A page frame, a fixed-size block of physical memory, typically has a standard size, but can also exist in larger sizes depending on the system architecture and configuration.
While a common default size for a page frame is 4 KB (kilobytes), page frames can also be significantly larger, such as 1 MB (megabyte) or even larger on some systems.
The choice of page frame size can impact system performance, but the use of larger sizes may come with certain constraints, especially in specific memory areas.
Common Page Frame Sizes
Different systems and configurations support various page frame sizes. The most frequently encountered size is relatively small, designed for efficient memory utilization.
- Default/Standard Size: Often 4 KB. This size is widely supported and acts as a fallback when larger sizes are not permitted.
- Larger Sizes: Systems can support larger page frames like 1 MB or even 2 MB, 4 MB, or 1 GB. These larger sizes, sometimes called "large pages" or "huge pages," can improve performance for applications that use large amounts of contiguous memory by reducing the overhead associated with managing smaller pages.
Memory Allocation Constraints
Using larger page frame sizes is often subject to rules based on where the memory is located. According to the provided reference:
- Below the 16-MB Line: Page frame sizes larger than 4 KB are generally not allowed below this specific memory address boundary.
- Example: If a configuration specifies using 1 MB page frames, but the storage is allocated in the memory area below the 16-MB line, the system will default back to using 4 KB page frames instead for that specific allocation.
This constraint ensures compatibility or addresses specific hardware limitations associated with older memory addressing schemes or device access within lower memory regions.
Why Different Sizes?
Different page frame sizes are used for various reasons:
- Efficiency: Smaller pages (like 4 KB) help minimize internal fragmentation (wasted space within the last page of a process's memory).
- Performance: Larger pages (like 1 MB or more) can improve performance by:
- Reducing the number of entries needed in the Translation Lookaside Buffer (TLB), a cache that speeds up virtual-to-physical address translation.
- Decreasing the overhead of managing page tables for processes that require large contiguous blocks of memory.
In summary, while 4 KB is a very common page frame size and often the default or required size in certain memory regions (like below the 16-MB line), larger sizes like 1 MB are also used to enhance system performance for suitable workloads.
