Memory Management Flashcards
What is the primary function of memory management in Layer 3?
It ensures that processes and data are in primary memory (PM) for operation, manages competition for finite memory resources, and protects co-resident processes from one another
Define Virtual Address
A virtual address is relative to the start of a process’s address space and not the actual physical memory location
What is the difference between compile-time, load-time, and execution-time binding?
- Compile-time, memory addresses are fixed at compile time
- Load-time, addresses are determined when the program loads into memory
- Execution-time, addresses can change dynamically during execution
What are the three main goals when multiple programs share memory?
Transparency, safety, and efficiency
What is the difference between static and dynamic relocation?
- Static Relocation, memory mapping is done before or during process loading and cannot be moved afterward
- Dynamic Relocation, memory mapping is done at runtime, allowing processes to move freely in memory
What is external fragmentation?
It occurs when total memory is sufficient to satisfy a request, but it’s not contiguous
What are the advantages of paging?
- Simplifies memory allocation
- Eliminates external fragmentation
- Allows processes to use memory efficiently through logical segmentation
How does segmentation differ from paging?
- Segmentation divides memory into variable-sized logical segments
- Paging divides memory into fixed-sized blocks and removes the need for contiguous memory allocation
Memory allocation policies first fit?
Allocate the first hole that is big enough
- First fit and best fit usually yield better storage utilisation
- First fit is generally faster than best fit
Memory allocation policies best fit?
Allocate the smallest hole that is big enough
- Must search entire list, unless ordered by size
- Produces the smallest leftover hole
Memory allocation policies worst fit?
Allocate the largest hole
- Must also search entire list
- Produces the largest leftover hole
Memory allocation policies next fit?
Spread the allocations out more evenly across the memory space
Difference between a physical address and a virtual address?
- Physical address, is the actual location int eh computer’s memory hardware (RAM) where data or instructions are stored
- Virtual address, is an address used by a program or process to reference memory (abstraction)
Hardware support needed for a paged virtual memory
- Memory Management Unit (MMU)
- Translation Lookaside Buffer (TLB)
- Page table
- Support for paging, fixed size pages (frames)
Difference between internal fragmentation and external fragmentation
- Internal fragmentation, wasted memory that occurs inside allocated memory blocks because the allocated memory is slightly larger than the requested memory
- External fragmentation, wasted memory that occurs outside allocated memory blocks because free memory is divided into small, non-contiguous chunks, making it difficult to allocate to processes even if the total free memory is sufficient
Advantages of virtual memory
- Efficient use of physical memory, dynamic allocation and optimal utilisation
- Memory isolation and protection
- Support for multitasking, concurrency and efficient context switching
Disadvantages of virtual memory
- Performance overload, slower access and page faults
- Increased complexity
- Resource usage
- Thrashing (system runs out of physical memory and has to swap pages excessively between RAM and disk
What is relocation?
The ability to move process around in memory without it affecting its execution
What is paging?
- Divides and assigns processes to fixed sized pages
- Selectively allocate pages to frames in memory
- Manages pages in memory
What is segmentation?
Partition an address space into logical units with a segment number (mapped to a segment base address), and an offset from the beginning of that segment
