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Central processing units are the brains behind any computer system.These series of pages provide specific information about the technicialities behind various Intel and AMD based processors.
On This Page:
smallbluedisk.gif 486.
smallbluedisk.gif Pentium and Pentium Pro
smallbluedisk.gif Socket 478
smallbluedisk.gif Socket LGA775
smallbluedisk.gif Socket LGA1156
smallbluedisk.gif Socket LGA1366
smallbluedisk.gif Socket LGA1155
smallbluedisk.gif Socket 939 and 940
smallbluedisk.gif Socket AM2/AM2+/AM3/AM3+
smallbluedisk.gif Socket F (1207FX)
smallbluedisk.gif
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Complete guide to Central Processing Units
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Processor Socket and Slot Types

Intel and AMD have created a set of socket and slot designs for their processors. Each socket or slot is designed to support a different range of original and upgrade processors. Table 3.10 shows the designations for the various standard processor sockets/slots and lists the chips designed to plug into them.

Table 3.10. CPU Socket Specifications
Chip Class Socket Pins Layout Voltage Supported Processors Introduced
486 Socket 1 169 17×17 PGA 5V 486 SX/SX2, DX/DX2, DX4 OD Apr. 1989
Socket 2 238 19×19 PGA 5V 486 SX/SX2, DX/DX2, DX4 OD, 486 Pentium OD Mar. 1992
Socket 3 237 19×19 PGA 5V/3.3V 486 SX/SX2, DX/DX2, DX4, 486 Pentium OD, AMD 5x86 Feb. 1994
Socket 6[1] 235 19×19 PGA 3.3V 486 DX4, 486 Pentium OD Feb. 1994
586 Socket 4 273 21×21 PGA 5V Pentium 60/66, OD Mar. 1993
Socket 5 320 37×37 SPGA 3.3V/3.5V Pentium 75-133, OD Mar. 1994
Socket 7 321 37×37 SPGA VRM Intel Pentium 75-233+, MMX, OD, AMD K5/K6, Cyrix M1/II Jan. 1997
686 Socket 8 387 Dual-pattern SPGA Auto VRM Intel Pentium Pro, OD Nov. 1995
Slot 1 (SC242) 242 Slot Auto VRM Intel Pentium II/III SECC, Celeron SEPP May 1997
Socket 370 370 37×37 SPGA Auto VRM Intel Celeron/Pentium III PPGA/FC-PGA, VIA/Cyrix III/C3 Nov. 1998
Intel P4/Core Socket 423 423 39×39 SPGA Auto VRM Intel Pentium 4 FC-PGA Nov. 2000
Socket 478 478 26×26 mPGA Auto VRM Intel Pentium 4/Celeron FC-PGA2, Celeron D Oct. 2001
Socket T (LGA775) 775 30×33 LGA Auto VRM Intel Pentium 4/Extreme Edition, Pentium D, Celeron D, Pentium dual-core, Core2 June 2004
LGA1156 (Socket H) 1156 40×40 LGA Auto VRM Intel Pentium, Core i3/i5/i7, Xeon Sept. 2009
LGA1366 (Socket B) 1366 41×43 LGA Auto VRM Intel Core i7, Xeon Nov. 2008
LGA1155 (Socket H2) 1155 40×40 LGA Auto VRM Intel Core i7, i5, i3 Jan. 2011
AMD K7 class Slot A 242 Slot Auto VRM AMD Athlon SECC June 1999
Socket A (462) 462 37×37 SPGA Auto VRM AMD Athlon/Athlon XP/Duron PGA/FC-PGA June 2000
AMD K8 class Socket 754 754 29×29 mPGA Auto VRM AMD Athlon 64 Sep. 2003
Socket 939 939 31×31 mPGA Auto VRM AMD Athlon 64 v.2 June 2004
Socket 940 940 31×31 mPGA Auto VRM AMD Athlon 64 FX, Opteron Apr.2003
Socket AM2 940 31×31 mPGA Auto VRM AMD Athlon 64/64FX/64 X2, Sempron, Opteron, Phenom May 2006
Socket AM2+ 940 31×31 mPGA Auto VRM AMD Athlon 64/64 X2, Opteron, Phenom X2/X3/X4. II X4 Nov. 2007
Socket AM3 941[2] 31×31 mPGA Auto VRM AMD Athlon II, Phenom II, Sempron Feb. 2009
Socket AM3+ 941[2] 31×31 mPGA Auto VRM AMD “Bulldozer” processors Mid-2011 (expected)
Socket F (1207 FX) 1207 35×35 LGA Auto VRM AMD Athlon 64 FX, Opteron Aug. 2006
Server/Workstation Slot 2 (SC330) 330 Slot Auto VRM Intel Pentium II/III Xeon Apr. 1998
Socket 603 603 31×25 mPGA Auto VRM Intel Xeon (P4) May 2001
Socket 604 604 31×25 mPGA Auto VRM Intel Xeon (P4) Oct. 2003
Socket PAC418 418 38×22 split SPGA Auto VRM Intel Itanium May 2001
Socket PAC611 611 25×28 mPGA Auto VRM Itanium 2 July 2002
LGA771 (Socket J) 771 30×33 LGA Auto VRM Intel Xeon Jun. 2006
Socket M (PGA478MT) 478 26×26 PGA Auto VRM Intel Xeon Jan. 2006
LGA1567 1567 38×43 LGA Auto VRM Intel Xeon April 2011
Socket 940 940 31×31 mPGA Auto VRM AMD Athlon 64 FX, Opteron Apr. 2003
Socket F (1207 FX) 1207 35×35 LGA Auto VRM AMD Athlon 64 FX, Opteron Aug. 2006
FC-PGA = Flip-chip pin grid array FC-PGA2 = FC-PGA with an integrated heat spreader (IHS) LGA = Land grid array
OverDrive = Retail upgrade processors PAC = Pin array cartridge
PGA = Pin grid array PPGA = Plastic pin grid array
SECC = Single edge contact cartridge SEPP = Single edge processor package
SPGA = Staggered pin grid array mPGA = Micro pin grid array
VRM = Voltage regulator module with variable voltage output determined by module type or manual jumpers Auto VRM = Voltage regulator module with automatic voltage selection determined by processor voltage ID (VID) pins

