Intel Core (microarchitecture)

Intel Core
General information
Launched	July 27, 2006
Performance
Max. CPU clock rate	1.06 GHz to 3.33 GHz
FSB speeds	533 MT/s to 1600 MT/s
Cache
L1 cache	64 KB per core
L2 cache	1 MB to 8 MB unified
L3 cache	8 MB to 16 MB shared (Xeon)
Architecture and classification
Min. feature size	65 nm to 45 nm
Architecture	Intel Core x86
Instructions	x86, x86-64
Extensions	MMX, SSE, SSE2, SSE3, SSSE3, SSE4 (45nm Core 2 only), VT-x (some);
Physical specifications
Transistors	105M to 582M (65 nm);
Cores	1–4 (2-6 Xeon);
Socket(s)	Socket M (µPGA 478); Socket P (µPGA 478); Socket T (LGA 775); FCBGA (µBGA 479); FCBGA (µBGA 965);
Products, models, variants
Model(s)	P6 family (Celeron, Pentium, Pentium Dual-Core, Core 2 range, Xeon);
History
Predecessor	NetBurst; Enhanced Pentium M (P6)
Successor	Penryn (tick); Nehalem (tock)

The Intel Core microarchitecture (formerly named Next-Generation Micro-Architecture) is a multi-core processor microarchitecture unveiled by Intel in Q1 2006. It is based on the Yonah processor design and can be considered an iteration of the P6 microarchitecture introduced in 1995 with Pentium Pro. High power consumption and heat intensity, the resulting inability to effectively increase clock rate, and other shortcomings such as an inefficient pipeline were the primary reasons why Intel abandoned the NetBurst microarchitecture and switched to a different architectural design, delivering high efficiency through a small pipeline rather than high clock rates. The Core microarchitecture initially did not reach the clock rates of the NetBurst microarchitecture, even after moving to 45 nm lithography. However after many generations of successor microarchitectures which used Core as their basis (such as Nehalem, Sandy Bridge and more), Intel managed to eventually surpass the clock rates of Netburst with the Devil's Canyon (Improved version of Haswell) microarchitecture reaching a base frequency of 4 GHz and a maximum tested frequency of 4.4 GHz using 22 nm lithography.

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 the socket used, bus speed, and power consumption. The initial mainstream Core-based processors were branded Pentium Dual-Core or Pentium and low end branded Celeron; server and workstation Core-based processors were branded Xeon, while Intel's first 64-bit desktop and mobile Core-based processors were branded Core 2.

Features

The Core microarchitecture returned to lower clock rates and improved the use of both available clock cycles and power when compared with the preceding NetBurst microarchitecture of the Pentium 4 and D-branded CPUs.[1] 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 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 size was enlarged in the Core microarchitecture, from 32 KB on Pentium II / III (16 KB L1 Data + 16 KB L1 Instruction) to 64 KB L1 cache/core (32 KB L1 Data + 32 KB L1 Instruction) on Pentium M and Core/Core 2. 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 the Nehalem microarchitecture.

Roadmap

Technology

Intel Core 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.[2] The Penryn pipeline is 12–14 stages long[3] – less than half of Prescott's, a signature feature of wide order execution cores. Penryn's successor, Nehalem borrowed more heavily from the Pentium 4 and has 20-24 pipeline stages.[3] Core's execution unit is 4 issues wide, compared to the 3-issue cores of P6, Pentium M, and 2-issue cores of NetBurst microarchitectures. The new architecture is a dual core design with linked L1 cache and 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 a conditional jump would become a single micro-op. However, this technology does not work in 64-bit mode.

