unit4

Unit IV: Memory Organization

Memory Hierarchy

• The goal of memory hierarchy is to achieve the highest possible access speed while minimizing the cost of the entire memory system.

• Components of memory hierarchy include:

  • Main Magnetic Memory: Magnetic memory tapes used for data.

  • I/O Processors: Manage input/output operations for the CPU.

  • Cache Memory: Fast storage.

  • Magnetic CPU Disk Storage: Commonly used storage types with varying capacities (e.g., 1KB, 1GB).

• Access speed is essential for performance.

Main Memory Components

• Main Memory includes:

  • RAM (Random Access Memory) and ROM (Read-Only Memory) chips.

  • A typical setup may include chipselect (CSI ESI) which addresses data bits.

• RAM configurations use various chips:

  • Dynamic RAM (DRAM) and Static RAM (SRAM)

  • PROM (Programmable ROM), EPROM (Erasable Programmable ROM), and EEPROM (Electronically Erasable Programmable ROM).

• The connection to the CPU is crucial for the performance of the programs running on it.

Auxiliary Memory

• Also known as backup storage, consists of devices like:

  • DVD, CD, floppy disks, and pendrives.

• Features the use of tracks and read/write heads for magnetic disks.

Associative Memory

• Content Addressable Memory (CAM) allows for:

  • Fast data retrieval by specifying content rather than the address.

• Key Registers such as Augment Register (A), Key Register (k), and Match Register (M) manage data matching during retrieval.

• Block Diagram illustrates the structure of associative memory.

Cache Memory

• Designed for speed, typically with 32K x 12 data bits.

• Cache memory improves access time by serving frequently used data from a faster, smaller retail memory.

• Hit Ratio calculation: No. of hits / (No. of hits + No. of misses).

• Miss: When requested data is not found in cache;

• Hit: When the requested data is found in cache.

Types of Mapping Techniques in Cache Memory

• Associative Mapping:

  • Utilizes the address in the argument register (A).

  • Example: 15 bits for CPU address, transforming data into cache memory for quicker retrieval.

• Direct Mapping:

  • Maps each block of main memory to a specific block of the cache.

  • Involves tag and index for efficient data fetching.

• Set Associative Mapping:

  • Combines features of both associative and direct mapping to improve cache hits.

Virtual Memory

• Virtual memory allows programs to act as if they have access to a large memory space despite actual physical constraints.

• It enables the user to work with larger datasets by managing data between auxiliary and main memory.

  • Auxiliary Memory: Long-term storage where programs/data initially reside.

  • Physical Address & Virtual Address: Managing memory mapping to enhance performance.

• Address space is determined based on the overall memory architecture (e.g., 32K, 1024K).

Virtual Address Mapping

• Structured with main registers and memory tables.

• The virtual memory address mapping connects virtual addresses to physical memory locations through a table that includes lines for blocks of memory.

• Each block in the virtual and physical addresses is correlated, providing efficient retrieval and use of memory resources.