[1] Socket 6 was never actually implemented in systems.

[2] Socket has 941 pins, but CPUs for Socket AM3 have 938 pins.

Sockets 1, 2, 3, and 6 are 486 processor sockets and are shown together in Figure 3.7 so you can see the overall size comparisons and pin arrangements between these sockets. Sockets 4, 5, 7, and 8 are Pentium and Pentium Pro processor sockets and are shown together in Figure 3.8 so you can see the overall size comparisons and pin arrangements between these sockets.

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Figure 3.7. 486 processor sockets.
Figure 3.8. Pentium and Pentium Pro processor sockets.

When the Socket 1 specification was created, manufacturers realized that if users were going to upgrade processors, they had to make the process easier. The socket manufacturers found that 100 lbs. of insertion force is required to install a chip in a standard 169-pin Socket 1 motherboard. With this much force involved, you easily could damage either the chip or the socket during removal or reinstallation. Because of this, some motherboard manufacturers began using low insertion force (LIF) sockets, which required a smaller 60 lbs. of insertion force for a 169-pin chip. Pressing down on the motherboard with 60–100 lbs. of force can crack the board if it is not supported properly. A special tool is also required to remove a chip from one of these sockets. As you can imagine, even the LIF was relative, and a better solution was needed if the average person was ever going to replace his CPU.

Manufacturers began using ZIF sockets in Socket 1 designs, and all processor sockets from Socket 2 and higher have been of the ZIF design. ZIF is required for all the higher-density sockets because the insertion force would simply be too great otherwise. ZIF sockets almost eliminate the risk involved in installing or removing a processor because no insertion force is necessary to install the chip and no tool is needed to extract one. Most ZIF sockets are handle-actuated: You lift the handle, drop the chip into the socket, and then close the handle. This design makes installing or removing a processor easy.

The following sections take a closer look at those socket designs you are likely to encounter in active PCs.

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Socket 478

Socket 478 is a ZIF-type socket for the Pentium 4 and Celeron 4 (Celerons based on the Pentium 4 core) introduced in October 2001. It was specially designed to support additional pins for future Pentium 4 processors and speeds over 2GHz. The heatsink mounting is different from the previous Socket 423, allowing larger heatsinks to be attached to the CPU. Figure 3.9 shows Socket 478.

Figure 3.9. Socket 478 (Pentium 4) showing pin 1 location.

Socket 478 supports a 400MHz, 533MHz, or 800MHz processor bus that connects the processor to the MCH, which is the main part of the motherboard chipset.

Socket 478 uses a heatsink attachment method that clips the heatsink directly to the motherboard, and not the CPU socket or chassis (as with Socket 423). Therefore, any standard chassis can be used, and the special standoffs used by Socket 423 boards are not required. This heatsink attachment allows for a much greater clamping load between the heatsink and processor, which aids cooling.

Socket 478 processors use five VID pins to signal the VRM built into the motherboard to deliver the correct voltage for the particular CPU you install. This makes the voltage selection completely automatic and foolproof. A small triangular mark indicates the pin-1 corner for proper orientation of the chip.

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Socket LGA775

Socket LGA775 (also called Socket T) is used by the Core 2 Duo/Quad processors, the latest versions of the Intel Pentium 4 Prescott processor and the Pentium D and Pentium Extreme Edition processors. Some versions of the Celeron and Celeron D also use Socket LGA775. Socket LGA775, unlike earlier Intel processor sockets, uses a land grid array format, so the pins are on the socket, rather than the processor.

