Diff between low voltage pentium M and pentium M

I am considering purchasing a Dell X300 notebook computer. As Dell has
specified, it has a "Low voltage Intel Pentium M processor". Other
models have a "Intel Pentium M processor". My questions are:

(1) What is the difference between a "Low voltage Pentium M processor"
and a "Pentium M processor"?
(2) For the same clock speed, how much performance is reduced for a
"low voltage pentium M" as compared to a "Pentium M"?

Any relevant comments and information are appreciated.

Sam Yang