Having just done a simple search on Google, I've found a plethora of websites detailing the key features, benefits and disadvantages and comparison charts between a wide range of Canon EOS models, including the 1DX
Get creative with your search terms on Google (or any other search engine for that matter) and you'll have all the information you could possibly need within minutes.
Why not start with this? Wikipedia Canon EOS Comparison Chart
To please those that feel my response wasn't adequate, here are the key features.
Key features of the Canon EOS 1D X
- 18.1 MP full frame CMOS sensor
- Up to 12fps plus 14fps High speed mode
- 100-51200 ISO, up to H:204800
- 61 point AF system
- Full HD 1080p EOS movie
- Dual “DIGIC 5+” processors
- Clear View II 8.11 cm (3.2”) 1,040k LCD
- Ethernet port
- Lens compatibility: As this camera features a full-frame sensor it can only take Canon's EF, Sigma's DG and Tamron's Di lenses. The EOS 1D X is not compatible with Sigma's DC, Tamron's Di II or Canon's EF-S lenses.
Here are the benefits of some of the features listed above
18.1 MP full frame CMOS sensor
A Canon 18.1 MP full frame CMOS sensor delivers stunning performance, producing exceptional low noise, high-resolution images even in the darkest conditions. The full frame sensor delivers optimum results from wide-angle lenses and gives you greater control over depth of field. Image resolution exceeds the quality demanded by leading photo agencies - making it ideal for extra large prints up to A2 size, even after cropping.
Super high speed shooting
Capture every second of the action with up to 12fps continuous shooting, increasing to an incredible 14fps in Super High speed shooting with continuous bursts of up to 120 large JPEG images (36 RAW).
Huge ISO range
An exceptionally wide ISO range of 100 to 51200 – expandable up to an incredible ISO 204800 – means shooting need never stop from the brightest conditions right through to near darkness.
61 point AF system
A high-precision 61 point AF system, featuring 41 high sensitivity cross type sensors, delivers fast, accurate focussing of fast moving subjects – whatever the lighting conditions. The centre 5 AF points are dual cross type for added precision.
Consistent, accurate metering
A 100,000 pixel RGB AE metering system with a dedicated DIGIC 4 processor measures not only brightness but also colour to ensure highly accurate exposure for natural results even in complex lighting situations.
Full HD EOS movies
Shoot Full HD (1080p) video with a wide range of user selectable controls on a DSLR including exposure, frame rates, audio and compression control. An HDMI output allows High Definition playback of footage and images.
Dual “DIGIC 5+” processors
Canon’s latest generation Dual “DIGIC 5+” processors deliver the fastest and most advanced image processing to date for best-in-class image quality. Working with 4 A/D converters to provide 14-bit image processing for smooth tonal gradations and natural looking colours as well as advanced Noise Reduction at higher ISO speeds.
Large, anti-reflective LCD
A high-resolution 1,040k-dot 3.2” Clear View II LCD screen, allows easy, accurate review of images and video. Superbly durable, an anti-reflective, hardened glass structure prevents reflections even in the brightest sunlight.
Designed for professionals
The EOS-1D X offers a carefully revised version of the classic EOS-1 series design, with larger, more tactile buttons that make it easier for users to control settings – even in extreme conditions where gloves are required. Two multi-controllers and a touch-sensitive control wheel, for use in movie mode, make it easier to change settings, while a range of customisable function buttons allow users to set-up the camera to suit their individual needs by allowing shortcuts to the features and pre-sets they use most.
Built to last
The EOS-1D X offers a highly durable body constructed from high-grade magnesium alloy that provides protection against both the elements and the knocks of everyday use. The latest implementation of Canon’s EOS Integrated Cleaning System also uses technology adopted from Canon lenses, using wave-based vibrations similar to that of Ultrasonic Motors to shake dust and dirt from the sensor even more effectively. An enhanced shutter mechanism also provides extended durability, providing 400K shutter cycles so photographers can rely on their camera to meet the challenge of repeated, demanding shoots. The EOS-1D X also features Canon’s protective sealing around the controls and cover seams, making the camera dust and water-resistant when combined with Canon’s range of weather-resistant EF lenses – perfect for shooting in a range of weather conditions.
A built in Ethernet port allows for fast, easy transfer of images directly to a PC or via a network to clients from live events.
(Information taken directly from Canon and their specification sheets and product data)