Process Control Blocks
a. In the context of Windows or UNIX Operating Systems, List and explain the essential attributes of a process control block (PCB).
Many simple and complex operations are being performed when the operating system (OS) creates processes. Information such as registers, quantum, priorities, and others are being stored in a Process Control Block. Logically all the process control blocks for each of the processes in the system are stored in the process control table defined as an array. A process control block has similar attributes, which are equally crucial for both Operating systems, Windows, and UNIX.
- Pointer – To maintain position of the process, this stack pointer is stored in the event where the state of the process is being switched to another state.
- Process State – This state stores the state of the processes such as waiting, new, running, etc.
- Process Counter – Process number is also known as the process ID. PID is assigned to every process to distinguish between processes
- Program Counter – Program counters execute instructions as it counts and contains the upcoming instruction’s address.
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- Register – GPR (General Purpose Registers), registers, base and accumulators are the registers used as CPU registers in PCB.
- Memory Limits – Memory Limits deals with data regarding the management of memory in the system. Segment tables and page tables are some of the examples which are included in it.
- Open files list – The list contains the information regarding open files.
b. Explain the changes in the description of the state and resource allocation, which when a print job process has been interrupted before finishing for another print job process to start.
When a print job process is interrupted, the program counter already has the next instruction for the next print job. As the operations are being scheduled by the process scheduler; therefore, the second print job instruction does not execute until the first one is not completed. All resources are in halt state until parallelism is introduced.
Q2. Processes and Threads
a. Explain the difference between virtual memory and physical memory and describe the conditions that require the use of virtual memory.
- Physical memory:
Memory stored in a physical state such as hard drives is a type of storage device and chips which represents memory such as RAM; these are referred to be as physical memory. A process is loaded into a physical memory such as RAM in order to be executed.
- Virtual memory:
A process of interchanging data between RAM memory and hard drive or physical memory storage is known as virtual memory.
Virtual memory is practical to use as it enables us to work with extensive programs and expect an efficient performance. It comes handy when the computer needs to work with larger blocks of data or more comprehensive programs to execute.
b. Describe how disk swapping is used to implement virtual memory.
One of the other reasons to use virtual memory is disk swapping; due to this, it is implied that the computer contains a larger memory, which enables the programs to perform efficiently as the transfer of big blocks of data becomes easier.