Understanding Memory Hierarchy By: Tabish Saleem Date:13112024 What is Memory Hierarchy? Memory Hierarchy refers to the structure of different types of memory in a computer system arranged in levels based on Speed ,Cost and Size. Common
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What is Memory Hierarchy? Memory Hierarchy refers to the structure of different types of memory in a computer system arranged in levels based on Speed ,Cost and Size.
Common levels: Registers, Cache, Main memory(RAM) and Secondary Storage(Hard disk, SSD).<br>
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Levels of Memory Hierarchy Registers:
Fastest and Smallest form of Memory.
Located inside the CPU.
Stores temporarily Data, Variables and
results of calculation.
Cache Memory:
Cache memory is used to store frequently accessed data to reduce the time the CPU takes to fetch data from the slower RAM.<br>
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Levels of Memory Hierarchy Main memory(RAM):
Larger than Cache memory.
Volatile: Data is lost when the system is powered off.
Temporarily stores Data and Programmes that are currently in use.
Secondary storage:
Non-volatile storage(Data is retained even when the computer is turned off).
Examples: HDD, SSD.
Slower compared to primary memory, but much larger in capacity.
Tertiary and offline storage:
Optical media (CDs, DVDs), magnetic types, or cloud storage.
Used for backup.
Slowest, with much larger capacities.<br>
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Characteristics of memory levels<br>
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Why is Memory Hierarchy important? Speed: Slower memory (like registers and cache)is closer to the processor, reducing the time it takes to fetch data.
Cost –Effectiveness: Larger, Slower memory is cheaper and used for bulk storage .
Efficiency: Memory Hierarchy ensures that frequently accessed data is readily available.<br>
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Cache Memory –Levels explained L1 Cache: Smallest and fastest located within CPU Core. Stores data and instructions.
L2 Cache: Larger than L1. Stores data that is less frequently used than L1
L3 Cache: Plays an important role in data sharing and inter-core communication. Slower than L1 and L2 but still much faster than RAM.<br>
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Performance impact of Memory Hierarchy Access time: As you move from Registers to Secondary storage ,access time increases.
Cost per Bit: The Cost of Memory decreases as you move downwards in the hierarchy (Registers>Cache>RAM>Secondary storage)
Capacity: Larger storage devices( like SSD’S and HDD’s) are slower but provides much higher capacity compared to faster memories like Cache or RAM.<br>
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Types of Memory Hierarchy Volatile Memory:
Requires power to maintain data.
Examples:Registers, Cache ,RAM.
Non-Volatile Memory:
Retains data even when system is powered off.
Examples:HDD,SSD,ROM.<br>
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Data Access Flow CPU requests data.
Check in Registers: If available, access the data immediately.
Check Cache: If not in Registers, check the Cache for faster retrieval.
Check Main Memory(RAM):If not in Cache access the slower main memory<br>
