I own a dell laptop Inspiron/5100. Should I upgrade to a Dell 1505?

Answer:

You forgive me but getting another Dell, regardless of what model it is isn't really an upgrade.

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Getting a Mac would be downgrading.
Go for Inspiron 9400 its better.
You should upgrade to a Mac. You will not be dissapointed. I go from a Dell to a Mac and a Mac is way better contained by every single way... spend the extra bread.