Microsoft Corp. has unveiled its Surface tablet computer as part of the software company's effort to compete with Apple Inc. and its popular iPad.

The device will hit stores this fall in two models — a lighter, cheaper one with a phone-style processor, and a heavier one with a PC-style Intel processor and the ability to run standard Windows programs. Many details aren't available yet.

Here's how the two Surface models compare with the competition:

— Weight: About 1.5 pounds for the RT version, 2 pounds for the Pro version. Both are heavier than the iPad and other leading competitors. The iPad is 1.44 pounds and Samsung's Galaxy Tab 2 10.1 is 1.24 pounds. Amazon's Kindle Fire and Barnes & Noble's Nook Tablet are both less than a pound.

— Screen size: The display of both Surface models will be 10.6 inches diagonally. That's larger than most rival tablets. The Galaxy is 10.1 inches, while the iPad is 9.7 inches. The Kindle and Nook devices are 7 inches.

— Storage options: 32 or 64 gigabytes for the RT model, 64 or 128 GB for the Pro version. Those are all on the high side. Although the iPad goes up to 64 GB, the standard is 16 GB. The Galaxy also has 16 GB. The Kindle comes with 6 GB, and the Nook comes with 8 or 16 GB.

— Keyboard: Microsoft made a big deal of a removable rubberized keyboard, which also folds over the tablet to act as a cover. The tablet also has a kickstand, which means, combined with the keyboard, it can be set up and used like a small laptop. The Asus Transformer is a popular tablet with a similar concept. A solid keyboard "dock", which also contains an extra battery, attaches to the tablet. The combination folds up like a laptop.

— Expandability: The Surface's storage will be expandable with microSD cards. The Galaxy and the Nook also accept microSD cards, while the iPad and the Kindle don't have slots for more memory.

— USB ports: The RT model will accept USB 2.0 devices, and the Pro version will support the newer USB 3.0. Most tablets, including the iPad, the Galaxy, the Kindle and the Nook, lack ports for connecting USB devices.

Two important things Microsoft didn't specify: how long the Surface's battery lasts on a single charge and the prices the tablets will carry when they hit stores this fall.