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64-620: SSSE3 was first introduced with Intel processors based on the Core microarchitecture on June 26, 2006 with the "Woodcrest" Xeons. SSSE3 has been referred to by the codenames Tejas New Instructions (TNI) or Merom New Instructions (MNI) for the first processor designs intended to support it. SSSE3 has enhanced for HD audio/video decoding/encoding, for example AAC . SSSE3 contains 16 new discrete instructions. Each instruction can act on 64-bit MMX or 128-bit XMM registers. Therefore, Intel's materials refer to 32 new instructions. They include: In

128-425: A 30% performance improvement compared with an otherwise identical, non-simultaneous multithreading Pentium 4. Tom's Hardware states: "In some cases a P4 running at 3.0 GHz with HT on can even beat a P4 running at 3.6 GHz with HT turned off." Intel also claims significant performance improvements with a hyper-threading-enabled Pentium 4 processor in some artificial-intelligence algorithms. Overall

192-432: A 37% decrease. In 2010, ARM said it might include simultaneous multithreading in its future chips; however, this was rejected in favor of their 2012 64-bit design. ARM produced SMT cores in 2018. In 2013, Intel dropped SMT in favor of out-of-order execution for its Silvermont processor cores, as they found this gave better performance with better power efficiency than a lower number of cores with SMT. In 2017, it

256-433: A November 2009 analysis by Intel, performance impacts of hyper-threading result in increased overall latency in case the execution of threads does not result in significant overall throughput gains, which vary by the application. In other words, overall processing latency is significantly increased due to hyper-threading, with the negative effects becoming smaller as there are more simultaneous threads that can effectively use

320-554: A conditional jump would become a single micro-op. However, this technology does not work in 64-bit mode. Core can speculatively execute loads ahead of preceding stores with unknown addresses. Other new technologies include 1 cycle throughput (2 cycles previously) of all 128-bit SSE instructions and a new power saving design. All components will run at minimum speed, raising speed dynamically as needed (similar to AMD's Cool'n'Quiet power-saving technology, and Intel's own SpeedStep technology from earlier mobile processors). This allows

384-463: A different socket in May 2007. The desktop-oriented Conroe began with models having an FSB of 800 MT/s or 1066 MT/s with a 1333 MT/s line officially launched on July 22, 2007. The power use of these processors is very low: average energy use is to be in the 1–2 watt range in ultra low voltage variants, with thermal design powers (TDPs) of 65 watts for Conroe and most Woodcrests, 80 watts for

448-494: A general purpose computer was written by Edward S. Davidson and Leonard. E. Shar in 1973. Denelcor, Inc. introduced multi-threading with the Heterogeneous Element Processor (HEP) in 1982. The HEP pipeline could not hold multiple instructions from the same process. Only one instruction from a given process was allowed to be present in the pipeline at any point in time. Should an instruction from

512-480: A given process block the pipe, instructions from other processes would continue after the pipeline drained. US patent for the technology behind hyper-threading was granted to Kenneth Okin at Sun Microsystems in November 1994. At that time, CMOS process technology was not advanced enough to allow for a cost-effective implementation. Intel implemented hyper-threading on an x86 architecture processor in 2002 with

576-437: A logical processor to borrow resources from a stalled logical core (assuming both logical cores are associated with the same physical core). A processor stalls when it must wait for data it has requested, in order to finish processing the present thread. The degree of benefit seen when using a hyper-threaded, or multi-core, processor depends on the needs of the software, and how well it and the operating system are written to manage

640-419: A malicious thread on a Pentium 4 can use a timing-based side-channel attack to monitor the memory access patterns of another thread with which it shares a cache, allowing the theft of cryptographic information. This is not actually a timing attack , as the malicious thread measures the time of only its own execution. Potential solutions to this include the processor changing its cache eviction strategy or

704-551: A new power delivery feature set specified in Voltage Regulator-Down (VRD) 11.0 . This requirement is a result of Conroe's significantly lower power consumption, compared to the Pentium 4/D CPUs it replaced. A motherboard that has both a supporting chipset and VRD 11 supports Conroe processors, but even then some boards will need an updated BIOS to recognize Conroe's FID (Frequency ID) and VID (Voltage ID). Unlike

