Developers have got their sticky mitts on a build of iPad iOS 4.2, and have discovered several improvements and enhancements that weren't talked about at its unveiling.

For starters, the screen orientation lock, which stops the iPad from switching from vertical to horizontal view on when rotating the device, is now a volume mute button. Instead, when users want to lock the screen in place, they need to access the new multitasking bar, swipe to the left, and select a dedicated mode. reports that there is also now a brightness slider, which stops users having to go into the settings mode just to darken or brighten the screen. However, so far, this option is only available in iBooks and the development kit has no option for third-party programmers to implement it.

The same system for registering 3G signal bars as the iPhone 4 (after 4.0.1) is now in evidence. And folders on the iPad can hold up to 20 applications each, in preference to the 12 on the iPhone and iPod touch.

Fonts in Notes can now be changed (to Helvetica and Chalkboard), and Cnet's final revelation is that the YouTube app now sports the thumbs up / thumbs down rating method to bring into line with the online site.

There are probably plenty of other minor changes, especially in individual applications. Pocket-lint can't wait to find them out. Unfortunately, the consumer build of iOS 4.2 is not due until November.

Don't forget to check out the major changes coming in iPad iOS 4.2 too.

And let us know what you think about them, and the iPad generally, in the comments below...