why is minecraft so laggy?!

[gravitate]

i cant bear my PC anymore! when i try to open skylands(info about skylands mod for minecraft here:http://skylands.goonygoon.com/), it gets stuck and barley even moves! i have a windows XP pro, and it is full of crap, and i'm waiting for my new PC. i am already using game booster, but it doesn't help.i have the highest fog on, and fast graphics, and nothing happens. can you help me out?

 

[rokkolpo]

Obviously we have the same computer xD

 

[Blaster395]

1. The newest minecraft update added some lighting areas that happen if you have no bedrock anywhere in the map, as in, map made entirely out of floating islands will cause lag.
2. In order to play minecraft at a reasonable framerate you should have a decent Graphics card, laptops and low end PCs often do not have Graphics cards, and only have integrated GPUs.

 

[Diligent]

It's also still in alpha, so I wonder if it will be optimized a little more.

 

[Sephychu]

Wait;
"My laptop is old and full of crap..."
"Why is Minecraft so laggy?"

Answered your own question there, man.