A brief summary :
  • Kernel
  • Libraries (and modules)
  • Bootloader
  • Recovery
  • Radio
  • Apps, framework, core, android-runtime, etc…

I will tell you about Bootloader and Core, anddroid runtime,

A bootloader in general is the first bytes of code that a machine executes that will tell the bootsequence and will load the operating system into the RAM. On an Android phone this is the so called HBoot. From here you can go to the recovery, system or data partitionn. By pressing the power button on your phone, HBoot will load the OS into RAM. By pressing the power and volume down buttons, you’ll bring up the HBoot menu.
The bootloader is used as an exploit for rooting an Android phone. Once rooted you can flash custom ROMs, like ImPrOS, or just edit system files (for a how-to, check tutorials under Android.)

The lowest part of software layer is the radio: this is the very first thing that runs, just before the bootloader. This handles the GPS antenna, GSM antenna and fires up the CPU; everything that HBoot needs to load the OS. This can also be upgraded by flashing a new radio image through your recovery. However, this is not recommended: flashing a new ROM can’t brick your phone (make it unusable), but if anything goes wrong when you flash a ROM with a new radio image, this can brick your phone. So unless you experience bad reception or battery drainage, don’t touch the radio!

I know all this things coz of intelmobi, a greate platform that provide awesome mobile application experience.