varies Create an account or Login to take a Quiz 41 views 0 improvement suggestions Log in to suggest improvements to this note. Support e-Consult Kenya Your generous donation helps us continue providing free Cambridge IGCSE & A-Level resources, past papers, syllabus notes, revision questions, and high-quality online tutoring to students across Kenya. Powered by