Practice_Question_Os_physical Addressing
Duration: 2 min
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AI Summary
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The video presents a problem involving memory management in operating systems, specifically focusing on the use of relocation and limit registers to determine valid memory access. The instructor displays a table listing five processes (P0 to P4) with their corresponding Limit and Relocation register values. Below the table, a list of logical address requests from these processes is provided. The core task is to evaluate each request to determine if it is legal (within bounds) or illegal (out of bounds) and, if legal, to calculate the resulting physical address. The instructor systematically analyzes each process request, comparing the requested logical address against the process's limit register value. For valid requests, he demonstrates the calculation of the physical address by adding the logical address to the base address found in the relocation register.
Chapters
0:00 – 2:00 00:00-02:00
The instructor begins by analyzing the first request from process P0, which is 450. He checks the limit register for P0, which is 500. Since 450 is less than 500, he marks it as legal. He then calculates the physical address by adding the logical address (450) to the relocation register value (1200), resulting in 1650. Next, he moves to P1 with a request of 300. The limit register for P1 is 275. Since 300 is greater than 275, he marks this attempt as illegal. He proceeds to P2 with a request of 210. The limit is 212, so 210 is valid. He calculates the physical address as 880 + 210 = 1090. Then, for P3, the request is 450, but the limit is 420, making it illegal. Finally, he addresses P4 with a request of 80. The limit is 118, so it is legal, and the physical address is calculated as 200 + 80.
2:00 – 2:16 02:00-02:16
The instructor completes the calculation for process P4. He writes down the sum of the relocation register (200) and the logical address (80), resulting in a physical address of 280. He circles the final answer and briefly concludes the problem-solving session, having successfully identified the illegal attempts and calculated the physical addresses for the valid ones.
The lesson effectively demonstrates the mechanism of address binding and protection in memory management. By comparing logical addresses against limit registers, the system ensures processes do not access unauthorized memory regions. The addition of the relocation register value shifts the logical address space to the correct physical location, illustrating how dynamic relocation works in a multitasking environment.