The VAX$/$VMS operating system makes use of four processor access modes to facilitate theprotection and sharing of system resources among processes. The access mode determines:Instruction execution privileges: What instructions the processor may executeMemory access privileges: Which locations in virtual memory the current instruction may accessThe four modes are as follows:Kernel: Executes the kernel of the VMS operating system, which includes memory management,interrupt handling, and I$/$O operations.Executive: Executes many of the OS service calls, including file and record $($disk and tape$)$management routines.Supervisor: Executes other OS services, such as responses to user commands.User: Executes user programs, plus utilities such as compilers, editors, linkers, and debuggers.A process executing in a less$-$privileged mode often needs to call a procedure that executes in amore$-$privileged mode; for example, a user program requires an operating system service. Thiscall is achieved by using a change$-$mode $($CHM$)$ instruction, which causes an interrupt thattransfers control to a routine at the new access mode. A return is made by executing the REI$($return from exception or interrupt$)$ instruction.a$.$ A number of operating systems have two modes: kernel and user. What are the advantages anddisadvantages of providing four modes instead of two?b$.$ Can you make a case for even more than four modes?