Hardware Reference
In-Depth Information
Note
Intel began to develop mobile versions of its processors in the early 1990s with the
development of the 386 processor. Both Intel and AMD have developed mobile versions of
almost all of their processors.
Although a mobile processor may have the same code name, a similar model number, and be
based on the same general architecture as its desktop counterpart, it might feature lower clock
speeds, smaller cache sizes, and different implementations of some features. The processor
features for a particular processor family discussed in this chapter apply to desktop
processors. For more information about mobile processors in a given processor family, see the
Intel or AMD websites.
16-Bit to 64-Bit Architecture Evolution
The first major change in processor architecture was the move from the 16-bit internal architecture of
the 286 and earlier processors to the 32-bit internal architecture of the 386 and later chips, which
Intel calls IA-32 (Intel Architecture, 32-bit). Intel's 32-bit architecture dates to 1985. It took a full 10
years for both a partial 32-bit mainstream OS (Windows 95) as well as a full 32-bit OS requiring 32-
bit drivers (Windows NT) to surface, and it took another 6 years for the mainstream to shift to a fully
32-bit environment for the OS and drivers (Windows XP). That's a total of 16 years from the release
of 32-bit computing hardware to the full adoption of 32-bit computing in the mainstream with
supporting software. I'm sure you can appreciate that 16 years is a lifetime in technology.
Now we are near the end of another major architectural jump, as Intel, AMD, and Microsoft have
almost completely shifted from 32-bit to 64-bit architectures. In 2001, Intel had introduced the IA-64
(Intel Architecture, 64-bit) in the form of the Itanium and Itanium 2 processors, but this standard was
something completely new and not an extension of the existing 32-bit technology. IA-64 was
announced in 1994 as a CPU development project with Intel and HP (code-named Merced), and the
first technical details were made available in October 1997.
The fact that the IA-64 architecture is not an extension of IA-32 but is instead a new and completely
different architecture was fine for non-PC environments such as servers (for which IA-64 was
designed), but the PC market has always hinged on backward compatibility. Even though emulating
IA-32 within IA-64 is possible, such emulation and support is slow.
With the door now open, AMD seized this opportunity to develop 64-bit extensions to IA-32, which it
calls AMD64 (originally known as x86-64). Intel eventually released its own set of 64-bit extensions,
which it calls EM64T or IA-32e mode. As it turns out, the Intel extensions are almost identical to the
AMD extensions, meaning they are software compatible. It seemed for the first time that Intel had
unarguably followed AMD's lead in the development of PC architecture.
However, AMD and Intel's 64-bit processor could only run in 32-bit mode on existing operating
systems. To make 64-bit computing a reality, 64-bit OSs and 64-bit drivers are also needed.
Microsoft began providing trial versions of Windows XP Professional x64 Edition (which supports
AMD64 and EM64T) in April 2005, but it wasn't until the release of Windows Vista x64 in 2007 that
64-bit computing would begin to go mainstream. Initially, the lack of 64-bit drivers was a problem,
but by the release of Windows 7 x64 in 2009, most device manufacturers were providing both 32-bit
and 64-bit drivers for virtually all new devices. Linux is also available in 64-bit versions, making the
move to 64-bit computing possible for non-Windows environments as well.
