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I opened a 31mb .sql file in TEXTEDIT. mostly, just text. took 1-2 minutes to open with a beachball. Everything else in the background ran fine.
 
Exporting a large amount of RAW photos from Aperture converting them to JPEG was a kind of "leave it alone" process. Had Safari, Mail, iCal, iTunes (Playing Music) running as well. while conversions were going I saw allot of beach ball while surfing. never looked at CPU or Mem use.

2011 13" i5 256.
 
I open 127 finder folders all at once last night (by accident) in my mba 1.6ghz core i5, 4gb ram and the mac got hot fast and it kind of froze for 15 minutes.
 
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