UGC NET JULY 2018 (Computer Science And Applications Paper-II) (Question 54-55)
(A) I/O protection is ensured by operating system routines.
(B) I/O protection is ensured by a hardware trap.
(C) I/O protection is ensured during system configuration.
(D) I/O protection is not possible.
Answer : (A) I/O protection is ensured by operating system routines.
Explanation: Memory mapped I/O means, accessing I/O via general memory access as opposed to specialized IO instructions.
The programmer can directly access any memory location directly. To prevent such an access, the OS (kernel) will divide the address space into kernel space and user space. An user application can easily access user application. To access kernel space, we need system calls (traps).
Q 55. Which UNIX/Linux command is used to make all files and sub-directories in the directory “progs” executable by all users ?
(A) chmod− R a+x progs
(B) chmod −R 222 progs
(C) chmod−X a+x progs
(D) chmod −X 222 progs
Answer : (A) chmod− R a+x progs
Solution : Option A will make all files and sub-directories in the directory (progs) executable by all users.
-R is for recurssive calls, so that sub-directories within the directories can be accessed.
a is for all users
+x is for making things executable
Q 54. Normally user programs are prevented from handling I/O directly by I/O
instructions in them. For CPU's having explicit I/O instructions, such
I/O protection is ensured by having the I/O instructions privileged. In a
CPU with memory mapped I/O, there is no explicit I/O instruction. Which
one of the following is true for a CPU with memory mapped I/O ?
(A) I/O protection is ensured by operating system routines.
(B) I/O protection is ensured by a hardware trap.
(C) I/O protection is ensured during system configuration.
(D) I/O protection is not possible.
Answer : (A) I/O protection is ensured by operating system routines.
Explanation: Memory mapped I/O means, accessing I/O via general memory access as opposed to specialized IO instructions.
The programmer can directly access any memory location directly. To prevent such an access, the OS (kernel) will divide the address space into kernel space and user space. An user application can easily access user application. To access kernel space, we need system calls (traps).
Q 55. Which UNIX/Linux command is used to make all files and sub-directories in the directory “progs” executable by all users ?
(A) chmod− R a+x progs
(B) chmod −R 222 progs
(C) chmod−X a+x progs
(D) chmod −X 222 progs
Answer : (A) chmod− R a+x progs
Solution : Option A will make all files and sub-directories in the directory (progs) executable by all users.
-R is for recurssive calls, so that sub-directories within the directories can be accessed.
a is for all users
+x is for making things executable
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