# Dude, Where's My 4 Gigabytes of RAM?

**URL:** <https://discourse.codinghorror.com/t/dude-wheres-my-4-gigabytes-of-ram/604>\
**Category:** blog\
**Created:** [March 8, 2007, 12:00am UTC](https://discourse.codinghorror.com/t/dude-wheres-my-4-gigabytes-of-ram/604 "2007-03-08T00:00:00Z")\
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**Author:** ![john54](https://discourse-cdn.codinghorror.com/letter_avatar_proxy/v2/letter/j/49beb7/32.png) [@john54](https://discourse.codinghorror.com/u/john54)\
**Post date:** [March 9, 2007, 12:00am UTC](https://discourse.codinghorror.com/t/dude-wheres-my-4-gigabytes-of-ram/604/76 "2007-03-09T00:00:00Z")

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the behavior of the PAE switch on workstation versions of Windows changed beginning with SP2 for XP. Too many drivers were choking when handed addresses outside the 32-bit address range limit and MS was tired of being blamed for the resulting problems, so in SP2 they removed the portion of the PAE switch’s behavior that remapped otherwise-inaccessible RAM below the 4G boundary to above the boundary.

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