Virtual Address Space in Operating System

In operating systems, Virtual memory plays a very vital role, in managing the memory allotted to different processes and efficiently isolating the different memory addresses. The role of the virtual address is to assign a space to the ledger of all the virtual memory areas that are provided to different processes. This process enables the process to view the respective memory independently and be more flexible and maintainable.

What is Virtual Address Space in an Operating System?

Virtual address space refers to the room of addresses which usually refers to the reference to the different slots of virtual memory allotted to different processes. Operating systems allocate this set of addresses for the processes to use in order to access their designated virtual memory. The address space is divided into many regions, each of which serves a specific function. An operating system’s processes each have their own distinct virtual memory space, where all of their addresses are kept. Every process, therefore, creates the illusion that they have dedicated physical memory as a result of this characteristic.

Key Terminologies of Virtual Address Space in Operating System

• Page: A page is a fixed-size memory block that is used to manage virtual memory.
• Code segment: A part of a virtual address that contains the executable instructions of the process.
• Data Segment: The part of a virtual address that contains the allocated memory and process variables.
• Page Table: It is a data structure that the operating system manages to keep track of the relationship between virtual pages and actual memory frames.
• Page Fault: This is a case scenario where the page which is requested is not present in the physical memory.

Characteristics of Virtual Address Space

• Virtual address space enables dynamic memory allocation as it is mainly needed to carry out the task of assigning memory blocks to the processes when they request dynamically.
• A page table is used to maintain the mapping of the Virtual address to the corresponding Physical address which can be referred to as address translation which is used by the Virtual address space to maintain the mapping.
• The Virtual address space also contains the different access specifiers for specific virtual memory blocks that specify whether a space will be read-only, read-write access, or no access. This ensures that the memory or data is safe from any misdoings.
• Using Virtual Address Space to give the processes are independent of any running process, as they have noninterfering virtual address space.
• This technique when used to enable memory sharing as helps to map the specific virtual memory addresses to the same physical memory so that two/more processes can use the same memory space to make more efficient use of it.

Virtual Address Space

How Does Virtual Address Space Works in Operating System?

• The Virtual Address Space’s working starts with the allocation of the virtual address space’s single page to the individual process as soon as a process is created.
• The Virtual Address Space has two spaces and their individual jobs:
  • The instruction statements which are attached to the process are stored in the code segment of the address space to execute them when needed.
  • All the process variables and data of the process are stored in the Data segment of the address space to make them more accessible.
• The operating system uses the Page Table to get the virtual address to access the virtual page frame which is linked to the Physical address in the Physical memory using the Page table.
• The Virtual Addresses have both the virtual page number of the individual pages and the page offset which is used to combine with the physical page number from the page table to get the actual physical address.
• When the required page is not present in the Physical memory the OS fetched it from the secondary memory which is the hard disk and swapped it to any available page frame in the memory. This function is executed using the Page Replacement Algorithms in Operating Systems.

Advantages of Using Virtual Address Space in Operating System

• Allows efficient memory management and helps to avoid fragmentation issues
• Using this technique gives memory protection as it helps to prevent the virtual memory frames from getting accessed anonymously.
• Avoids interference between processes’ memory spaces which helps to increase the stability of the system.
• It helps to make efficient usage of the memory as it helps to share the same memory space for two/more processes.

Disadvantages of Using Virtual Address Space in Operating System

• Using the Virtual Adress Space process adds more complexity to the memory management system as there are several steps that are carried on to make it work.
• Managing the Page table is more work and it also adds to the increase in complexity of the process.
• Additional space is used to include the Page Table which maintains the mapping between the virtual and physical memory.

Conclusion

In general, virtual address space is essential for an operating system’s effective and safe memory management. It gives processes access to an isolated and expanded memory environment that allows them to run effectively while maintaining the security and stability of the system.

FAQs on Virtual Address Space

1. How is an operating system’s virtual address space divided?

Pages are the standard fixed-size units used to split virtual address space. Each page corresponds to a block of memory, and the operating system manages the mapping between virtual pages and physical memory using a page table.

2. Can a virtual address be shared by numerous processes?

Several processes can share a single virtual address, yes. Since each process has a distinct virtual address space, various physical memory locations are referenced by the same virtual address in different processes.

3. What occurs when a process accesses a virtual address that isn’t associated with any physical memory?

A page fault occurs when a process accesses a virtual address that is not currently mapped to physical memory. Before enabling the operation to continue, the operating system first establishes the mapping by retrieving the matching page from secondary storage (such as a hard disc) and updating the page table.