1, data size: internal sorting is sorted in memory for datasets that can be stored entirely in memory, while external sorting is sorted on external storage devices for large-scale datasets that cannot be stored entirely in memory.

2. Sorting Algorithms: Internal sorting uses comparative sorting algorithms such as Bubble Sort, Insertion Sort, Selection Sort, Quick Sort, and Normalization Sort. These algorithms sort by comparing the size relationship between data elements. The outer sort uses the merge sort algorithm, which divides the large data set into multiple sub-data sets, sorts each sub-data set in memory, and merges the sorted sub-data sets into the final sorted result.