CSC 342 Computer Operating Systems: Main Memory Study Notes

What must be done for a program to run in memory?

The program must be brought from disk into memory and placed within a process.

What are the only storage types that the CPU can access directly?

Main memory and registers are the only storage types that the CPU can access directly.

What is the purpose of the base and limit registers?

A pair of base and limit registers define the logical address space. The CPU checks memory access to ensure it is within the limits for that user.

What are logical and physical addresses?

A logical address is generated by the CPU (also called a virtual address), while a physical address is the actual address seen by the memory unit.

What is the function of the Memory-Management Unit (MMU)?

The MMU maps virtual addresses to physical addresses at runtime.

What is dynamic relocation?

Dynamic relocation uses a relocation register to map logical addresses to physical addresses, allowing routines to not be loaded until called.

What is context switch time?

Context switch time includes the time to swap out a process and swap in the target process, which can be very high, especially for large processes.

What is contiguous allocation in memory management?

Contiguous allocation is an early method of memory management that allocates memory in contiguous sections for OS and user processes.

What is fragmentation in memory allocation?

Fragmentation occurs when processes cannot be assigned to memory blocks due to their small size; it can be internal or external.

What is the difference between internal and external fragmentation?

Internal fragmentation occurs when allocated memory is slightly larger than requested, while external fragmentation happens when total memory exists to fulfill a request, but it is non-contiguous.

What is a segment in segmentation?

A segment is a logical unit of a program that can include main programs, procedures, functions, and more.

How does paging avoid problems of fragmentation?

Paging divides physical memory into fixed-sized blocks called frames, thus avoiding external fragmentation and the need for compaction.

What is a page table?

A page table is a data structure used in paging that maps logical addresses to physical addresses.

What is the purpose of the translation look-aside buffer (TLB)?

The TLB is a special fast-lookup hardware cache that helps solve the two memory access problem in a paging environment.