Monday 9 November 2020

OS Segmentation with Paging

 

Segmentation with Paging:

 

Both paging and segmentation have their advantages and disadvantages. It is better possible to combine these two schemes to improve on each. The combined scheme was ‘Page the segments’. Each segment in this scheme is divided into pages and each segment maintains a page table. So, the logical address is divided into 3 parts <S, P, D>.One is the segment number (S), second is the page number (P) and another is a displacement or offset (D). Consider the following fig:

Paged Segmentation

Fig: Paged Segmentation


The logical address space is divided into three segments number from 0 to 2. Each segment maintains a page table. The mapping between page and frame is done by page table. For ex: the frame number 8 shows the address (1, 3); where 1 stands for segment and 3 stands for page number. The main advantage of this scheme is to avoid fragmentation. It supports user view of memory. The hardware support of this combined scheme is shown in the following figure.


Paged segmentation memory management scheme

Fig: Paged segmentation memory management scheme



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