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    Memory Hierarchy Reference

    CPU cache levels, RAM types, and storage access times

    Memory Hierarchy Levels

    From fastest CPU registers to persistent storage

    CPU Registers

    Register

    Size

    < 1 KB

    Latency

    ~1 cycle

    Bandwidth

    > 1 TB/s

    Technology

    SRAM cells

    Relative Latency (log scale)
    Inside CPU core

    L1 Cache

    Cache

    Size

    32-64 KB

    Latency

    ~4 cycles

    Bandwidth

    > 500 GB/s

    Technology

    SRAM

    Relative Latency (log scale)
    Per CPU core

    L2 Cache

    Cache

    Size

    256-512 KB

    Latency

    ~14 cycles

    Bandwidth

    > 200 GB/s

    Technology

    SRAM

    Relative Latency (log scale)
    Per CPU core

    L3 Cache

    Cache

    Size

    8-32 MB

    Latency

    ~42 cycles

    Bandwidth

    > 100 GB/s

    Technology

    SRAM

    Relative Latency (log scale)
    Shared between cores

    Main Memory (RAM)

    DRAM

    Size

    8-64 GB

    Latency

    ~100 ns

    Bandwidth

    25-100 GB/s

    Technology

    DDR4/DDR5

    Relative Latency (log scale)
    DIMM slots
    5/GB

    NVMe SSD

    Storage

    Size

    256 GB - 8 TB

    Latency

    ~20 μs

    Bandwidth

    3-7 GB/s

    Technology

    NAND Flash

    Relative Latency (log scale)
    PCIe slot
    0.1/GB

    SATA SSD

    Storage

    Size

    128 GB - 4 TB

    Latency

    ~100 μs

    Bandwidth

    550 MB/s

    Technology

    NAND Flash

    Relative Latency (log scale)
    SATA port
    0.08/GB

    HDD

    Storage

    Size

    1-20 TB

    Latency

    ~10 ms

    Bandwidth

    150 MB/s

    Technology

    Magnetic

    Relative Latency (log scale)
    SATA port
    0.02/GB

    Key Insights