Operating System Concepts: Memory Hierarchy

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Questions and Answers

What is the basic composition of memory?

A large array of words or bytes, each with its own address

What does the memory unit see when it receives requests?

A stream of memory addresses, read requests, or address + data and write requests

What is the purpose of cache in a computer system?

To sit between main memory and CPU registers

Why is protection of memory required in a computer system?

To ensure correct operation and prevent unauthorized access Signup and view all the answers

How long does it take to access a register?

One CPU clock (or less) Signup and view all the answers

What is the role of the program counter in the CPU?

It provides the memory address for the CPU to fetch instructions Signup and view all the answers

What is the main purpose of a page table in a computer system?

The main purpose of a page table is to provide the corresponding frame number (base address of the frame) where that page is stored in the main memory. Signup and view all the answers

What is the purpose of the page number in the address scheme mechanism?

The page number is used as an index into a page table which contains the base address of each page in physical memory. Signup and view all the answers

What is the function of the page offset in the address scheme mechanism?

The page offset is combined with the base address to define the physical memory address that is sent to the memory unit. Signup and view all the answers

What is the logical address 0 mapped to according to the given paging example?

Physical address 20. Signup and view all the answers

What is the page table in the context of operating systems?

The page table is a data structure used by the operating system to store the mapping between physical and logical addresses. Signup and view all the answers

How is the logical address 4 mapped to a physical address?

Page 1 is mapped to frame 6, and the offset is 0, so the physical address is 24 (= (6 x 4) + 0). Signup and view all the answers

What is the size of each page in the given paging example?

4 bytes. Signup and view all the answers

How is the logical address translated into a physical address?

The logical address is translated into a physical address with the help of the page table. Signup and view all the answers

What happens when a process is terminated and a new process is loaded from the ready queue into main memory?

The page table is updated to reflect the new process's page mapping. Signup and view all the answers

How many pages are there in the physical memory of 32 bytes?

8 pages. Signup and view all the answers

What is the relationship between the logical address space and the page size in a paging system?

The logical address space is 2m and the page size is 2n. Signup and view all the answers

What is the role of the page table in the paging model of logical and physical memory?

The page table provides the mapping between logical addresses and physical addresses. Signup and view all the answers

What is the primary function of relocation registers in contiguous allocation?

To protect user processes from each other and from changing operating-system code and data. Signup and view all the answers

How does the MMU map logical addresses in contiguous allocation?

Dynamically. Signup and view all the answers

What is the limitation of multiple-partition allocation in terms of multiprogramming?

The degree of multiprogramming is limited by the number of partitions. Signup and view all the answers

What happens to a process's allocated memory when it exits?

The partition is freed and adjacent free partitions are combined. Signup and view all the answers

What information does the operating system maintain about memory allocation?

Information about allocated partitions and free partitions (holes). Signup and view all the answers

What is the dynamic storage-allocation problem?

How to satisfy a request of size n from a list of free holes. Signup and view all the answers

What is the purpose of associating a protection bit with each frame in a paging system?

To indicate if read-only or read-write access is allowed. Signup and view all the answers

What is the significance of the 'valid' bit in a page table entry?

It indicates that the associated page is in the process' logical address space. Signup and view all the answers

What is the advantage of sharing read-only code among processes?

It allows multiple processes to share the same code, reducing memory usage. Signup and view all the answers

What is the difference between shared and private code and data?

Shared code and data are shared among processes, while private code and data are specific to each process. Signup and view all the answers

What happens when a process attempts to access a page that is marked as 'invalid'?

A trap to the kernel occurs. Signup and view all the answers

What is the purpose of adding additional bits to the protection bit in a paging system?

To indicate additional access privileges, such as page execute-only. Signup and view all the answers

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