20
IBM System x3950 M2 and x3850 M2 Technical Introduction
A quad-pumped 266 MHz bus therefore results in a 1066 MHz front-side bus.
The bus is eight bytes wide, which means it has an effective burst throughput of
8.53 GBps. This can have a substantial impact, especially on TCP/IP-based LAN traffic.
Intel 64 Technology (formerly known as EM64T)
First introduced in the Xeon DP Nocona processor, Intel 64 Technology is a 64-bit
extension to the industry standard IA32 32-bit architecture. Intel 64 Technology adds:
– A set of new 64-bit general purpose registers (GPR)
– 64-bit instruction pointers
– The ability to process data in 64-bit chunks
Even though the names of these extensions suggest that the improvements are simply in
memory addressability, Intel 64 Technology is, in fact, a fully functional 64-bit processor.
The Tigerton
processors limit memory addressability to 40 bits of addressing.
There are three distinct operation modes available in Intel 64 Technology:
– 32-bit legacy mode
The first and, in the near future, probably most widely used mode will be the
32-bit
legacy mode
. In this mode, processors with Intel 64 Technology will act just like any
other IA32-compatible processor. You can install your 32-bit operating system on such
a system and run 32-bit applications, but you will not be able to make use of the new
features such as the flat memory addressing above 4 GB or the additional General
Purpose Registers (GPRs). 32-bit applications will run just as fast as they would on any
current 32-bit processor.
Most of the time, IA32 applications will run even faster because there are numerous
other improvements that boost performance regardless of the maximum address size.
– Compatibility mode
The second mode supported by Intel 64 Technology is the
compatibility mode
, which
is an intermediate mode of the full 64-bit mode described in the following list item. To
run in compatibility mode, you will need to install a 64-bit operating system and 64-bit
drivers. If a 64-bit OS and drivers are installed, the processor will be enabled to support
both 32-bit applications and 64-bit applications.
The compatibility mode gives you the ability to run a 64-bit operating system, while still
being able to run unmodified 32-bit applications. Each 32-bit application will still be
limited to a maximum of 4 GB of physical memory. However, the 4 GB limit is now
imposed on a per-process level, not on a system-wide level. This means that every
32-bit process on this system gets its very own 4 GB of physical memory space,
provided sufficient physical memory is installed. This is already a huge improvement
compared to IA32, where the operating system kernel and the application had to share
4 GB of physical memory.
Additionally, the compatibility mode does not support the virtual 8086 mode, so
real-mode legacy applications are not supported. 16-bit protected mode applications,
however, are supported.
– Full 64-bit mode
The final mode is the
full 64-bit mode
. Intel refers to it as the
IA-32e mode
. (For
AMD™, it is the
long mode
). This mode is applied when a 64-bit OS and 64-bit
application are used.
In the full 64-bit operating mode, an application can have a virtual address space of up
to 40 bits, equating to one terabyte (TB) of addressable memory. The amount of
physical memory will be determined by how many DIMM slots the server has and the
maximum DIMM capacity supported and available at the time.
