In each case, only one change is listed in the release notes for the firmware. For the Nikon S4000 firmware v1.1, the company has boosted the high definition 720p (1,280 x 720 pixel) video mode frame rate from 24 to 30 frames per second. Nikon S640 v1.2, meanwhile, corrects a rare issue whereby images shot with digital zoom enabled weren't recorded correctly.

Announced last August, the Nikon Coolpix S640 is priced at $250. The Coolpix S640 couples a twelve megapixel CCD image sensor to a Nikkor-branded optically-stabilized 5x zoom lens with 28mm wide angle. The Nikon S640's display is a run-of-the-mill 2.7-inch LCD with 230,000 dot resolution. The Nikon S640's selling point is its speed -- at launch, Nikon claimed its 0.7-second startup time as the fastest of any 5x zoom compact camera featuring optical image stabilization. The S640 was also described as yielding the fastest autofocusing in a Coolpix camera, with a 0.39 second shutter lag. The Nikon Coolpix S640 stores images and videos in 45MB of built-in memory or on Secure Digital media, and draws power from a proprietary Lithium Ion battery. More details can be found in our Nikon S640 preview.

Announced in February 2010, the Coolpix S4000 features an effective resolution of twelve megapixels, and a 4x optical zoom lens with a useful 27mm wide angle. The Nikon S4000 doesn't include any form of mechanical image stabilization, instead relying on software techniques to combat blur from camera shake. The S4000 provides a 3.0-inch LCD on which to frame and review images and movies. Data is stored on SD or SDHC cards, or in 45MB of built in memory. Power for the Nikon S4000 comes courtesy of a proprietary lithium-ion battery, rated as good for 190 shots on a charge. The Nikon Coolpix S4000 also offers USB 2.0 High Speed data connectivity. The Coolpix S4000 is priced at around $200. For more details, read our Nikon S4000 preview.

The firmware for each camera can be downloaded from Nikon's website, on the Coolpix S640 v1.2 firmware and Coolpix S4000 v1.1 firmware download pages respectively.