M.Sc is the short form of Master of Science, while PGDip is the short form of Postgraduate Diploma. The only similarity between the two is that they are both postgraduate courses in which students are eligible to study after their bachelor's degree. However, their main difference starts with the criteria for the eligibility of each student for these postgraduate courses.
M.Sc is a postgraduate course that a student can study after getting awarded with a bachelor's degree in any science courses. In contrast, PGDip is also a postgraduate course in which students can study after their first degree, regardless of the courses they studied.
Although you are eligible for PGDip after getting awarded with a bachelor's degree in any courses; however, you will still need to pass an exam that will be conducted by your intended school. In contrast, this is not a must in M.Sc. While M.Sc will likely get you a job as a researcher or scientist, PGDip will mostly get you a job as an educator or a trainer.
If in case you are confused about these things, these are for different meanings. MSC stands for Master of Science, which means that someone who has this means that he has already graduated from a 4-year course. Someone who would like to get a PGDip will also need a bachelor’s degree first before he would be eligible to get this postgraduate degree. PGDip stands for Post Graduate Diploma.
Take note that it would take two years before you would be able to complete an MSC while it will take about a year before you can complete the PGDip. The moment that you are done with MSC, this means that you already have all the knowledge needed for different branches of Science. While if you graduate from PGDip, this means that you have learned vital information about some branches of science.