Q. In the IBM/370 memory protection is offered through the use of keys. A key is a 4-bit quantity every 2K block of memory has a key (the storage key) associated with it. The CPU as well has a key (the protection key) associated with it. A store operation is permitted only if both keys are equal or if either is zero. Which of the subsequent memory-management schemes could be used successfully with this hardware?

a. Bare machine

b. Single-user system

c. A Multiprogramming with a fixed number of processes

d. A Multiprogramming with a variable number of processes

e. Paging

f. Segmentation

Answer:

a. Protection not necessary set system key to 0.

b. Set system key to 0 when in supervisor mode.

c. Region sizes should be fixed in increments of 2k bytes allocate key with memory blocks.

d. Same as above.

e. Frame sizes should be in increments of 2k bytes, allocate key with pages.

f. Segment sizes should be in increments of 2k bytes, allocate key with segments.