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I like working in 64-bit now on my iMac and the whole system seems to run a bit faster. The problem is holding down the 6 and 4 during every boot. Is there a way to force this into 64-bit all of the time?

I have searched Google some, but most of the options seems like a hack. Which works and which is easiest to back out of if necessary?

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up vote 2 down vote accepted

The safest way is to edit the com.apple.Boot plist, as documented on this page. The file is located at /Library/Preferences/SystemConfiguration/com.apple.Boot.plist. Find the Kernel Flags key and add arch=x86_64:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Kernel</key>
    <string>mach_kernel</string>
    <key>Kernel Flags</key>
    <string>arch=x86_64</string>
</dict>

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