The first-generation BMW 1 Series is a compact executive car produced by the German automaker BMW since 2004, when it replaced the BMW 3 Series Compact range as the smallest and least expensive vehicle in the BMW range. As of May 2013, the 3-door and 5-door hatchbacks have been superseded by the F20 and F21 models, while the E82 coupe and E88 convertible variants remain in production.
Available in 3-door hatchback (model code E81), 5-door hatchback (E87), coupe (E82) and 2-door convertible (E88) body styles, the 1 Series features a rear-wheel drive chassis, 50:50 weight balance, longitudinally-mounted engine and aluminum multilink suspension as well as a range of straight-4 straight-6 petrol and diesel engines. The 1 Series accounted for nearly one-fifth of the total sales in 2008
The 1 Series was developed alongside the E90 3 Series. Design work was done by Christopher Chapman in 2001, which was frozen for series production at the end of 2001. The 2002 CS1 Concept previewed the 1-Series design elements at the 2002 Geneva Motor Show.
he 1 Series was launched globally in Autumn 2004 and shares many structural, chassis, powertrain, hardware and electronic elements with the larger E90 3-Series. The model was started to provide a lower point of entry into the BMW range as the 3 Series moved gradually up-market. Initially launched as a five-door hatchback, a three-door version was also launched in July 2007.
The 1 Series Coupé (E82) was unveiled in Internationale Automobil-Ausstellung (IAA) 2007, which went on sale on November 24, 2007.
The 1 Series coupe (E82) and convertible (E88) went on sale in the United States and Canada in model year 2008 (30 June 2007) as the 128i and the 135i. Other countries received the 120i and 125i in both platforms. The convertible, unlike the 3 Series convertible, uses a soft-top instead of a folding hardtop.
The North American introduction of the coupe and cabriolet was during the second quarter of 2008, which was credited for helping BMW overtake Lexus as the top luxury brand.
The first-generation 1 series shares over 60% of components with the E90 3-Series., including front and rear suspension.
In 2011 the E81/87 was replaced by the F20/F21
info from wikipedia.org