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# Thursday, September 23, 2004
/3gb switch and virtual memory

Raymond Chen recently wrote a number of posts about the /3gb switch and virtual memory.

  • The oft-misunderstood /3GB switch. It's simple to explain what it does, but people often misunderstand.
  • Kernel address space consequences of the /3GB switch. An adverse consequence of the /3GB switch.
  • Myth: Without /3GB the total amount of memory that can be allocated across all programs is 2GB. Virtual memory is not virtual address space (part 1).
  • Myth: Without /3GB a single program can't allocate more than 2GB of virtual memory. Virtual memory is not virtual address space (part 2).
  • Myth: You need /3GB if you have more than 2GB of physical memory. Virtual address space is not physical memory.
  • Myth: The /3GB switch expands the user-mode address space of all programs. A program must request it before it gets it.
  • Why does Exchange recommend /3GB if you have more than 1GB of physical memory? Bologna and cheese sandwiches.
  • Myth: The /3GB switch lets me map one giant 3GB block of memory. There are still holes in the virtual address space.
  • Why is the virtual address space 4GB anyway? That's what happens when you have 32-bit pointers.
  • Myth: PAE increases the virtual address space beyond 4GB. PAE is an extension for physical address, not virtual addresses.
  • Myth: In order to use AWE, you must enable PAE. The two are independent. AWE is how programs access physical memory. PAE is how the CPU accesses physical memory.
  • The curious interaction between PAE and NX. NX uses a feature available only in PAE mode.
    • Thursday, September 23, 2004 6:59:27 AM (Pacific Daylight Time, UTC-07:00)  #    Comments [0] - Trackback
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