37 What is the difference between logical and physical address space
8.1.3 Logical Versus Physical Address Space
Logical addressAn address generated by the CPU.Physical addressAn address seen by the memory unit and loaded into the memory-addressregister.Logical address spaceThe set of all logical addresses generated by a program.Physical address spaceThe set of all physical addresses corresponding to these logical addresses.Memory-management unit (MMU)Run-time map from virtual to physical addresses.The user program never sees the real physical addresses and deals with logicaladdresses.The memory-mapping hardware converts logical addresses into physical addresses
8.3 Contiguous Memory Allocation
The memory is usually divided into two partitions: * one for the resident operating system and * one for the user processes.Contiguous memory allocationEach process is contained in a single section of memory that is contiguous tothe section containing the next process.
8.3.1 Memory Protection
* The relocation register contains the value of the smallest physical address. * The limit register contains the range of logical addresses.
8.3.2 Memory Allocation
One of the simplest methods for allocating memory is to divide memory intoseveral fixed-sized partitions.Thus, the degree of multiprogramming is bound by the number of partitions. * In this multiple-partition method, when a partition is free, a process is selected from the input queue and is loaded into the free partition. * In the variable-partition scheme, the operating system keeps a table indicating which parts of memory are available and which are occupied.Dynamic storage-allocation problem concerns how to satisfy a request of size$n$ from a list of free holes. There are many solutions to this problem: * First fit * Best fit * Worst fitSimulations have shown that both first fit and best fit are better than worstfit in terms of decreasing time and storage utilization. Neither first fit norbest fit is clearly better than the other in terms of storage utilization, butfirst fit is generally faster.
8.4.2 Segmentation Hardware
A logical address consists of two parts: * a segment number: $s$ * an offset into that segment: $d$Segment table consists of * a segment base: contains the starting physical address where the segment resides in memory. * a segment limit: specifies the length of the segment.
Operating System Interview Question
A list of top frequently asked Operating System interview questions andanswers are given below.
16) What is virtual memory?
Virtual memory is a very useful memory management technique which enablesprocesses to execute outside of memory. This technique is especially used whenan executing program cannot fit in the physical memory.* * *
26) What is the difference between logical address space and physical
address space?Logical address space specifies the address that is generated by CPU. On theother hand physical address space specifies the address that is seen by thememory unit.* * *
37) What is the difference between logical and physical address space?
Logical address specifies the address which is generated by the CPU whereasphysical address specifies to the address which is seen by the memory unit.After fragmentation* * *
What is Process Address Space?
Address space is a space in computer memory. And process Address Space means aspace that is allocated in memory for a process. Every process has an addressspaceAddress Space can be of two types 1. Physical Address Space 2. Virtual Address Space
Physical address space
he physical address is the actual location in the memory that existphysically. System access the data in the main memory, with the help ofphysical address. Every thing in the computer has a unique physical address.We needs to mapped it to make the address accessible. MMU is responsible formapping.
Virtual Address Space
Virtual Address Space is an address space that is created outside the mainmemory inside the virtual memory, and it is created in the hard disk.When our main memory is less and we want to get more benefit from this lessmemory, then we create virtual memory.Logical Address is the address is always generated by CPU while running aprogram. The logical address is also called virtual address. Virtual addressdoes not exist physically, so we can say that physical address is the logicaladdress. How to access the physical memory location by CPU? Logical Address is used as a reference to access the physical memory locationby CPU. The Memory-Management Unit uses the address-binding methods formapping the logical address to its corresponding physical address.PARAMENTER | LOGICAL ADDRESS | PHYSICAL ADDRESS —|—|— Basic | ADDRESS generated by CPU is called LOGICAL ADDRESS. | PHYSICAL ADDRESSis the actual location in a memory unit. Generation | generated by the CPU | Computed by MMU Access | logical address can be used to access the physical address by theuser. | The user can’t directly access physical address but it is possibleindirectly. Visibility | logical address of a program is visible to the user. | physicaladdress of program is not visible to the user. Address Space | set of all logical addresses generated by CPU are calledlogical addresses. | Addresses mapped to the corresponding logical addresses.