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 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.[4][5] 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 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 new 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 the 3.0 GHz Woodcrest, and 40 watts for the low-voltage Woodcrest. In comparison, an 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 the promised numbers were:

20% more performance for Merom at the same power level; compared to Core Duo
40% more performance for Conroe at 40% less power; compared to Pentium D
80% more performance for Woodcrest at 35% less power; compared to the original dual-core Xeon

Processor cores

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 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. Wolfdale-DP and all quad-core processors except Dunnington QC 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 the specific information about which one is used can be derived from the stepping.

	fab	cores	Mobile		Desktop, UP Server		CL Server	DP Server	MP Server
Single-Core 65 nm	65 nm	1	Merom-L 80537		Conroe-L 80557
Single-Core 45 nm	45 nm	1		Penryn-L 80585				Wolfdale-CL 80588
Dual-Core 65 nm	65 nm	2	Merom-2M 80537	Merom 80537	Allendale 80557	Conroe 80557	Conroe-CL 80556	Woodcrest 80556	Tigerton-DC 80564
Dual-Core 45 nm	45 nm	2	Penryn-3M 80577	Penryn 80576	Wolfdale-3M 80571	Wolfdale 80570	Wolfdale-CL 80588	Wolfdale-DP 80573
Quad-Core 65 nm	65 nm	4				Kentsfield 80562		Clovertown 80563	Tigerton 80565
Quad-Core 45 nm	45 nm	4		Penryn-QC 80581	Yorkfield-6M 80580	Yorkfield 80569	Yorkfield-CL 80584	Harpertown 80574	Dunnington QC 80583
Six-Core 45 nm	45 nm	6							Dunnington 80582

Conroe/Merom (65 nm)

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 the Xeon brand.

Processor	Brand name	Model (list)	Cores	L2 Cache	Socket	TDP
Merom-2M	Mobile Core 2 Duo	U7xxx	2	2 MiB	BGA479	10 W
Merom		L7xxx		4 MiB	BGA479	17 W
Merom Merom-2M		T5xxx T7xxx		2–4 MiB	Socket M Socket P BGA479	35 W
Merom	Mobile Core 2 Extreme	X7xxx	2	4 MiB	Socket P	44 W
Merom	Celeron M	5x0	1	1 MiB	Socket M Socket P	30 W
Merom-2M	Celeron M	5x5	1	1 MiB	Socket P	31 W
Merom-2M	Celeron Dual-Core	T1xxx	2	512–1024 KiB	Socket P	35 W
Merom-2M	Pentium Dual-Core	T2xxx T3xxx	2	1 MiB	Socket P	35 W
Allendale	Xeon	3xxx	2	2 MB	LGA 775	65 W
Conroe	Xeon	3xxx	2	2–4 MB	LGA 775	65 W
Conroe and Allendale	Core 2 Duo	E4xxx	2	2 MB	LGA 775	65 W
Conroe and Allendale		E6xx0		2–4 MB	LGA 775
Conroe-CL		E6xx5		2–4 MB	LGA 771
Conroe-XE	Core 2 Extreme	X6xxx	2	4 MB	LGA 775	75 W
Allendale	Pentium Dual-Core	E2xxx	2	1 MB	LGA 775	65 W
Allendale	Celeron	E1xxx	2	512 KB	LGA 775	65 W
Kentsfield	Xeon	32xx	4	2×4 MiB	LGA 775	95–105 W
Kentsfield	Core 2 Quad	Q6xxx	4	2×4 MiB	LGA 775	95–105 W
Kentsfield XE	Core 2 Extreme	QX6xxx	4	2×4 MiB	LGA 775	130 W
Woodcrest	Xeon	51xx	2	4 MB	LGA 771	65–80 W
Clovertown		L53xx	4	2×4 MB	LGA 771	40–50 W
		E53xx				80 W
		X53xx				120–150 W
Tigerton-DC		E72xx	2	2×4 MB	Socket 604	80 W
Tigerton		L73xx	4	2×4 MB		50 W
		E73xx		2×2–2×4 MB		80 W
		X73xx		2×4 MB		130 W

Conroe-L/Merom-L

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.

