A different examination is taken for each area of study, but school students are usually obliged to take examinations for certain "core subjects" (English language, English literature, mathematics, and science) along with several optional subjects; sometimes up to 10-14 in total. There is also an option for students to take "short" or "half" courses for certain subjects.
There are different tiers for most examination - normally "foundation" and "higher", and for some subjects, "intermediate". Students are entered for a certain tier based on their ability. The tier a student is entered for affects the range of grades that student could attain.
Some subjects, such as science, can be split up into several different subjects: it is possible to be examined on science as a whole, or biology, chemistry and/or physics separately.
It was introduced in 1988, and replaced both the O-level GCE (Ordinary level General Certificate of Education) and the CSE (Certificate of Secondary Education) qualifications.
Some commentators feel that the GCSE system is a dumbing down from the old GCE / O Level system, joking that it stands for Get Cretins Some Exams.
Recently introduced is the VGCSE system, the "V" meaning "vocational," which points courses to the business and "applied knowledge" side of courses. VGCSE courses now include ICT and Manufacturing, amongst others.
GCSE (global common subexpression elimination) is an optimisation technique used by some compilers - e.g., gcc implements it.