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768-525: A reduced cache size use a separate naming scheme, which means that the releases are no longer in alphabetic order. Added steppings have been used in internal and engineering samples, but are unlisted in the tables. Many of the high-end Core 2 and Xeon processors use Multi-chip modules of two chips in order to get larger cache sizes or more than two cores. Early ES/QS steppings are: B0 (CPUID 6F4h), B1 (6F5h) and E0 (6F9h). Steppings B2/B3, E1, and G0 of model 15 (cpuid 06fx) processors are evolutionary steps of

832-462: A specified thread, independently from the other logical processor sharing the same physical core. Unlike a traditional dual-processor configuration that uses two separate physical processors, the logical processors in a hyper-threaded core share the execution resources. These resources include the execution engine, caches, and system bus interface; the sharing of resources allows two logical processors to work with each other more efficiently, and allows

896-414: A total of four logical processors). If the operating system's thread scheduler is unaware of hyper-threading, it will treat all four logical processors the same. If only two threads are eligible to run, it might choose to schedule those threads on the two logical processors that happen to belong to the same physical processor. That processor would be extremely busy, and would share execution resources, while

960-404: Is a form of simultaneous multithreading technology introduced by Intel, while the concept behind the technology has been patented by Sun Microsystems . Architecturally, a processor with Hyper-Threading Technology consists of two logical processors per core, each of which has its own processor architectural state. Each logical processor can be individually halted, interrupted or directed to execute

1024-569: Is a multi-core processor microarchitecture launched by Intel in mid-2006. It is a major evolution over the Yonah , the previous iteration of the P6 microarchitecture series which started in 1995 with Pentium Pro . It also replaced the NetBurst microarchitecture, which suffered from high power consumption and heat intensity due to an inefficient pipeline designed for high clock rate . In early 2004

1088-488: Is commonly called Penryn-3M and Wolfdale-3M and Yorkfield-6M, respectively. The single-core version of Penryn, listed as Penryn-L here, is not a separate model like Merom-L but a version of the Penryn-3M model with only one active core. The Xeon "Dunnington" processor (CPUID Family 6, model 29) is closely related to Wolfdale but comes with six cores and an on-chip L3 cache and is designed for servers with Socket 604, so it

1152-520: Is due to the replay system of the Pentium ;4 tying up valuable execution resources, equalizing the processor resources between the two programs, which adds a varying amount of execution time. The Pentium 4 "Prescott" and the Xeon "Nocona" processors received a replay queue that reduces execution time needed for the replay system and completely overcomes the performance penalty. According to

1216-407: Is marketed only as Xeon, not as Core 2. The Core microarchitecture uses several stepping levels (steppings), which unlike prior microarchitectures, represent incremental improvements, and different sets of features like cache size and low power modes. Most of these steppings are used across brands, typically by disabling some features and limiting clock frequencies on low-end chips. Steppings with

1280-421: Is physically present, the operating system addresses two virtual (logical) cores and shares the workload between them when possible. The main function of hyper-threading is to increase the number of independent instructions in the pipeline; it takes advantage of superscalar architecture, in which multiple instructions operate on separate data in parallel . With HTT, one physical core appears as two processors to

1344-423: Is that installing interleaved RAM will offer double the bandwidth. However, at most the increase in bandwidth by installing interleaved RAM is roughly 5–10%. The AGTL+ PSB used by all NetBurst processors and current and medium-term (pre- QuickPath ) Core 2 processors provide a 64-bit data path. Current chipsets provide for a couple of either DDR2 or DDR3 channels. On jobs requiring large amounts of memory access,

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1408-502: Is there a significant performance increase. While DDR2 memory models with tighter timing specifications do improve performance, the difference in real world games and applications is often negligible. Optimally, the memory bandwidth afforded should match the bandwidth of the FSB, that is to say that a CPU with a 533 MT/s rated bus speed should be paired with RAM matching the same rated speed, for example DDR2 533, or PC2-4200. A common myth

1472-418: Is to use performance tools to understand what areas contribute to performance gains and what areas contribute to performance degradation. As a result, performance improvements are very application-dependent; however, when running two programs that require full attention of the processor, it can actually seem like one or both of the programs slows down slightly when Hyper-Threading Technology is turned on. This

1536-491: Is transparent to operating systems and programs. The minimum that is required to take advantage of hyper-threading is symmetric multiprocessing (SMP) support in the operating system, since the logical processors appear no different to the operating system than physical processors. It is possible to optimize operating system behavior on multi-processor, hyper-threading capable systems. For example, consider an SMP system with two physical processors that are both hyper-threaded (for

