PCB & Context Switching

PCB (Process Control Block)

• The Process Control Block (PCB) is a data structure used by the operating system to store *metadata about a process.
• It is created by the OS when a process is generated.
• The PCB contains all the essential information needed to manage and control the process.
• Since it holds critical information, it is protected and maintained at the front of the kernel stack, inaccessible to regular users.

When a program is executed, a process is created and memory (stack, heap, etc.) is allocated based on the process's memory structure.

At the same time, the OS stores the process's metadata in its PCB.

 

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What is *Metadata?

• Metadata is structured data that describes other data.
• It allows users or systems to efficiently locate and utilize specific information from a large dataset by providing standardized information about the content.

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Context Switching

• Context switching is the process of saving the current process’s PCB and loading another process’s PCB.
• It occurs when:
  • The allocated CPU time for a process expires.
  • An interrupt happens (e.g., I/O or higher-priority task).

Even though it seems like the computer runs many processes simultaneously,

only one process is actually executed at a time on a single CPU.

It appears concurrent because context switching happens so quickly between processes.