Swapping: Swapping is a process of memory management where processes which are usually idle are stored in the disk. When there is a requirement these processes are swapped from the disk to the memory and then again they are stored in the disk.
Memory compaction: Swapping creates multiple fragments in the memory because of the processes moving in and out. Memory compaction refers to combining all the empty spaces together and then combining all the processes together. The disadvantage of memory compaction is that it requires too much of CPU time.
Memory management using bitmaps: By using bitmaps memory is split in to allocation units. These allocation units can be small or large as per the requirements. For every allocation unit there is a bit in bitmap. Bit is 0 if allocation unit is free and 1 if it is occupied. Size of the allocation unit is inversely proportional to the bitmap. For Example, if allocation unit is large then, bitmap required will be small. Disadvantage of memory management by bitmaps is that it takes a lot of time to search a bitmap.