Memory Management

Question 1

Swapping

Answer 1

Processes swapped temporarily to a back store then brought back to memory for execution

Question 2

Advantages of swapping

Answer 2

Increases degree of multiprogramming in a system

Question 3

Contiguous allocation

Answer 3

Way of organizing program in memory where a program must exist as Contiguous adddreses

Question 4

Compaction

Answer 4

Shuffle memory contents to place all free memory together in one large block (only when allocation is dynamic)

Question 5

Requirements of Primary Memory

Answer 5

• The primary memory access time must be as small as possible
• The primary memory must be as large as possible
• The primary memory must be cost effective

Question 6

Protection of memory space

Answer 6

Protection by using a pair of base and limit registers define the logical address space of a process

Question 7

Hardware Address Protection

Answer 7

CPU must check every memory access generated in user mode to
be sure it is between base and limit for that user

Question 8

Address Binding

Answer 8

Mapping and loading instructions and data to locations in RAM (main memory)

Question 9

Address binding of instructions and data to memory addresses can
happen at three different stages, what are they?

Answer 9

• Compile time: If memory location known a priori, absolute code can be generated; must recompile code if starting location changes
• Load time: Must generate relocatable code if memory location is not known at compile time
• Execution time: Binding delayed until run time if the process can be moved during its execution from one memory segment to another

Question 10

Logical vs. Physical Address Space

Answer 10

• Logical address – generated by the CPU; also referred to as virtual address
• Physical address – address seen by the memory unit
  *Logical and physical addresses are the same in compile-time and load time address-binding schemes; logical (virtual) and physical addresses differ in execution-time address-binding scheme

Question 11

Logical address space

Answer 11

Is the set of all logical addresses generated
by a program

Question 12

Physical address space

Answer 12

Is the set of all physical addresses
generated by a program

Question 13

Memory-Management Unit (MMU)

Answer 13

Hardware device that at run-time maps virtual to physical address

Question 14

Fixed-Partition Strategy

Answer 14

Divide memory into N fixed size regions,
possibly of different sizes

Question 15

Internal Fragmentation

Answer 15

• Memory allocated to one process may be more than what it needs
• Memory allocated to one process cannot be used by another, even if it is unused

Question 16

Variable-Partition Strategy

Answer 16

Allocate a process exactly what it
needs

Question 17

External Fragmentation

Answer 17

• As system runs, memory may be fragmented between processes
• The unused memory does not belong to any of the processes surrounding it
• Total memory space may exist to satisfy a request, but it is not contiguous