Part 01- Operating Systems – Memory representation Techniques Byte Addressable and Word Addressable

Part 01- Operating Systems – Memory representation Techniques Byte Addressable and Word Addressable

Operating Systems – Memory Representation Techniques

Part 01: Byte Addressable & Word Addressable Memory

Memory representation techniques determine how data is stored and accessed in a computer system. The two main types of addressing techniques are Byte Addressable Memory and Word Addressable Memory.

1. Byte Addressable Memory

In a byte-addressable memory system, each individual byte (8 bits) has a unique address. This means that the smallest unit of memory that can be accessed is one byte.

Characteristics:

 Each memory address refers to a single byte (8 bits).
 Common in modern computer architectures (x86, ARM).
 Supports variable-sized data types (1-byte, 2-byte, 4-byte, etc.).

Example:

Assume we have a 32-bit memory system (4 bytes per word).

• Address 1000 stores 1 byte of data.
• Address 1001 stores the next 1 byte, and so on.

Memory Address	Data Stored
1000	10101010
1001	11001100
1002	11110000
1003	00001111

 If we want to fetch a 4-byte integer, the CPU will read four consecutive byte addresses.

2. Word Addressable Memory

In a word-addressable memory system, the smallest unit that can be addressed is a word, which may be 2, 4, or more bytes depending on the architecture.

Characteristics:

 Each memory address refers to a word instead of a byte.
 Mostly found in older architectures (mainframes, embedded systems).
 More efficient for fixed-size data processing.

Example:

Assume a word size of 4 bytes (32-bit word size).

• Address 1000 refers to a whole word (4 bytes).
• Address 1001 does not exist (because each address represents an entire word).

Word Address	Data Stored (4 Bytes)
1000	10101010 11001100 11110000 00001111
1001	Not Available
1002	Not Available
1003	Not Available

 Here, fetching a 4-byte integer requires a single memory access, making it faster for fixed-size operations.

3. Key Differences Between Byte & Word Addressable Memory

Feature	Byte Addressable	Word Addressable
Smallest Addressable Unit	1 Byte (8 bits)	1 Word (2, 4, or more bytes)
Common In	Modern systems (PCs, smartphones)	Older/mainframe systems
Flexibility	Supports different data sizes (1, 2, 4, 8 bytes)	Limited flexibility (fixed word size)
Efficiency	Better for variable data	Faster for fixed-size processing

4. Real-Life Applications

• Byte Addressable Memory: Used in general-purpose computers, laptops, smartphones, where different data types (char, int, float) need efficient storage.
• Word Addressable Memory: Used in high-performance computing, DSPs (Digital Signal Processors), some embedded systems, where fixed-size operations are more efficient.

Conclusion

• Most modern computers use Byte Addressable Memory for flexibility.
• Word Addressable Memory is efficient for specialized applications like high-speed computation.
• Understanding these techniques helps in system design and memory optimization.

Would you like examples of memory addressing calculations or more details on how CPU fetches data?

Part 01- Operating Systems – Memory representation Techniques Byte Addressable and Word Addressable

OPERATING SYSTEM Lecture Notes On

UNIT – I – Operating System – SBS1206

Operating System

Certainly! Here’s a clear and concise explanation of:

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Operating Systems – Part 01: Memory Representation Techniques

Byte Addressable vs Word Addressable Memory

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1. What is Memory Addressing?

Memory addressing refers to how memory locations are identified and accessed. The Operating System (OS) and CPU architecture define how data is stored and retrieved from main memory (RAM).

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2. Byte Addressable Memory

Definition:

In byte-addressable memory, each memory address points to one byte (8 bits) of data.

Example:

If a variable is 4 bytes, and starts at address 1000, it occupies 1000 to 1003.

Common In:

• Most modern computers (e.g., Intel, ARM processors)

• Easy to manipulate individual bytes

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3. Word Addressable Memory

Definition:

In word-addressable memory, each address refers to a word, not a byte. A word is a group of bytes (typically 2, 4, or 8 bytes depending on the system).

Example:

If the word size = 4 bytes, and the address 1000 refers to a full 4-byte word:

You cannot directly access individual bytes.

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4. Key Differences

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5. Why It Matters in OS:

• Affects how instructions access memory.

• Influences instruction set architecture (ISA).

• Impacts alignment, pointers, and data structures.

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Example for GATE / Exams:

Q: A system uses 32-bit word-addressable memory and each word has 4 bytes. What is the size of the memory if it has 2^20 addresses?

A:
Memory size = 2²⁰ * 4 bytes = 4 MB

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Summary:

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A visual diagram for this?
Practice questions or memory layout problems?

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Part 01- Operating Systems – Memory representation Techniques Byte Addressable and Word Addressable

Computer Organization and Architecture Tutorial Session

COMPUTER ORGANIZATION AND ARCHITECTURE

UNIT III Memory Organization

UNIT-III THE MEMORY SYSTEM

computer organization and architecture