Processor	Brand name	Model (list)	Cores	L2 Cache	Socket	TDP
Merom-L	Mobile Core 2 Solo	U2xxx	1	2 MiB	BGA479	5.5 W
Merom-L	Celeron M	5x0	1	512 KiB	Socket M Socket P	27 W
Merom-L	Celeron M	5x3	1	512–1024 KiB	BGA479	5.5–10 W
Conroe-L	Celeron M	4x0	1	512 KiB	LGA 775	35 W
Conroe-CL	Celeron M	4x5	1	512 KiB	LGA 771	65 W

Penryn/Wolfdale (45 nm)

In Intel's Tick-Tock cycle, 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, 45nm Core 2 processors feature SSE4.1 and new divide/shuffle engine.[6]

The chips come in two sizes, with 6 MB and 3 MB L2 cache. The smaller version 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.

Processor	Brand name	Model (list)	Cores	L2 Cache	Socket	TDP
Penryn-L	Core 2 Solo	SU3xxx	1	3 MiB	BGA956	5.5 W
Penryn-3M	Core 2 Duo	SU7xxx	2	3 MB	BGA956	10 W
Penryn-3M		SU9xxx		3 MB		10 W
Penryn		SL9xxx		6 MiB		17 W
Penryn		SP9xxx		6 MiB		25/28 W
Penryn-3M		P7xxx		3 MiB	Socket P FCBGA6	25 W
Penryn-3M		P8xxx		3 MiB
Penryn		P9xxx		6 MiB
Penryn-3M		T6xxx		2 MiB		35 W
Penryn-3M		T8xxx		3 MiB
Penryn		T9xxx		6 MiB
Penryn		E8x35		6 MiB	Socket P	35-55 W
Penryn-QC	Core 2 Quad	Q9xxx	4	2x3-2x6 MiB	Socket P	45 W
Penryn XE	Core 2 Extreme	X9xxx	2	6 MiB	Socket P	44 W
Penryn-QC	Core 2 Extreme	QX9xxx	4	2x6 MiB	Socket P	45 W
Penryn-3M	Celeron	T3xxx	2	1 MiB	Socket P	35 W
Penryn-3M		SU2xxx	2	1 MiB	µFC-BGA 956	10 W
Penryn-L		9x0	1	1 MiB	Socket P	35 W
Penryn-L		7x3	1	1 MiB	µFC-BGA 956	10 W
Penryn-3M	Pentium	T4xxx	2	1 MiB	Socket P	35 W
Penryn-3M		SU4xxx	2	2 MiB	µFC-BGA 956	10 W
Penryn-L		SU2xxx	1	2 MiB	µFC-BGA 956	5.5 W
Wolfdale-3M
	Celeron	E3xxx	2	1 MB	LGA 775	65 W
	Pentium	E2210		1 MB
		E5xxx		2 MB
		E6xxx		2 MB
	Core 2 Duo	E7xxx		3 MB
Wolfdale	Core 2 Duo	E8xxx		6 MB
Wolfdale	Xeon	31x0				45-65 W
Wolfdale-CL		30x4	1		LGA 771	30 W
Wolfdale-CL		31x3	2		LGA 771	65 W
Yorkfield	Xeon	X33x0	4	2×3–2×6 MB	LGA 775	65–95 W
Yorkfield-CL	Xeon	X33x3		2×3–2×6 MB	LGA 771	80 W
Yorkfield-6M	Core 2 Quad	Q8xxx		2×2 MB	LGA 775	65–95 W
Yorkfield-6M		Q9x0x		2×3 MB
Yorkfield		Q9x5x		2×6 MB
Yorkfield XE	Core 2 Extreme	QX9xxx		2×6 MB		130–136 W
Yorkfield XE	Core 2 Extreme	QX9xx5		2×6 MB	LGA 771	150 W
Wolfdale-DP	Xeon	E52xx	2	6 MB	LGA 771	65 W
		L52xx				20-55 W
		X52xx				80 W
Harpertown		E54xx	4	2×6 MB	LGA 771	80 W
		L54xx				40-50 W
		X54xx				120-150 W

Dunnington

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 is marketed only as Xeon, not as Core 2.

Processor	Brand name	Model (list)	Cores	L3 cache	Socket	TDP
Dunnington	Xeon	E74xx	4-6	8-16 MB	Socket 604	90 W
		L74xx	4-6	12 MB		50-65 W
		X7460	6	16 MB		130 W

Steppings

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 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 or three chips in order to get larger cache sizes or more than two cores.

