The classic series of Doctor Who was composed of 26 seasons, displayed from November 23, 1963 until December 06, 1989. During the exhibition in the series, each weekly episode was part of a story (or "Arc") - usually compound 4-6 episodes of 25 minutes each, in the last seasons was composed of three 45-minute episodes. Notable exceptions were: "The Daleks Master Plan" (1965-1966), which was exhibited in 12 episodes, the final arc of Season 6, "The War Games" (1969) with 10 episodes and the 23rd Season "The Trial of Time Lord "(1986) had 14 episodes (divided into three code segments narrative production and 4).
Occasionally the seasons have a vaguely related event, these seasons were the 8th Season with Dr. fighting the Master (Lord of the renegade Time and rival of Doctor), the 16th season showing the search for the Doctor and Romana I by Time Key, the 18th season showing the journey of the Doctor and Romana II in E-Space and the 20th Season with the trilogy "Black Guardian".
In 2005 the format of the series changed with each season has 13 episodes of 45 minutes and a Christmas Special 60 minutes. Each season includes several independent stories and two parts connected with a loose story arc that resolves at the end of the season. Some episodes like "Journey's End" (2008), "The Eleventh Hour" (2010) and "Deep Breath" (2014) exceeded the time of 1 hour.
813 episodes of Doctor Who have been televised since 1963, ranging between episodes of 25 minutes (the most common format), episodes of 45 minutes, two full-length productions ("The Five Doctors" (1983) and the film to television in 1996), eight special Christmas (over 60 minutes long, a 72 minutes), and special additional four ranging from 60 to 75 minutes in 2009, 2010 and 2013.
The series began filming in 1080i for HDTV, with the special "Planet of the Dead" (2008), and broadcast live on BBC One and BBC HD.
See also:
Doctor Who
Doctor Who - What is
Doctor Who – The Doctor
Doctor Who - The Story
Doctor Who - How does Sonic Screwdriver
Doctor Who – The Master
Doctor Who - The Companions of Doctor
Doctor Who - The Opponents
Doctor Who - The Seasons
Doctor Who - The Cast of 2005-2014
Doctor Who - Its Production
