In-Depth Notes on Memory Management and Process State Management

Memory management involves efficiently allocating and deallocating memory within the operating system (OS).

OS oversees the life-cycle of all processes in memory, managing their states like running, ready, and blocked.

Base Register: Physical address pointing to where the process is loaded in memory.
Limit Register: Specifies the allowed range of addresses for that process, allowing access via offsets from the base address.
Both registers are crucial for memory separation and management, especially in contiguous memory allocation.

Traditionally, processes needed contiguous blocks of memory, making allocation straightforward but prone to fragmentation.
Overview of processes in memory:
- Each process is represented by its data, program code, and registers.

Degree of Multiprogramming: Number of processes that can execute simultaneously.
Achieved primarily by increasing main memory size or adopting virtual memory systems.
Virtual Memory: Allows processes to use a larger address space than the physical memory, utilizing secondary storage when necessary.

Memory Allocation: Assigning memory to processes as needed.
Deallocation: Freeing up memory when processes terminate or are swapped out.
Address Space Isolation: Protecting each process's address space from interference by others.
Virtual Memory Management: Facilitating switching processes in and out of main memory based on current usage.
Address Translation: Converting logical addresses generated by processes to physical addresses in RAM.

Relocation: Processes may not occupy the same memory location upon reallocation. The OS needs to manage this seamlessly.
Protection: Preventing one process from accessing memory allocated to another, achieved through logical address spaces.

Involves translating logical addresses (used by the process) to physical addresses (actual memory locations).
Utilizes Base and Limit Registers:
- Base register: Defines where the process starts.
- Limit register: Defines the size of the addressable space for the process.
The Memory Management Unit (MMU) handles address translation by adding the base register value to the logical address and checking against the limit register.

Allows for the changing of physical location without modifying the process itself. The base register is updated upon recollecting the process.

Variable-sized Partitioning: Memory is dynamically partitioned into sizes based on process requirements.
Fragmentation: Smaller holes may arise, complicating new allocations.
Compaction: Periodic shifting of processes facilitates reduction of fragmentation by merging free spaces.

Modern OS typically uses paging instead of contiguous allocation, dividing memory into fixed-sized pages, thus removing fragmentation challenges.
Each process's address space consists of multiple non-continuous pages, with multiple pages per process potentially resident in non-continuous frames of physical memory.

Virtual and physical memory is divided into pages, and the mapping of these via a page table helps in management.
Each address comprises:
- Page number: Index to the page table.
- Offset: Location within the page.
The MMU translates logical addresses into physical addresses, enhancing efficiency and performance without the need for contiguity.

TLB (Translation Lookaside Buffer): Cache for quick access to page table entries, reducing translation time and improving system performance.
TLB size generally varies from 32 to 1024 entries, with a hit leading to faster address resolution compared to a miss, which may require a page table lookup.