1600-543: The CPU power dissipation tables. Like the last NetBurst CPUs, Core based processors feature multiple cores and hardware virtualization support (marketed as Intel VT-x ), and Intel 64 and SSSE3 . However, Core-based processors do not have the hyper-threading technology as in Pentium 4 processors. This is because the Core microarchitecture is based on the P6 microarchitecture used by Pentium Pro, II, III, and M. The L1 cache of

1664-510: The Core microarchitecture did not have hyper-threading because the Core microarchitecture was a descendant of the older P6 microarchitecture . The P6 microarchitecture was used in earlier iterations of Pentium processors, namely, the Pentium Pro , Pentium II and Pentium III (plus their Celeron & Xeon derivatives at the time). Windows 2000 SP3 and Windows XP SP1 have added support for hyper-threading. Intel released

1728-674: The Nehalem microarchitecture (Core i7) in November 2008, in which hyper-threading made a return. The first generation Nehalem processors contained four physical cores and effectively scaled to eight threads. Since then, both two- and six-core models have been released, scaling four and twelve threads respectively. Earlier Intel Atom cores were in-order processors, sometimes with hyper-threading ability, for low power mobile PCs and low-price desktop PCs. The Itanium  9300 launched with eight threads per processor (two threads per core) through enhanced hyper-threading technology. The next model,

1792-518: The Nehalem microarchitecture . While the Core microarchitecture is a major architectural revision, it is based in part on the Pentium M processor family designed by Intel Israel. The pipeline of Core/ Penryn is 14 stages long – less than half of Prescott 's. Penryn's successor Nehalem has a two cycles higher branch misprediction penalty than Core/Penryn. Core can ideally sustain up to 4 instructions per cycle (IPC) execution rate, compared to

1856-662: The 2007/2008 "Tick" was the shrink of the Core microarchitecture to 45 nanometers as CPUID model 23. In Core 2 processors, it is used with the code names Penryn (Socket P), Wolfdale (LGA 775) and Yorkfield (MCM, LGA 775), some of which are also sold as Celeron, Pentium and Xeon processors. In the Xeon brand, the Wolfdale-DP and Harpertown code names are used for LGA 771 based MCMs with two or four active Wolfdale cores. Architecturally, 45 nm Core 2 processors feature SSE4.1 and new divide/shuffle engine. The chips come in two sizes, with 6 MB and 3 MB L2 cache. The smaller version

1920-417: The 3 IPC capability of P6 , Pentium M and NetBurst microarchitectures. The new architecture is a dual core design with a shared L2 cache engineered for maximum performance per watt and improved scalability. One new technology included in the design is Macro-Ops Fusion , which combines two x86 instructions into a single micro-operation . For example, a common code sequence like a compare followed by

1984-619: The 3.0 GHz Woodcrest, and 40 or 35 watts for the low-voltage Woodcrest. In comparison, a 2.2 GHz AMD Opteron 875HE processor consumes 55 watts, while the energy efficient Socket AM2 line fits in the 35 watt thermal envelope (specified a different way so not directly comparable). Merom, the mobile variant, is listed at 35 watts TDP for standard versions and 5 watts TDP for ultra low voltage (ULV) versions. Previously, Intel announced that it would now focus on power efficiency, rather than raw performance. However, at Intel Developer Forum (IDF) in spring 2006, Intel advertised both. Some of

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2048-545: The Core microarchitecture at 64 KB L1 cache/core (32 KB L1 Data + 32 KB L1 Instruction) is as large as in Pentium M, up from 32 KB on Pentium II / III (16 KB L1 Data + 16 KB L1 Instruction). The consumer version also lacks an L3 cache as in the Gallatin core of the Pentium 4 Extreme Edition, though it is exclusively present in high-end versions of Core-based Xeons. Both an L3 cache and hyper-threading were reintroduced again to consumer line in

2112-477: The Foster MP-based Xeon . It was also included on the 3.06 GHz Northwood-based Pentium 4 in the same year, and then remained as a feature in every Pentium 4 HT, Pentium 4 Extreme Edition and Pentium Extreme Edition processor since. The Intel Core & Core 2 processor lines (2006) that succeeded the Pentium 4 model line didn't utilize hyper-threading. The processors based on