Steppings using 65 nm process

Stepping	Released	Area	CPUID	L2 cache	Max. clock	Celeron	Pentium	Core 2	Celeron	Pentium	Core 2	Xeon	Core 2	Xeon	Xeon
						Mobile (Merom)			Desktop (Conroe)				Desktop (Kentsfield)		Server (Woodcrest, Clovertown, Tigerton)
B2	Jul 2006	143 mm²	06F6	4 MiB	2.93 GHz	M5xx		T5000 T7000 L7000			E6000 X6000	3000			5100
B3	Nov 2006	143 mm²	06F7	4 MiB	3.00 GHz								Q6000 QX6000	3200	5300
L2	Jan 2007	111 mm²	06F2	2 MiB	2.13 GHz			T5000 U7000		E2000	E4000 E6000	3000
E1	May 2007	143 mm²	06FA	4 MiB	2.80 GHz	M5xx		T7000 L7000 X7000
G0	Apr 2007	143 mm²	06FB	4 MiB	3.00 GHz	M5xx		T7000 L7000 X7000		E2000	E4000 E6000	3000	Q6000 QX6000	3200	5100 5300 7200 7300
G2	Mar 2009	143 mm²	06FB	4 MiB	2.16 GHz	M5xx		T5000 T7000 L7000
M0	Jul 2007	111 mm²	06FD	2 MiB	2.40 GHz	5xx T1000	T2000 T3000	T5000 T7000 U7000	E1000	E2000	E4000
A1	Jun 2007	81 mm²	10661	1 MiB	2.20 GHz	M5xx		U2000	220 4x0

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 the standard Merom/Conroe die with 4 MiB 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 MiB 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 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 MiB L2 cache further reducing the power consumption and manufacturing cost for the low-end. Like 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.[7]

Steppings using 45 nm process

Stepping	Released	Area	CPUID	L2 cache	Max. clock	Celeron	Pentium	Core 2	Celeron	Pentium	Core 2	Xeon	Core 2	Xeon	Xeon
						Mobile (Penryn)			Desktop (Wolfdale)				Desktop (Yorkfield)		Server (Wolfdale-DP, Harpertown, Dunnington)
C0	Nov 2007	107 mm²	10676	6 MiB	3.00 GHz			E8000 P7000 T8000 T9000 P9000 SP9000 SL9000 X9000			E8000	3100	QX9000		5200 5400
M0	Mar 2008	82 mm²	10676	3 MiB	2.40 GHz	7xx		SU3000 P7000 P8000 T8000 SU9000		E5000 E2000	E7000
C1	Mar 2008	107 mm²	10677	6 MiB	3.20 GHz								Q9000 QX9000	3300
M1	Mar 2008	82 mm²	10677	3 MiB	2.50 GHz								Q8000 Q9000	3300
E0	Aug 2008	107 mm²	1067A	6 MiB	3.33 GHz			T9000 P9000 SP9000 SL9000 Q9000 QX9000			E8000	3100	Q9000 Q9000S QX9000	3300	5200 5400
R0	Aug 2008	82 mm²	1067A	3 MiB	2.93 GHz	7xx 900 SU2000 T3000	T4000 SU2000 SU4000	SU3000 T6000 SU7000 P8000 SU9000	E3000	E5000 E6000	E7000		Q8000 Q8000S Q9000 Q9000S	3300
A1	Sep 2008	503 mm²	106D1	3 MiB	2.67 GHz										7400

In the model 23 (cpuid 01067xh), Intel started marketing stepping with full (6 MiB) and reduced (3 MiB) L2 cache at the same time, and giving them identical cpuid values. All steppings have 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 the usual two cores, which leads to an unusually large die size of 503 mm².[8] As of February 2008, it has only found its way into the very high-end Xeon 7400 series (Dunnington).

System requirements

Motherboard compatibility

Conroe, Conroe XE and Allendale all use Socket LGA 775; however, not every motherboard is compatible with these processors.