LGA uses gold pads (called lands) on the bottom of the processor to replace the pins used in PGA packages. It allows for much greater clamping forces via a load plate with a locking lever, with greater stability and improved thermal transfer (better cooling). The first LGA processors were the Pentium II and Celeron processors in 1997; in those processors, an LGA chip was soldered on the Slot-1 cartridge. LGA is a recycled version of what was previously called leadless chip carrier (LCC) packaging. This was used way back on the 286 processor in 1984, and it had gold lands around the edge only. (There were far fewer pins back then.) In other ways, LGA is simply a modified version of ball grid array (BGA), with gold lands replacing the solder balls, making it more suitable for socketed (rather than soldered) applications. Socket LGA775 is shown in Figure 3.10.

Figure 3.10. Socket LGA775 (Socket T).

The release lever on the left raises the load plate out of the way to permit the processor to be placed over the contacts.

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Socket LGA1156

Socket LGA1156 (also known as Socket H) was introduced in September 2009 and was designed to support Intel Core i Series processors featuring an integrated chipset north bridge, including a dual-channel DDR3 memory controller and optional integrated graphics. Socket LGA1156 uses a land grid array format, so the pins are on the socket, rather than the processor. Socket LGA1156 is shown in Figure 3.11.

Because the processor includes the chipset north bridge, Socket LGA1156 is designed to interface between a processor and a Platform Controller Hub (PCH), which is the new name used for the south bridge component in supporting 5x series chipsets. The LGA1156 interface includes the following:

  • PCI Express x16 v2.0— For connection to either a single PCIe x16 slot, or two PCIe x8 slots supporting video cards.

  • DMI (Direct Media Interface)— For data transfer between the processor and the PCH. DMI in this case is essentially a modified PCI Express x4 v2.0 connection, with a bandwidth of 2GBps.

  • DDR3 dual-channel— For direct connection between the memory controller integrated into the processor and DDR3 SDRAM modules in a dual-channel configuration.

  • FDI (Flexible Display Interface)— For the transfer of digital display data between the (optional) processor integrated graphics and the PCH.

When processors with integrated graphics are used, the Flexible Display Interface carries digital display data from the GPU in the processor to the display interface circuitry in the PCH. Depending on the motherboard, the display interface can support DisplayPort, High Definition Multimedia Interface (HDMI), Digital Visual Interface (DVI), or Video Graphics Array (VGA) connectors.

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Socket LGA1366

Socket LGA1366 (also known as Socket B) was introduced in November 2008 to support high-end Intel Core i Series processors, including an integrated triple-channel DDR3 memory controller, but which also requires an external chipset north bridge, in this case called an I/O Hub (IOH). Socket LGA1366 uses a land grid array format, so the pins are on the socket, rather than the processor. Socket LGA1366 is shown in Figure 3.12.

Figure 3.12. Socket LGA1366 (Socket B).

Socket LGA1366 is designed to interface between a processor and an IOH, which is the new name used for the north bridge component in supporting 5x series chipsets. The LGA1366 interface includes the following:

  • QPI (Quick Path Interconnect)— For data transfer between the processor and the IOH. QPI transfers 2 bytes per cycle at either 4.8 or 6.4GHz, resulting in a bandwidth of 9.6 or 12.8GBps.

  • DDR3 triple-channel— For direct connection between the memory controller integrated into the processor and DDR3 SDRAM modules in a triple-channel configuration.

LGA1366 is designed for high-end PC, workstation, or server use. It supports configurations with multiple processors.

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Socket LGA1155

Socket LGA1155 (also known as Socket H2) was introduced in January 2011 to support Intel’s Sandy Bridge (second-generation) Core i Series processors, which now include Turbo Boost overclocking. Socket LGA1155 uses a land grid array format, so the pins are on the socket, rather than the processor. Socket LGA1155 uses the same cover plate as Socket 1156, but is not interchangeable with it.

Socket LGA1155 is shown in Figure 3.13.

Figure 3.13. Socket LGA1155 (Socket H2) before installing a processor.

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Socket 939 and 940

Socket 939 is used with the Socket 939 versions of the AMD Athlon 64, 64 FX, and 64 X2 (see Figure 3.14). It’s also used by some versions of the AMD Opteron processor for workstations and servers. Motherboards using this socket support conventional unbuffered DDR SDRAM modules in either single- or dual-channel mode, rather than the server-oriented (more expensive) registered modules required by Socket 940 motherboards. Sockets 939 and 940 have different pin arrangements and processors for each and are not interchangeable.

Figure 3.14. Socket 939.
The cutout corner and triangle at the lower left indicate pin 1.

