TUTORIAL3

1a)
External Fragmentation: External Fragmentation happens when a dynamic memory allocation algorithm allocates some memory and a small piece is left over that cannot be effectively used. If too much external fragmentation occurs, the amount of usable memory is drastically reduced. Total memory space exists to satisfy a request, but it is not contiguous.
Internal Fragmentation: Internal fragmentation is the space wasted inside of allocated memory blocks because of restriction on the allowed sizes of allocated blocks. Allocated memory may be slightly larger than requested memory; this size difference is memory internal to a partition, but not being used

Of the two types of fragmentation, internal is more predictable than external because the amount of wasted space is determined by the memory allocator’s parameters (how big the allocated blocks must be), which is a constant. In addition, the amount of overall memory lost to internal fragmentation is usually less than what is lost to external fragmentation, although it can gradually accumulate. External fragmentation, on the other hand, is harder to predict because in most cases several processes are regularly starting and stopping in the system and blocks of memory that are used for varying lengths of time are freed up in a different order than they were filled, leaving gaps in the available memory. Therefore, internal fragmentation is more preferred than external fragmentation.

b) In both memory allocation schemes, the PMT tracks page assignments to page frames, but in the paged scheme the PMT is referenced directly from the Job Table, and in segmented/demand paged, it is referenced from the Segment Map Table (SMT), which is referenced from the Job Table.