motherboard help!?

Question

what are mounted on a laptop's motherboard that are not in a desktop's motherboard??

also, which parts in a laptop motherboard could be upgraded and which parts couldn't be upgraded?

Answer 1

The only thing I can think of that mounted on the Laptop motherboard (MOBO) is a small power supply. Desktops are all in one housing. The MOBO uses a few different voltages; 3V, 5V and 12V. When you use the wall adapter, where you plug into the laptop inside a little board. The wall adapter change 120 volt AC to a 12-17 volt DC and the board inside divides that into the 3, 5 and 12 volts inside +/-.
Parts that may be upgrade easily are Hard Drive, Floppy and CD/DVD player. With the laptop size it may be hard to find a generic brand that fit and you may have to buy from the specific manufacture. The easy way to upgrade is buy USB external drives, modems, Jump-drives etc.
I will get you a link that show an internal upgrade.

Here are some CD/DVD drives;
http://www.directron.com/slimoptical.html

Here some Hard Drives;
http://www.directron.com/nothardrivsata.html

Answer 2

Except for a very few new models, almost every function built into a laptop is on the motherboard.

So on-mobo you will (probably) find:
video adapter
modem
sound card
ethernet card

Sometimes you'll also find the wifi adapter built-on.

Most laptops have (replaceable) mini expansion cards for wifi.

Some laptops have (replaceable) mini expansion cards for network and modem

Very few (and only new & expensive) laptops have (replaceable) mini expansion video cards

Basically, on a laptop if it's built in it's not upgradeable. So on a cheap laptop probably the only thing that can be upgraded is the memory. On more expensive ones you may be able to replace the ethernet or wifi cards (with faster ethernet or wifi cards... there is no backplane for the connectors.
On really expensive laptops you may be able to upgrade the video card.