Supporting chipsets are:

Intel: 865G/PE/P, 945G/GZ/GC/P/PL, 965G/P, 975X, P/G/Q965, Q963, 946GZ/PL, P3x, G3x, Q3x, X38, X48, P4x, 5400 Express See also: List of Intel chipsets
NVIDIA: nForce4 Ultra/SLI X16 for Intel, nForce 570/590 SLI for Intel, nForce 650i Ultra/650i SLI/680i LT SLI/680i SLI and nForce 750i SLI/780i SLI/790i SLI/790i Ultra SLI.
VIA: P4M800, P4M800PRO, P4M890, P4M900, PT880 Pro/Ultra, PT890. See also: List of VIA chipsets
SiS: 662, 671, 671fx, 672, 672fx
ATI: Radeon Xpress 200 and CrossFire Xpress 3200 for Intel

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 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 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).

Synchronous memory modules

Unlike 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 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.[9]

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 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.

Matched processor and RAM ratings
Processor model	Front-side bus	Matched memory and maximum bandwidth single channel, dual channel
Processor model	Front-side bus	DDR	DDR2	DDR3
Mobile: T5200, T5300, U2n00, U7n00	533 MT/s	PC-3200 (DDR-400) 3.2 GB/s	PC2-4200 (DDR2-533) 4.264 GB/s PC2-8500 (DDR2-1066) 8.532 GB/s	PC3-8500 (DDR3-1066) 8.530 GB/s
Desktop: E6n00, E6n20, X6n00, E7n00, Q6n00 and QX6n00 Mobile: T9400, T9550, T9600, P7350, P7450, P8400, P8600, P8700, P9500, P9600, SP9300, SP9400, X9100	1066 MT/s	PC-3200 (DDR-400) 3.2 GB/s		PC3-8500 (DDR3-1066) 8.530 GB/s
Mobile: T5n00, T5n50, T7n00 (Socket M), L7200, L7400	667 MT/s	PC-3200 (DDR-400) 3.2 GB/s	PC2-5300 (DDR2-667) 5.336 GB/s	PC3-10600 (DDR3-1333) 10.670 GB/s
Desktop: E6n40, E6n50, E8nn0, Q9nn0, QX6n50, QX9650	1333 MT/s	PC-3200 (DDR-400) 3.2 GB/s	PC2-5300 (DDR2-667) 5.336 GB/s	PC3-10600 (DDR3-1333) 10.670 GB/s
Mobile: T5n70, T6400, T7n00 (Socket P), L7300, L7500, X7n00, T8n00, T9300, T9500, X9000 Desktop: E4n00, Pentium E2nn0, Pentium E5nn0, Celeron 4n0, E3n00	800 MT/s	PC-3200 (DDR-400) 3.2 GB/s PC-3200 (DDR-400) 3.2 GB/s	PC2-6400 (DDR2-800) 6.400 GB/s PC2-8500 (DDR2-1066) 8.532 GB/s	PC3-6400 (DDR3-800) 6.400 GB/s PC3-12800 (DDR3-1600) 12.800 GB/s
Desktop: QX9770, QX9775	1600 MT/s	PC-3200 (DDR-400) 3.2 GB/s PC-3200 (DDR-400) 3.2 GB/s

On jobs requiring large amounts of memory access, the quad-core Core 2 processors can benefit significantly[10] 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 the lower available memory bandwidth.

Chip errata

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 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."[11]

Among the issues stated:

Non-execute bit is shared across the cores.
Floating point instruction non-coherencies.
Allowed memory corruptions outside of the range of permitted writing for a process by running common instruction sequences.

Intel errata Ax39, Ax43, Ax65, Ax79, Ax90, Ax99 are said to be particularly serious.[12] 39, 43, 79, which can cause unpredictable behavior or system hang, have been fixed in recent steppings.

Among those who have stated the errata to be particularly serious are OpenBSD's Theo de Raadt[13] and DragonFly BSD's Matthew Dillon.[14] 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."[15]

Microsoft has issued update KB936357 to address the errata by microcode update,[16] with no performance penalty. BIOS updates are also available to fix the issue.

