Service Pack 1a - 3 TYPES! - What's What??

HOwdy all,

I've just been to the Microsoft Download web page and found this

<A HREF="http://www.microsoft.com/downloads/results.aspx?productID=4C937A02-BAE0-4317-A1A9-0C56CD979D05&freetext=Service+Pack&DisplayLang=en" target="_new">http://www.microsoft.com/downloads/results.aspx?productID=4C937A02-BAE0-4317-A1A9-0C56CD979D05&freetext=Service+Pack&DisplayLang=en</A>

There are two things on this page i'm interested in . . .the

"Windows XP Service Pack 1a Checked Network Install (32 bit) for IT Professionals

and the

" Windows XP Service Pack 1a Network Install (32-Bit) for IT Professionals"

WHAT IS THE DIFFERENCE, the Checked one is 20MB bigger????
and why is it called a Cheaked version, whereas the other is not?


and then i find this one:
<A HREF="http://www.microsoft.com/windowsxp/pro/downloads/servicepacks/sp1/network.asp" target="_new">http://www.microsoft.com/windowsxp/pro/downloads/servicepacks/sp1/network.asp</A>

what is this one in comparison to the others???

i'm very curious, and which one should i get?
does it matter?

thanks

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