Part 01- Operating Systems – Memory representation Techniques Byte Addressable and Word Addressable
Part 01- Operating Systems – Memory representation Techniques Byte Addressable and Word Addressable
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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
1000stores 1 byte of data. - Address
1001stores 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
1000refers to a whole word (4 bytes). - Address
1001does 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?