Memory Hierarchy

Memory Hierarchy

An arrangement of storage types organized by speed, cost, size, and proximity to the CPU.

Volatility

Whether stored data is lost when power is removed.

Memory Density

The amount of data that can be stored per unit volume.

Access Speed

The time required to read or write data from a storage device.

Access Size

The minimum unit of data that can be read or written (e.g., byte, word, page)

CPU Overhead

The amount of processing effort required by the CPU to manage a memory device.

Registers

Very small, extremely fast storage locations inside the CPU used for temporary data and control information.

Register Cost

High cost per byte, which limits the no. of registers available.

Main RAM

Medium-speed, Volatile memory used to store active data, stack, and sometimes program code.

Nonvolatile Memory

Memory that retains data without power, such as flash, EPROM, or hard disks.

Booting

The process of loading program code from nonvolatile storage into RAM after power-up.

Memory Hierarchy Trade-Off

As memory capacity increases and cost per byte decreases, access speed decreases.

Embedded vs Desktop Memory Hierarchy

Embedded systems typically use fewer memory layers, while desktop systems use many layers including cache, MMU, and secondary stage.

Memory Management Unit (MMU)

Hardware that manages memory addressing and protection, commonly used in desktop/server systems.

Cache Memory

Small, fast memory that stores frequently accessed data to reduce average memory access time.