2176-485: The Itanium 9500 (Poulson), features a 12-wide issue architecture, with eight CPU cores with support for eight more virtual cores via hyper-threading. The Intel Xeon 5500 server chips also utilize two-way hyper-threading. According to Intel, the first hyper-threading implementation used only 5% more die area than the comparable non-hyperthreaded processor, but the performance was 15–30% better. Intel claims up to

2240-517: The Mobile Intel 965 Express ( Santa Rosa ) platform with Socket P , while the earlier B2 and L2 steppings only appear for the Socket M based Mobile Intel 945 Express ( Napa refresh ) platform. The model 22 stepping A1 (cpuid 10661h) marks a significant design change, with just a single core and 1 MB L2 cache further reducing the power consumption and manufacturing cost for the low-end. Like

2304-630: The Penryn technology, and the QX9775 is only compatible with the Intel D5400XS motherboard. The Wolfdale-3M model E7200 also has limited compatibility (at least the Xpress 200 chipset is incompatible ). Although a motherboard may have the required chipset to support Conroe, some motherboards based on the above-mentioned chipsets do not support Conroe. This is because all Conroe-based processors require

2368-515: The Xeon brand. The Conroe-L and Merom-L processors are based around the same core as Conroe and Merom, but only contain a single core and 1 MB of L2 cache, significantly reducing production cost and power consumption of the processor at the expense of performance compared to the dual-core version. It is used only in ultra-low voltage Core 2 Solo U2xxx and in Celeron processors and is identified as CPUID family 6 model 22. In Intel's Tick-Tock cycle,

2432-425: The additional hardware resource utilization provided by hyper-threading. A similar performance analysis is available for the effects of hyper-threading when used to handle tasks related to managing network traffic, such as for processing interrupt requests generated by network interface controllers (NICs). Another paper claims no performance improvements when hyper-threading is used for interrupt handling. When

2496-483: The chip to produce less heat, and minimize power use. For most Woodcrest CPUs, the front-side bus (FSB) runs at 1333 MT/s ; however, this is scaled down to 1066 MT/s for lower end 1.60 and 1.86 GHz variants. The Merom mobile variant was initially targeted to run at an FSB of 667 MT/s while the second wave of Meroms, supporting 800 MT/s FSB, were released as part of the Santa Rosa platform with

2560-415: The choice of a short and efficient pipeline, delivering superior performance despite not reaching the high clocks of NetBurst. The first processors that used this architecture were code-named ' Merom ', ' Conroe ', and ' Woodcrest '; Merom is for mobile computing, Conroe is for desktop systems, and Woodcrest is for servers and workstations. While architecturally identical, the three processor lines differ in

2624-535: The coming months" with information on recommended methods of managing the translation lookaside buffer (TLB) for Core 2 to avoid issues, and admits that, "in rare instances, improper TLB invalidation may result in unpredictable system behavior, such as hangs or incorrect data." Among the issues stated: Intel errata Ax39, Ax43, Ax65, Ax79, Ax90, Ax99 are said to be particularly serious. 39, 43, 79, which can cause unpredictable behavior or system hang, have been fixed in recent steppings . Among those who have stated

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2688-432: The earlier steppings, A1 is not used with the Mobile Intel 965 Express platform. Steppings G0, M0 and A1 mostly replaced all older steppings in 2008. In 2009, a new stepping G2 was introduced to replace the original stepping B2. In the model 23 (cpuid 01067xh), Intel started marketing stepping with full (6 MB) and reduced (3 MB) L2 cache at the same time, and giving them identical cpuid values. All steppings have

2752-506: The errata to be particularly serious are OpenBSD 's Theo de Raadt and DragonFly BSD 's Matthew Dillon . Taking a contrasting view was Linus Torvalds , calling the TLB issue "totally insignificant", adding, "The biggest problem is that Intel should just have documented the TLB behavior better." Microsoft has issued update KB936357 to address the errata by microcode update, with no performance penalty. BIOS updates are also available to fix

2816-497: The first HT processors were released, many operating systems were not optimized for hyper-threading technology (e.g. Windows 2000 and Linux older than 2.4). In 2006, hyper-threading was criticised for energy inefficiency. For example, ARM (a specialized, low-power, CPU design company), stated that simultaneous multithreading can use up to 46% more power than ordinary dual-core designs. Furthermore, they claimed that SMT increases cache thrashing by 42%, whereas dual core results in

