FACTOID # 27: If you're itching to live in a trailer park, hitch up your home and head to South Carolina, where a whopping 18% of residences are mobile homes.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
   
 
WHAT'S NEW
RELATED ARTICLES
People who viewed "EM64T" also viewed:
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > EM64T

Extended Memory 64-bit Technology (EM64T) is Intel's implementation of AMD64, a 64-bit extension to the IA-32 architecture. See the AMD64 article for architectural details. Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... AMD64 Logo AMD64 (also x86-64 or x64) is a 64-bit microprocessor architecture and corresponding instruction set designed by Advanced Micro Devices. ... In computing, a 64-bit component is one in which data are processed or stored in 64-bit units (words). ... It has been suggested that this article or section be merged with X86 assembly language. ... AMD64 Logo AMD64 (also x86-64 or x64) is a 64-bit microprocessor architecture and corresponding instruction set designed by Advanced Micro Devices. ...


From the Intel Website:


"Intel EM64T improves performance by allowing the system to address more than 4 GB of both virtual and physical memory. Intel EM64T provides support for:

  • 64-bit flat virtual address space
  • 64-bit pointers
  • 64-bit wide general purpose registers
  • 64-bit integer support
  • Up to 1 terabyte (TB) of platform address space"

Contents


Intel CPUs with EM64T

EM64T was originally implemented on the E revision (Prescott) of Pentium 4 line of microprocessors, which were supported by i915P (Grantsdale) and i925X (Alderwood) chipsets in June of 2004. EM64T's implementation was largely due to the competitive pressure of Advanced Micro Devices AMD64 technology implemented on Opteron and Athlon64 lines of microprocessing units, otherwise known as the K8 core, one year earlier in 2003; and the technology was largely built compatible to AMD64, and the then announced Windows XP 64 bit Edition supporting AMD64 technology. Intel's first processor to activate the EM64T technology was the multi-socket processor Xeon codenamed Nocona. Since the Xeon itself is directly based on Intel's desktop processor, the Pentium 4, the Pentium 4 also has EM64T technology built in, although as with Hyper-Threading, this feature was not initially enabled on the then-new Prescott design, likely because enabling EM64T didn't coincide with Intel's stance on x86-64 extensions at that particular time. Intel has since begun selling EM64T enabled Pentium 4s using the E0 revision of the Prescott core, being sold on the market as the Pentium 4, model F. However, the revision F core was targeted at workstations. Intel's official launch of EM64T to desktop was the N0 Stepping Prescott-2M. The E0 revision also adds eXecute Disable(XD) support to EM64T, Intel's name for the NX bit, and has been included in the current Xeon codenamed Irwindale. All 9xx/8xx/6xx/5x6/5x1/3x6/3x1 series CPUs have EM64T enabled, as will all future Intel CPUs. For other possible meanings of AMD see AMD (disambiguation) Advanced Micro Devices, Inc. ... AMD64 Logo AMD64 (also x86-64 or x64) is a 64-bit microprocessor architecture and corresponding instruction set designed by Advanced Micro Devices. ... The AMD Opteron is the first eighth-generation x86 processor (K8 core), and the first of AMDs AMD64 (x86-64) processors, released April 22, 2003. ... This article or section should include material from Athlon The Athlon 64 (codenamed ClawHammer and Newcastle) represents AMDs entry into the consumer 64-bit microprocessor market, released on September 23rd, 2003. ... AMD64 Logo AMD64 (also x86-64 or x64) is a 64-bit microprocessor architecture and corresponding instruction set designed by Advanced Micro Devices. ... Xeon logo The Xeon is Intels name for its server-class PC microprocessors intended for multiple-processor machines. ... New Intel Pentium 4 with Hyper Threading logo The Pentium 4 is a seventh-generation x86 architecture microprocessor produced by Intel and is their first all-new CPU design, called the NetBurst architecture, since the Pentium Pro of 1995. ... Hyper-Threading (HTT = Hyper Threading Technology) is Intels trademark for their implementation of the simultaneous multithreading technology on the Pentium 4 microarchitecture. ... New Intel Pentium 4 with Hyper Threading logo The Pentium 4 is a seventh-generation x86 architecture microprocessor produced by Intel and is their first all-new CPU design, called the NetBurst architecture, since the Pentium Pro of 1995. ... NX stands for No eXecute. ...


As of March 2006, none of Intel's notebook CPUs (Core Duo, Pentium M, Celeron M, Mobile Pentium 4) support EM64T. The first Intel mobile processor supporting EM64T will be the dual core Merom version of the Core 2 processor, which is scheduled to be released in August 2006. It has been suggested that this article or section be merged into Intel Core. ... Introduced in March 2003, the Pentium M is an x86 architecture microprocessor designed and manufactured by Intel. ... 633MHz Celeron A Celeron is any of a large number of different budget x86 microprocessors produced by Intel and marketed as a budget/value CPU line. ... New Intel Pentium 4 with Hyper Threading logo The Pentium 4 is a seventh-generation x86 architecture microprocessor produced by Intel and is their first all-new CPU design, called the NetBurst architecture, since the Pentium Pro of 1995. ... Core 2 Duo brand logo This article is about Intel processors branded as Intel Core 2. ...


