With the latest season of 'Doctor Who' ending, you'll have the rest of the summer to catch up on your 'Who' history. If you're a purist, the best way to do that is to go back to the vaults and watch the show.

BBC America just released four more volumes, covering the First Doctor (William Hartnell, 1963-1966), the Third Doctor (Jon Pertwee, 1970-1974), and the Fourth Doctor (Tom Baker, 1974-1981).

More than two thirds of the episodes are available on DVD, and the BBC plans to eventually release everything it has. Mind you, some of the earliest episodes from the '60s and '70s were erased to make way for newer programs, but bits of those turn up here and there.

The most recent additions give a decent overview of three of the first four Doctors, and the first two decades of the show. The BBC releases the older episodes in collections representing story arcs, rather than by season, the way we're most used to seeing TV on DVD. They can be a bit pricey, but you can get a bunch of them through Netflix, and sometimes, even the local library.

Here's what you get with the latest collections:

The William Hartnell Years 1963-1966
'The Space Museum' and 'The Chase'
This is a three-disc set with two full story arcs, plus a lot of fine extras. In 'The Space Museum' the Doctor and his companions (there were always companions) find themselves preserved in a museum, wondering whether they should fight their way out. There's a lot of humor here, and the cheesy costumes and uneven acting are typical of the production at its start. Some of the extras on the DVDs feature evaluations of the episodes, and many, like 'Defending the Museum' here, are pretty frank discussing the shortcomings.

You also get 'The Chase,' an early appearance by the Daleks, who had already been established as the Doctor's greatest enemy. Perhaps the most amazing thing about this, and the extras that touch on monster design, is how little the Daleks have changed in more than 45 years of Doctor Who. They still have the bulky, upside-down garbage can with a plunger hanging off a dome head, and they have retained the voice - "Exterminate!" The main difference is that the versions the Eleventh Doctor faces have gotten shiny new multi-colored iPod skins.

The Jon Pertwee Years 1970-1974
'The Time Monster'
The Doctor battles The Master, who is attempting to gain control of time while undercover at a lab in Cambridge University. This episode also gives some insight into the mystery of Atlantis (a crack in time, "between now... and now"). The Master figured prominently into 'The End of Time,' the episodes that led to the end of David Tennant's Tenth Doctor and made way for Matt Smith as the Eleventh Doctor.

As always, The Master is power mad and brilliant, and a good foil for the Doctor. The production and writing of this arc are a step up from the previous seasons - this looks more like the classic series fans are most familiar with. Science nerds will enjoy the DVD extra explaining the science behind 'The Time Monster' and the concept of interstitial time with Professor Jim Al Khalili.



The Tom Baker Years 1974-1981
'Underworld'
The Doctor aids a race called the Minyans who are on a quest to find a new home, at drift in space after their planet was destroyed. Of course, the Time Lords tried to help them in the distant past, when the Minyans mistook them for gods. At least one Minyan blames the Time Lords for the destruction of the planet.

A great self-aware sense of humor in this arc, something fans of Smith and Tennant will enjoy. One of the Minyans asks the Doctor if he has any idea how painful it is to regenerate. He replies he's been through it a couple of times, and didn't find it pleasant. And when the Doctor introduces himself by name, that same Minyan asks, "Of medicine?" "Oh, many things," the Doctor says offhandedly.

You also get to see the dog-like K-9, who had his own spinoff series at one point. You can see K-9 again putting up a valiant fight in 'School Reunion,' season two, episode three of the modern series.

For an understanding of the show's continuing budget challenges with the BBC, see the 'Making of' DVD extra.

The Tom Baker Years 1974-1981
'The Horns of Nimon'
The TARDIS is a fickle machine, whether it's the Eleventh Doctor working the antique knobs of the Fourth Doctor trying to make sense of a giant instruction manual. The Doctor has to struggle with getting the TARDIS up and running while trying to prevent the parasitic Nimon from securing their latest sacrifices and moving on to destroy other worlds. In fact, the Doctor does a lot of fixing in this story. And there is an appearance by the sonic screwdriver.

This is Baker's second to last story in his second to last season, and the budget constraints once again show in some scenes, especially when an asteroid is heading straight for the TARDIS and the mask design of the Nimon. Much paper mache was constructed.

Some great detail in the extras, including a featurette on 'Doctor Who' and the children's show 'Blue Peter,' an interview with writer Anthony Read, and even some music demos from Peter Howell. Read talks about 'Hitchhikers Guide to the Galaxy' writer Douglas Adams' involvement with the show, and the idea that Romana, the Doctor's companion in this arc, was his intellectual equal.