2880-736: The issue. Hyper-threading Hyper-threading (officially called Hyper-Threading Technology or HT Technology and abbreviated as HTT or HT ) is Intel 's proprietary simultaneous multithreading (SMT) implementation used to improve parallelization of computations (doing multiple tasks at once) performed on x86 microprocessors. It was introduced on Xeon server processors in February 2002 and on Pentium 4 desktop processors in November 2002. Since then, Intel has included this technology in Itanium , Atom , and Core 'i' Series CPUs, among others. For each processor core that

2944-463: The lower available memory bandwidth. The Core 2 memory management unit (MMU) in X6800, E6000 and E4000 processors does not operate to prior specifications implemented in prior generations of x86 hardware. This may cause problems, many of them serious security and stability issues, with extant operating system software. Intel's documentation states that their programming manuals will be updated "in

3008-458: The mobile and desktop processors come in two variants that differ in the size of the L2 cache, but the specific amount of L2 cache in a product can also be reduced by disabling parts at production time. Tigerton dual-cores and all quad-core processors except - are multi-chip modules combining two dies. For the 65 nm processors, the same product code can be shared by processors with different dies, but

3072-571: The new SSE4.1 instructions. Stepping C1/M1 was a bug fix version of C0/M0 specifically for quad core processors and only used in those. Stepping E0/R0 adds two new instructions (XSAVE/XRSTOR) and replaces all earlier steppings. In mobile processors, stepping C0/M0 is only used in the Intel Mobile 965 Express ( Santa Rosa refresh ) platform, whereas stepping E0/R0 supports the later Intel Mobile 4 Express ( Montevina ) platform. Model 30 stepping A1 (cpuid 106d1h) adds an L3 cache and six instead of

3136-491: The new version of NetBurst (Prescott) needed very high power to reach the clocks it needed for competitive performance, making it unsuitable for the shift to dual/multi-core CPUs. On May 7, 2004 Intel confirmed the cancellation of the next NetBurst, Tejas and Jayhawk . Intel had been developing Merom, the 64-bit evolution of the Pentium M , since 2001, and decided to expand it to all market segments, replacing NetBurst in desktop computers and servers. It inherited from Pentium M

3200-415: The operating system to schedule two threads or processes simultaneously and appropriately. When execution resources in a hyper-threaded processor are not in use by the current task, and especially when the processor is stalled, those execution resources can be used to execute another scheduled task. (The processor may stall due to a cache miss , branch misprediction , or data dependency .) This technology

3264-478: The operating system, allowing concurrent scheduling of two processes per core. In addition, two or more processes can use the same resources: If resources for one process are not available, then another process can continue if its resources are available. In addition to requiring simultaneous multithreading support in the operating system, hyper-threading can be properly utilized only with an operating system specifically optimized for it. Hyper-Threading Technology

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3328-428: The other processor would remain idle, leading to poorer performance than if the threads were scheduled on different physical processors. This problem can be avoided by improving the scheduler to treat logical processors differently from physical processors, which is, in a sense, a limited form of the scheduler changes required for NUMA systems. The first published paper describing what is now known as hyper-threading in

3392-416: The performance history of hyper-threading was a mixed one in the beginning. As one commentary on high-performance computing from November 2002 notes: Hyper-Threading can improve the performance of some MPI applications, but not all. Depending on the cluster configuration and, most importantly, the nature of the application running on the cluster, performance gains can vary or even be negative. The next step

3456-420: The preceding NetBurst microarchitecture of the Pentium 4 and D -branded CPUs. The Core microarchitecture provides more efficient decoding stages, execution units, caches , and buses , reducing the power consumption of Core 2-branded CPUs while increasing their processing capacity. Intel's CPUs have varied widely in power consumption according to clock rate, architecture, and semiconductor process, shown in

3520-462: The prior Pentium 4 and Pentium D design, the Core 2 technology sees a greater benefit from memory running synchronously with the front-side bus (FSB). This means that for the Conroe CPUs with FSB of 1066 MT/s, the ideal memory performance for DDR2 is PC2-8500 . In a few configurations, using PC2-5300 instead of PC2-4200 can actually decrease performance. Only when going to PC2-6400

