43、The kerel has full access to the system＇ s memory and must allow processes to access safely this memory as they require it.Often the first step in doing this is Virtual addressing, usually achieved by paging and/or segmentation.Virtual addressing allows the kerel to make a given physical address appear to be another address, the virtual address.Virtual address spaces may be different for different processes; the memory that one process accesses at a particular ( ) address may be different memory from what another process accesses at the same address.This allows every program to behave as fit is the only one ( ) running and thus prevents applications from crashing each other.On many systems, a program＇s virtual address may refer to data which is not currently in memory.The layer.of indirection provided by virtual addressing allows the operating system to use other data stores, like a hard drive, to store what would otherwise have to remain in main memory ( ).As a result, operating systems can allow programs to use more memory than the system has physically available.When a program needs data which is not currently in RAM, the CPU signals to the kernel that this has happened, and the kernel responds by writing the contents of an inactive memory block to disk ( ) and replacing it with the data requested by the program.The program can then be resumed from the point where it was stopped.This scheme is generally known as demand paging.
Virtual addressing also allows creation of virtual partitions of memory in two disjointed areas, one being reserved for the kernel ( ) and the other for the applications ( ).The applications are not permitted by the processor to address kerel memory, thus preventing an application from damaging the running kerel.This fundamental partition of memory space has contributed much too current designs of actual general-purpose kerels and is almost universal in such systems, although some research kernels take other approaches.(1)、 Which of the following statements about virtual addressing is wrong?