Segment Table

Definition

A segment table is a data structure used in segmentation memory management to keep track of the various segments of a process. Each entry in the segment table contains information about a segment, such as its base address in physical memory and its length, allowing for efficient memory access and protection. By using a segment table, the operating system can enable logical segmentation of processes, facilitating easier management of memory and support for user-defined data structures.

5 Must Know Facts For Your Next Test

1. The segment table allows for dynamic sizing of segments, which can vary in length according to the needs of the program, as opposed to fixed-size pages.
2. Each process has its own segment table, enabling isolation and protection of segments belonging to different processes.
3. When accessing a segment, the operating system checks the segment table to validate addresses, ensuring they are within the defined limits for that segment.
4. The use of a segment table simplifies sharing and protection of code and data between processes by controlling access permissions at the segment level.
5. Segment tables may also include additional information like access permissions (read, write, execute) for each segment to enforce security.

Review Questions

• How does the segment table enhance memory management compared to traditional fixed-size paging?
  • The segment table enhances memory management by allowing for variable-sized segments that can more closely match the logical structure of a program. This means that instead of breaking programs into fixed-size pages, which may lead to wasted space, segmentation allows segments to be created according to specific needs like functions or arrays. This flexibility improves efficiency and can reduce fragmentation compared to traditional paging methods.
• Discuss how a segment table contributes to process isolation and security in a multitasking environment.
  • In a multitasking environment, each process has its own segment table that keeps track of its specific segments, providing clear boundaries between processes. This means that one process cannot access another process's segments without permission, thereby ensuring isolation. The segment table also includes access permissions for each segment, which enhances security by preventing unauthorized access to sensitive data or code within different processes.
• Evaluate the role of segment tables in supporting user-defined data structures and how this impacts programming practices.
  • Segment tables play a critical role in supporting user-defined data structures by allowing programmers to define segments based on logical needs rather than rigid memory constraints. This impacts programming practices by promoting better organization of code and data, as programmers can create segments that reflect their design intentions. As a result, it leads to improved maintainability and modularity in software development since changes can be made within segments without affecting others.

Related terms

Segmentation: A memory management technique that divides a program into different segments based on the logical structure, such as functions or data types, rather than fixed-size blocks.

Page Table: A data structure used in paging memory management that maps virtual addresses to physical addresses, maintaining information about which pages are stored in memory.

Base and Limit Registers: Registers used in segmented memory systems to define the boundaries of segments, where the base register holds the starting address and the limit register holds the length of the segment.