References

"Penryn Arrives: Core 2 Extreme QX9650 Review". ExtremeTech. Archived from the original on October 31, 2007. Retrieved October 30, 2006.
King, Ian (April 9, 2007). "How Israel saved Intel". The Seattle Times. Retrieved April 15, 2012.
Swinburne, Richard (November 3, 2008). "Intel Core i7 – Nehalem Architecture Dive: 5 – Architecture Enhancements". Retrieved August 21, 2011.
"Intel Xeon Processor 5110". Intel. Retrieved April 15, 2012.
"Intel Xeon Processor 5120". Intel. Retrieved April 15, 2012.
http://www.anandtech.com/show/2362
"Product Change Notice" (PDF). Archived from the original (PDF) on December 22, 2010. Retrieved June 17, 2012.
"ARK entry for Intel Xeon Processor X7460". Intel. Retrieved July 14, 2009.
piotke (August 1, 2006). "Intel Core 2: Is high speed memory worth its price?". Madshrimps. Retrieved August 1, 2006.
Jacob (May 19, 2007). "Benchmarks of four Prime95 processes on a quad-core". Mersenne Forum. Retrieved May 22, 2007.
"Dual-Core Intel Xeon Processor 7200 Series and Quad-Core Intel Xeon Processor 7300 Series" (PDF). p. 46. Retrieved January 23, 2010.
"Intel Core 2 Duo Processor for Intel Centrino Duo Processor Technology Specification Update" (PDF). pp. 18–21.
marc.info
"Matthew Dillon on Intel Core Bugs". OpenBSD journal. June 30, 2007. Retrieved April 15, 2012.
Torvalds, Linus (June 27, 2007). "Core 2 Errata -- problematic or overblown?". Real World Technologies. Retrieved April 15, 2012.
"A microcode reliability update is available that improves the reliability of systems that use Intel processors". Microsoft. October 8, 2011. Retrieved April 15, 2012.

External links

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[1] "Penryn Arrives: Core 2 Extreme QX9650 Review". ExtremeTech. Archived from the original on October 31, 2007. Retrieved October 30, 2006.

[2] King, Ian (April 9, 2007). "How Israel saved Intel". The Seattle Times. Retrieved April 15, 2012.

[bittech08-3] Swinburne, Richard (November 3, 2008). "Intel Core i7 – Nehalem Architecture Dive: 5 – Architecture Enhancements". Retrieved August 21, 2011.

[4] "Intel Xeon Processor 5110". Intel. Retrieved April 15, 2012.

[5] "Intel Xeon Processor 5120". Intel. Retrieved April 15, 2012.

[6] ttp://www.anandtech.com/show/2362

[7] "Product Change Notice" (PDF). Archived from the original (PDF) on December 22, 2010. Retrieved June 17, 2012.

[8] "ARK entry for Intel Xeon Processor X7460". Intel. Retrieved July 14, 2009.

[9] tke (August 1, 2006). "Intel Core 2: Is high speed memory worth its price?". Madshrimps. Retrieved August 1, 2006.

[10] Jacob (May 19, 2007). "Benchmarks of four Prime95 processes on a quad-core". Mersenne Forum. Retrieved May 22, 2007.

[11] "Dual-Core Intel Xeon Processor 7200 Series and Quad-Core Intel Xeon Processor 7300 Series" (PDF). p. 46. Retrieved January 23, 2010.

[12] "Intel Core 2 Duo Processor for Intel Centrino Duo Processor Technology Specification Update" (PDF). pp. 18–21.

[13] rc.info

[14] "Matthew Dillon on Intel Core Bugs". OpenBSD journal. June 30, 2007. Retrieved April 15, 2012.

[15] Torvalds, Linus (June 27, 2007). "Core 2 Errata -- problematic or overblown?". Real World Technologies. Retrieved April 15, 2012.

[16] "A microcode reliability update is available that improves the reliability of systems that use Intel processors". Microsoft. October 8, 2011. Retrieved April 15, 2012.