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64bit and x64

64-bit guests

Starting with
Version 2.0, VirtualBox also supports 64-bit guest operating systems.
Starting with Version 2.1, you can even run 64-bit guests on a 32-bit
host operating system, so long as you have sufficient hardware.

In particular, 64-bit guests are supported under the
following conditions:

  1. You
    need a 64-bit processor with hardware virtualization support

  2. You
    must enable hardware virtualization for the particular VM for which you
    want 64-bit support; software virtualization is not supported for
    64-bit VMs.

  3. If you want to use 64-bit guest support on a
    32-bit host operating system, you must also select a 64-bit operating
    system for the particular VM. Since supporting 64 bits on 32-bit hosts
    incurs additional overhead, VirtualBox only enables this support upon
    explicit request.

    On 64-bit hosts, 64-bit guest support is always
    enabled, so you can simply install a 64-bit operating system in the
    guest.

To give a
little more information on that, the X86 processors started with the
Intel 8086 processor way back in 1978. They were incrementally improved
(80186, 80286) and then Intel released the Intel 386 (i386) in 1980.
That was then followed by he 486 (i486), the Pentium (i586), and the
Pentium 3/4 (i686) and AMD

‘s Athlon/Duron/T-bird (also i686).

Since all these processors were based on the same architecture
(basically they read/wrote 1’s and 0’s in the same way), and their names
all contained "86", the whole family was collectively called "X86". All
the X86 processors were 32-bit.

The recent trend has been to move toward 64-bit processors, and several
different architectures popped up. DEC’s Alpha and Motorola’s PPC chips
have been 64-bit for a while, but Intel’s Itanium and Xeon and AMD’s
Athlon64 are the new kids on the block.

The difference between the Itanium and PPC versus the Athlon64 is that
the Itanium and PPC have completely different architectures (they speak
different 1 and 0 languages), whereas the Athlon64 speaks the same
language as the 32-bit X86 processors, but adds 64-bit registers.
Therefore the name of the Athlon64 in generic terms is "X86_64".

Intel, not to be outdone, has since redesigned its 64-bit Xeon
processors to use the same kind of architecture as the Athlon64, calling
it "Intel 64-bit with Extended Memory Technoloty". Basically they
couldn’t say they copied AMD without being laughed at in irony (since
AMD got its start by simply copying Intel’s chips).

uname -a and uname -m
echo $HOSTTYPE

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