Socket 940 is used with the Socket 940 version of the AMD Athlon 64 FX, as well as most AMD Opteron processors (see Figure 3.15). Motherboards using this socket support only registered DDR SDRAM modules in dual-channel mode. Because the pin arrangement is different, Socket 939 processors do not work in Socket 940, and vice versa.

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Figure 3.15. Socket 940.
The cutout corner and triangle at the lower left indicate pin 1.

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Socket AM2/AM2+/AM3/AM3+

In May 2006, AMD introduced processors that use a new socket, called Socket AM2 (see Figure 3.16). AM2 was the first replacement for the confusing array of Socket 754, Socket 939, and Socket 940 form factors for the Athlon 64, Athlon 64 FX, and Athlon 64 X2 processors.

Figure 3.16. Socket AM2/AM2+.
The arrow (triangle) at the lower left indicates pin 1.

Although Socket AM2 contains 940 pins—the same number that Socket 940 uses—Socket AM2 is designed to support the integrated dual-channel DDR2 memory controllers that were added to the Athlon 64 and Opteron processor families in 2006. Processors designed for Sockets 754, 939, and 940 include DDR memory controllers and are not pin compatible with Socket AM2. Sockets 939, 940, and AM2 support HyperTransport v2.0, which limits most processors to a 1GHz FSB.

Socket AM2+ is an upgrade to Socket AM2 that was released in November 2007. Although Sockets AM2 and AM2+ are physically the same, Socket AM2+ adds support for split power planes and HyperTransport 3.0, allowing for FSB speeds of up to 2.6GHz. Socket AM2+ chips are backward compatible with Socket AM2 motherboards, but only at reduced HyperTransport 2.0 FSB speeds. Socket AM2 processors can technically work in Socket AM2+ motherboards; however, this also requires BIOS support, which is not present in all motherboards.

Socket AM3 was introduced in February 2009, primarily to support processors with integrated DDR3 memory controllers such as the Phenom II. Besides adding support for DDR3 memory, Socket AM3 has 941 pins in a modified key pin configuration that physically prevents Socket AM2 or AM2+ processors from being inserted (see Figure 3.17).

Figure 3.17. Socket AM3.
The arrow (triangle) at the lower left indicates pin 1.

Socket AM3+ is a modified version of AM3 designed for the new “Bulldozer” processors. It has 938 pins, and also supports processors made for AM3 sockets. Table 3.11 shows the essential differences between Socket AM2, AM2+, AM3, and AM3+.

 

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Table 3.11. Socket AM2, AM2+, AM3, and AM3+ Features
Features Socket AM2 Socket AM2+ Socket AM3 Socket AM3+
Number of Pins 940 940 938 938
Hyper-Transport (FSB) Support 2.0 (up to 1.4GHz) 3.0 (up to 2.6GHz) 3.0 (up to 2.6GHz) 3.0 (up to 2.6GHz)
Supported Memory DDR2 (dual-channel) DDR2 (dual-channel) DDR3 (dual-channel) DDR3 (dual-channel)
Supported Processors Socket AM2, AM2+, or AM3 Socket AM2, AM2+, AM3 Socket AM3 Socket AM3+ or AM3

Here is a summary of the compatibility between AM2, AM2+,AM3, and AM3+ processors and motherboards:

  • You cannot install Socket AM2 or AM2+ processors in Socket AM3 motherboards.

  • You can install Socket AM2 processors in Socket AM2+ motherboards.

  • You can install Socket AM3 or AM2+ processors in Socket AM2 motherboards; however, the BIOS must support the processor, the FSB will run at lower HT 2.0 speeds, and only DDR2 memory is supported.

  • You can install Socket AM3 processors in Socket AM2+ motherboards, but the BIOS must support the processor, and only DDR2 memory is supported.

  • You can install Socket AM3 processors in Socket AM3+ motherboards, but the BIOS must support the processor.

Although you can physically install newer processors in motherboards with older sockets, and they should theoretically work with reductions in bus speeds and memory support, this also requires BIOS support in the specific motherboard, which may be lacking. In general, you are best off matching the processor to a motherboard with the same type of socket.

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Socket F (1207FX)

Socket F (also called 1207FX) was introduced by AMD in August 2006 for its Opteron line of server processors. Socket F is AMD’s first land grid array (LGA) socket, similar to Intel’s Socket LGA775. It features 1,207 pins in a 35-by-35 grid, with the pins in the socket instead of on the processor. Socket F normally appears on motherboards in pairs because it is designed to run dual physical processors on a single motherboard. Socket F was utilized by AMD for its Quad FX processors, which are dual-core processors sold in matched pairs, operating as a dual socket dual-core system. Future versions may support quad-core processors, for a total of 8 cores in the system. Due to the high expense of running dual physical processors, only a limited number of nonserver motherboards are available with Socket F.

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