There hasn't been a movie based on the book. A movie of the same title was made but wasn't about Karellen or the Overlords but about teenage sexuality.
Several people have bought the rights to several of Dr Clarke's stories but nothing has been filmed that I am aware of since 2010, unless you count "Deep Impact" being loosely based on "The Hammer of God". Hope this helps.
Yes, there was a TV mini-series adaptation of "Childhood's End" by Arthur C. Clarke that aired in 2015. It was a three-part series that followed the story of an alien invasion that ushers in a utopian society on Earth.
No. It is an off shoot of the Arthur legend.
The movie 'First Knight' is based of in the legend of King Arthur. It follows a love triangle between Lancelot, Lady Guinevere and King Arthur, and stars Sean Connery and Richard Gere.
Camelot is the name of Arthur's court. It is also the title of a Broadyway musical and of the movie based on the stageplay.
Now and Then
Dudley Moore starred as Arthur in the original movie. Russell Brand starred as Arthur in the 2011 remake.
The novel "Airport" was written by Arthur Hailey. It was first published in 1968 and it inspired the popular disaster film of the same name released in 1970.
King Arthur and the Round Table.
No, HAL is a fictitious computer that appears in the Arthur C. Clark book and Stanley Kubrick movie 2001 a Space Odyssey. No such machine exists nor is one likely to ever exist.
how did the movie start?
Minimoys
The only one that I know of that is entirely about Arthur as a boy is the wonderful Disney animated feature "The Sword in the Stone", based on the book by T.H. White. The very excellent "Excaliber" has an extensive sequence dealing with Arthur's birth and his accession to the throne as a teenager.
Stephen Dillane was Merlin in 2004 movie King Arthur.