Differences between AMD64 and EM64T

There are a small number of differences between each instruction set. Compilers generally produce binaries that target both AMD64 and EM64T, making the differences mainly of interest to compiler developers and operating system developers.

  • Early AMD64 processors lacked the CMPXCHG16B instruction, which is an extension of the CMPXCHG8B instruction present on most post-486 processors. Similar to CMPXCHG8B, CMPXCHG16B allows for atomic operations on 128-bit double quadword (or oword) data types. This is useful for high resolution counters that could be updated by multiple processors (or cores). Without CMPXCHG16B the only way to perform such an operation is by using a critical section.
  • Early Intel CPUs with EM64T lacked LAHF and SAHF instructions supported by AMD64 until introduction of Pentium 4 G1 step in December 2005. LAHF and SAHF are load/store instructions for certain status flags. As the only real purpose of these instructions was to enable quick porting of Intel 8080 code to the Intel 8086 in the late 1970s, this limitation is of little consequence now.
  • Early Intel CPUs with EM64T also lack the NX bit (No Execute bit) of the AMD64 architecture. The NX bit marks memory pages as non-executable, allowing protection against many types of malicious code.
  • SYSCALL and SYSRET are also only supported in IA-32e mode (not in compatibility mode) on EM64T. SYSENTER and SYSEXIT are supported in both modes.
  • Near branches with the 0x66 (operand size) prefix behave differently. One type of CPU clears only the top 32 bits, while the other type clears the top 48 bits.
  • EM64T's BSF and BSR instructions act differently when the source is 0 and the operand size is 32. The processor sets the zero flag and leaves the upper 32 bits of the destination undefined.
  • AMD64 supports 3DNow! instructions. This includes prefetch with the opcode 0x0F 0x0D and PREFETCHW, which are useful for hiding memory latency.
  • EM64T lacks the ability to save and restore a reduced (and thus faster) version of the floating-point state (involving the FXSAVE and FXRSTOR instructions).
  • EM64T lacks some model-specific registers that are considered architectural to AMD64. These include SYSCFG, TOP_MEM, and TOP_MEM2.
  • EM64T supports microcode update as in 32-bit mode, although it has been rumored that AMD processors have supported programmable microcode (an undocumented feature) for years.
  • EM64T's CPUID instruction is very vendor-specific, as is normal for x86-style processors.
  • The MONITOR and MWAIT instructions, used by operating systems to better deal with Hyper-threading, are only supported (and only useful) on EM64T.
  • AMD64 systems allow the use of the AGP aperture as an IO-MMU. Operating systems can take advantage of this to let normal PCI devices DMA to memory above 4 GB. EM64T systems require the use of bounce buffers, which are slower.
  • Originally EM64T hardware allowed access only to 236 bytes of memory, while AMD64 systems can handle up to 240 (planned expansion to 256) bytes. However, as of recent publications, EM64T now provides 240 bytes of memory access.

// Overview The exposed die of an Intel 80486DX2 microprocessor. ... In computer science, an atomic operation is an operation during which a processor can simultaneously read a location and write it in the same bus operation. ... In computer programming a critical section is a piece of code that can only be executed by one process or thread at a time. ... Intel C8080A processor. ... It has been suggested that Microprocessor 8086 be merged into this article or section. ... NX stands for No eXecute. ... The first 3DNow! CPU 3DNow! is the name of a multimedia extension created by AMD for its processors, starting with the K6-2 in 1998. ... RAM Latency is the amount of wait time that a computer experiences when trying to access data in its RAM. RAM latency is measured in front side bus clock cycles. ... For the IEEE binary floating-point standard, see its page. ... A microprogram is a program consisting of microcode that controls the different parts of a computers central processing unit (CPU). ... Hyper-Threading (HTT = Hyper Threading Technology) is Intels trademark for their implementation of the simultaneous multithreading technology on the Pentium 4 microarchitecture. ...

See also

In computing, a 64-bit component is one in which data are processed or stored in 64-bit units (words). ... AMD64 Logo AMD64 (also x86-64 or x64) is a 64-bit microprocessor architecture and corresponding instruction set designed by Advanced Micro Devices. ... In computing, IA-64 (or ia64, short for Intel Architecture-64) is a 64-bit processor architecture developed in cooperation by Intel and Hewlett-Packard, implemented by processors such as Itanium and Itanium 2. ...

External links

  • Intel Extended Memory 64 Technology
  • Intel tweaks EM64T for full AMD64 compatibility
  • Early report of differences between Intel IA32e and AMD64
  • Analyst: Intel Reverse-Engineered AMD64

  Results from FactBites:
 
EM64T - Wikipedia, the free encyclopedia (788 words)
EM64T was originally implemented on the E revision (Prescott) of Pentium 4 line of microprocessors, which were supported by i915P (Grantsdale) and i925X (Alderwood) chipsets in June of 2004.
EM64T lacks the ability to save and restore a reduced (and thus faster) version of the floating-point state (involving the FXSAVE and FXRSTOR instructions).
EM64T supports microcode update as in 32-bit mode, although it has been rumored that AMD processors have supported programmable microcode (an undocumented feature) for years.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m