x86_64 a x86 или x64?

lshw (аппаратное обеспечение списка) с sudo, -Class memory:

sudo lshw -C memory
[sudo] password for stefan: 
  *-firmware              
       description: BIOS
       vendor: American Megatrends Inc.
       physical id: 0
       version: 0208 (01/31/2005)
       size: 64KiB
       capacity: 448KiB
       capabilities: isa pci pcmcia pnp apm upgrade shadowing escd cdboot bootselect socketedrom edd int13floppy1200 int13floppy720 int13floppy2880 int5printscreen int9keyboard int14serial int17printer int10video acpi usb agp ls120boot zipboot biosbootspecification netboot
  *-cache:0
       description: L1 cache
       physical id: 5
       slot: L1-Cache
       size: 32KiB
       capacity: 32KiB
       capabilities: pipeline-burst internal varies data
  *-cache:1
       description: L2 cache
       physical id: 6
       slot: L2-Cache
       size: 2MiB
       capacity: 2MiB
       capabilities: pipeline-burst internal varies unified
  *-memory
       description: System Memory
       physical id: 1b
       slot: System board or motherboard
       size: 1GiB
       capacity: 3GiB
     *-bank:0
          description: DIMM SDRAM Synchronous
          product: PartNum0
          vendor: Manufacturer0
          physical id: 0
          serial: SerNum0
          slot: DIMM0
          size: 512MiB
          width: 64 bits
     *-bank:1
          description: DIMM SDRAM Synchronous
          product: PartNum1
          vendor: Manufacturer1
          physical id: 1
          serial: SerNum1
          slot: DIMM1
          size: 512MiB
          width: 64 bits

Часть:

   size: 1GiB
   capacity: 3GiB

- это то, что вы ищете. Моя система имеет 1GiB, но возьмет 3.