Memory System

18CS34 | COMPUTER ORGANIZATION | Module-3 VTU Notes

VTU | 18CS34 | Module - 3

Memory System, Cache Memories, and Performance Considerations

The memory system is a critical component of computer architecture, affecting speed, efficiency, and cost. This summary covers fundamental memory concepts, semiconductor RAM and ROM memories, as well as cache memories, including mapping, replacement algorithms, and performance considerations.

Basic Concepts:

Memory is a core component of a computer system, responsible for storing data and instructions. Memory hierarchy includes different levels of memory, each with varying access speeds, sizes, and costs. The trade-off between these factors is crucial for system performance.

Semiconductor RAM Memories:

Random Access Memory (RAM) is volatile memory that provides fast read and write access. Dynamic RAM (DRAM) and Static RAM (SRAM) are common semiconductor RAM types. DRAM is cost-effective but requires periodic refreshing, while SRAM is faster and more stable but more expensive.

Read-Only Memories (ROM):

Read-Only Memories are non-volatile memories that store data that remains even when power is lost. Programmable ROM (PROM), Erasable PROM (EPROM), and Electrically Erasable PROM (EEPROM) are variants with different levels of reprogrammability.

Speed, Size, and Cost:

Memory characteristics, including speed, size, and cost, influence system performance. Faster memories are more expensive and smaller, while slower memories offer larger capacities at a lower cost.

Cache Memories:

Cache memory is a high-speed, small-capacity memory that stores frequently used data to reduce the time taken to access main memory. It mitigates the memory speed gap between the CPU and main memory.

- Mapping Functions: Cache mapping determines how data is placed in the cache. Common techniques include direct mapping, set-associative mapping, and fully associative mapping.

- Replacement Algorithms: When a cache is full, a replacement algorithm determines which data to evict to make space for new data. Algorithms like Least Recently Used (LRU), First-In-First-Out (FIFO), and Random are used.

- Performance Considerations: Cache performance relies on hit rate (how often requested data is found in the cache) and miss rate (how often requested data is not found). Cache size, associativity, and replacement policies affect cache performance.

Understanding memory systems, cache principles, and their associated performance considerations is pivotal for optimizing computer system design. An effective memory hierarchy enhances system responsiveness and efficiency, facilitating the seamless execution of various tasks. The trade-offs between memory speed, size, and cost, along with cache optimization, ensure that the memory system meets the demands of modern computing workloads.