Specifications

Computer Architecture and Maintenance (G-Scheme-2014)

Processors with 64-bit extension technology can run in real (8086) mode, IA-32

mode, or IA-32e mode. IA-32 mode enables the processor to run in protected mode and

virtual real mode. IA-32e mode allows the processor to run in 64-bit mode and

compatibility mode, which means you can run both 64-bit and 32-bit applications

simultaneously. IA-32e mode includes two submodes:

• 64-bit mode—Enables a 64-bit OS to run 64-bit applications

• Compatibility mode—Enables a 64-bit OS to run most existing 32-bit software

IA-32e 64-bit mode is enabled by loading a 64-bit OS and is used by 64-bit

applications. In the 64-bit submode, the following new features are available:

• 64-bit linear memory addressing

• Physical memory support beyond 4GB (limited by the specific processor)

• Eight new general-purpose registers (GPRs)

• Eight new registers for streaming SIMD extensions (MMX, SSE, SSE2, and SSE3)

• 64-bit-wide GPRs and instruction pointers

IE-32e compatibility mode enables 32-bit and 16-bit applications to run under a 64-

bit OS. Unfortunately, legacy 16-bit programs that run in virtual real mode (that is,

DOS programs) are not supported and will not run, which is likely to be the biggest

problem for many users, especially those that rely on legacy business applications or

like to run very old games. Similar to 64-bit mode, compatibility mode is enabled by

the OS on an individual code basis, which means 64-bit applications running in 64-bit

mode can operate simultaneously with 32-bit applications running in compatibility

mode.

What we need to make all this work is a 64-bit OS and, more importantly, 64-bit

drivers for all our hardware to work under that OS. Although Microsoft released a 64-

bit version of Windows XP, few companies released 64-bit XP drivers. It wasn’t until

Windows Vista and especially Windows 7 x64 versions were released that 64-bit

drivers became plentiful enough that 64-bit hardware support was considered

mainstream.

Note : Microsoft uses the term x64 to refer to processors that support either AMD64 or

EM64T because AMD and Intel’s extensions to the standard IA32 architecture are

practically identical and can be supported with a single version of Windows.

Note: Early versions of EM64T-equipped processors from Intel lacked support for the

LAHF and SAHF instructions used in the AMD64 instruction set. However,Pentium 4

and Xeon DP processors using core steppings G1 and higher completely support these

Prepared By – Prof. Manoj.kavedia (9860174297 – 9324258878 ) (www.kavediasir.yolasite.com)