3584-417: The processor efficiently. Hyper-threading works by duplicating certain sections of the processor—those that store the architectural state —but not duplicating the main execution resources . This allows a hyper-threading processor to appear as the usual "physical" processor plus an extra " logical " processor to the host operating system (HTT-unaware operating systems see two "physical" processors), allowing

3648-475: The promised numbers were: The processors of the Core microarchitecture can be categorized by number of cores, cache size, and socket; each combination of these has a unique code name and product code that is used across several brands. For instance, code name "Allendale" with product code 80557 has two cores, 2 MB L2 cache and uses the desktop socket 775, but has been marketed as Celeron, Pentium, Core 2, and Xeon, each with different sets of features enabled. Most of

3712-582: The quad-core Core 2 processors can benefit significantly from using PC2-8500 memory, which runs at the same speed as the CPU's FSB; this is not an officially supported configuration, but several motherboards support it. The Core 2 processor does not require the use of DDR2. While the Intel 975X and P965 chipsets require this memory, some motherboards and chipsets support both Core 2 processors and DDR memory. When using DDR memory, performance may be reduced because of

3776-434: The socket used, bus speed, and power consumption. The first Core-based desktop and mobile processors were branded Core 2 , later expanding to the lower-end Pentium Dual-Core , Pentium and Celeron brands; while server and workstation Core-based processors were branded Xeon . The Core microarchitecture returned to lower clock rates and improved the use of both available clock cycles and power when compared with

3840-914: The specific information about which one is used can be derived from the stepping. The original Core 2 processors are based on the same dies that can be identified as CPUID Family 6 Model 15. Depending on their configuration and packaging, their code names are Conroe ( LGA 775 , 4 MB L2 cache), Allendale (LGA 775, 2 MB L2 cache), Merom ( Socket M , 4 MB L2 cache) and Kentsfield ( multi-chip module , LGA 775, 2x4MB L2 cache). Merom and Allendale processors with limited features are in Pentium Dual Core and Celeron processors, while Conroe, Allendale and Kentsfield also are sold as Xeon processors. Additional code names for processors based on this model are Woodcrest (LGA 771, 4 MB L2 cache), Clovertown (MCM, LGA 771, 2×4MB L2 cache) and Tigerton (MCM, Socket 604 , 2×4MB L2 cache), all of which are marketed only under

3904-652: The standard Merom/Conroe die with 4 MB L2 cache, with the short-lived E1 stepping only being used in mobile processors. Stepping L2 and M0 are the Allendale chips with just 2 MB L2 cache, reducing production cost and power consumption for low-end processors. The G0 and M0 steppings improve idle power consumption in C1E state and add the C2E state in desktop processors. In mobile processors, all of which support C1 through C4 idle states, steppings E1, G0, and M0 add support for

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3968-541: The table below, satsw (X) (read as 'saturate to signed word') takes a signed integer X, and converts it to −32768 if it is less than −32768, to +32767 if it is greater than 32767, and leaves it unchanged otherwise. As normal for the Intel architecture, bytes are 8 bits, words 16 bits, and dwords 32 bits; 'register' refers to an MMX or XMM vector register. Intel Core (microarchitecture) The Intel Core microarchitecture (provisionally referred to as Next Generation Micro-architecture , and developed as Merom )

4032-619: The usual two cores, which leads to an unusually large die size of 503 mm . As of February 2008, it has only found its way into the very high-end Xeon 7400 series ( Dunnington ). Conroe, Conroe XE and Allendale all use Socket LGA 775 ; however, not every motherboard is compatible with these processors. Supporting chipsets are: The Yorkfield XE model QX9770 (45 nm with 1600 MT/s FSB) has limited chipset compatibility - with only X38, P35 (with overclocking ) and some high-performance X48 and P45 motherboards being compatible. BIOS updates were gradually being released to provide support for

4096-651: Was revealed that Intel's Skylake and Kaby Lake processors had a bug in their implementation of hyper-threading that could cause data loss. Microcode updates were later released to address the issue. In 2019, with Coffee Lake , Intel temporarily moved away from including hyper-threading in mainstream Core i7 desktop processors except for highest-end Core i9 parts or Pentium Gold CPUs. It also began to recommend disabling hyper-threading, as new CPU vulnerability attacks were revealed which could be mitigated by disabling HT. In May 2005, Colin Percival demonstrated that

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