Processor Socket and Slot Types

Overview of x86 and Itanium Server Processor and Socket 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 2.14 shows the specifications of sockets used for x86 and Itanium server processors, starting with the Intel Pentium Pro.

Table 2.14. x86 and Itanium CPU Socket and Slot Types and Specifications ^[1]

^[1] Key: FC-PGA = flip-chip pin grid array; FC-PGA2 = FC-PGA with an Integrated Heat Spreader; OD = OverDrive (retail upgrade processors); PAC = pin array cartridge; PGA = pin grid array; PPGA = plastic pin grid array; SC242 = slot connector, 242 pins; SC330 = slot connector, 330 pins; SECC = single-edge contact cartridge; 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 ; and Auto VRM = voltage regulator module with automatic voltage selection determined by processor voltage ID (VID) pins.

Packaging

The most common packaging type used for x86 and RISC-based processors over the past decade has been the pin grid array (PGA) design. PGA can be subdivided into several categories, reflecting advances in processor design and the never-ending quest for better cooling.

Other types of processor packaging include ball grid array (BGA) and land grid array (LGA), which are used as alternatives to PGA in some of the most recent processor designs.

Older x86 as well as Itanium and RISC processors also used various types of processor cartridges, which incorporate the processor itself and external cache memory. While x86 processors no longer use processor cartridges, some types of RISC and Itanium-based systems still use subassemblies that incorporate large amounts of cache and the processor. In some cases, a processor cartridge might incorporate two separate processors. The following sections provide details about the major types of processor packaging used on servers.

PGA and PGA Variations

PGA, which dates back to the IBM 286 processor first introduced in 1984, takes its name from the fact that the chip has a grid-like array of pins on the bottom of the package. PGA chips are inserted into sockets, which are often of a zero insertion force (ZIF) design. A ZIF socket has a lever to allow for easy installation and removal of the chip. As Figure 2.9 illustrates, PGA designs can be used for modules that contain the processor and external cache as well as for individual processors (compare Figure 2.9 to Figures 2.10 and 2.11). Figure 2.9 illustrates the front and rear view of a PGA-based processor module, the PowerPC 750.

Depending on the processor, the pins might be in standard rows and columns , as in Figure 2.9 and Figure 2.11, or might be staggered. This type of design is known as staggered PGA (SPGA). This design moves the pins closer together and decreases the overall size of the chip when a large number of pins is required. Figure 2.10 illustrates the SPGA design used by the AMD Athlon MP processor.

Several methods have been used to build PGA chips. Older PGA variations had the processor die mounted in a cavity underneath the substrate, with the top surface facing up if you turned the chip upside-down. The die was then wire-bonded to the chip package, with hundreds of tiny gold wires connecting the connections at the edge of the chip with the internal connections in the package. After the wire bonding, the cavity was sealed with a metal cover. This was an expensive and time-consuming method of producing chips, so less expensive and more efficient packaging methods were designed.

More modern processors are built on a form of flip-chip PGA (FC-PGA) packaging. This type still plugs in to a PGA socket, but the package itself is dramatically simplified. With FC-PGA, the raw silicon die is mounted facedown on the top of the chip substrate, and instead of wire bonding, the connections are made with tiny solder bumps around the perimeter of the die. The edge is then sealed with a fillet of epoxy . With the original versions of FC-PGA, you could see the backside of the raw die sitting on the chip. The Athlon MP chip shown in Figure 2.10 uses an FC-PGA design.

Unfortunately, there were some problems with attaching the heatsink to an FC-PGA chip such as an Intel Pentium III or AMD Athlon MP. The heatsink sat on the top of the die, which acted as a pedestal. If you pressed down on one side of the heatsink excessively during the installation process (such as when you were attaching the clip), you risked cracking the silicon die and destroying the chip. This was especially a problem as heatsinks became larger and heavier and the force applied by the clip became greater.

AMD decreased the risk of damage to the AMD Athlon MP and similar chips by adding rubber spacers to each corner of the chip substrate (as shown in Figure 2.10), thus preventing the heatsink from tilting excessively during installation. Still, these bumpers could compress, and it was too easy to crack the die during heatsink installation.

Intel revised its packaging with a newer FC-PGA2 version used in the newer Pentium III and all Pentium 4 and Xeon processors. It incorporates an integrated protective metal cap called a heat spreader that sits on top of the die, enabling larger and heavier heatsinks to be installed without any potential damage to the processor core . Ironically, the first processor for PCs to use a heat spreader was made by AMD (the K6 family). AMD has returned to the heat spreader design with its Opteron processors.

Figure 2.11 illustrates the FC-PGA2 packaging used by the Intel Xeon DP processor.

AMD Opteron, Intel Xeon, and Intel Pentium 4 processors also use various types of heatsink supports rather than fastening the heatsink directly to the processor socket. This helps prevent damage to the processor.

In addition to changes in the socket and arrangement of the processor core, PGA-based designs have also used various materials for the processor chip substrate. Ceramic material was common for several years , but more recent designs have used lighter-weight plastics, including some organic plastics.

Starting in the late 1990s, some processors began to use a different type of connection known as a BGA. BGA chips use small solder balls to make the connection to the socket. BGA is also used to attach DDR and newer types of memory chips to DIMM modules or graphics cards. Typically, BGA is used when chips are soldered into place, such as on a processor module, as shown in Figure 2.9.

A variation on BGA known as LGA is used by processors that use Socket 775, such as the latest version of the Intel Pentium 4, as well as the new Pentium D and Pentium Extreme Edition. LGA uses gold pads (called lands ) on the bottom of the substrate to replace the pins used in PGA packages or the solder balls used in BGA. In socketed form, LGA allows for much greater clamping forces and therefore greater stability and improved thermal transfer (better cooling) than PGA.

Figure 2.12 illustrates the front and rear of the Pentium D, which uses an LGA design.

Note

Although RISC-based processors typically use PGA or BGA designs, the socket is usually on a small board that also contains cache memory chips. The processor assembly is then plugged in to a slot in the server.

Single-Edge Contact Cartridge Packaging

Intel used cartridge- or board-based packaging for several of its server-class processors from 1997 through 2000. This packaging was called single-edge contact cartridge (SECC), and it consisted of the CPU and separate L2 cache chips mounted on a circuit board that looked similar to an oversized memory module and that plugged in to a slot. In some cases, the boards were covered with plastic cartridge covers.

Building the processor into a cartridge was a cost-effective method for integrating L2 cache into the processor before it was feasible to include the cache directly inside the processor die.

Intel used two types of slots for its server-class processors:

• Slot 1 was used by the Pentium II and by slot-based versions of the Pentium III. (The Pentium III was also available in a FC-PGA socket form factor.)

• Slot 2 was used by the Pentium II Xeon and Pentium III Xeon processors.

Slot 1 was also known as Slot 242, for the 242 pins in the slot connector. The connector used two different- sized sections to prevent incorrect insertion of the cartridge (see Figure 2.13). A rigid or folding frame known as a processor-retention mechanism was used to support the processor. Slot 1 supported single or two-way processor configurations.

Slot 2 was a more sophisticated 330-pin slot designed for the Pentium II Xeon and Pentium III Xeon processors manufactured for servers and workstations. Slot 2 supported up to four-way processing. Note that Slot 2 was also called SC330, which stands for slot connector with 330 pins (see Figure 2.14).

Intel later discovered less-expensive ways to integrate L2 cache into the processor core, and it no longer produces Slot 1 or Slot 2 processors. Both Slot 1 and Slot 2 processors are now obsolete, and most systems using these processors have been retired or upgraded with socket-based motherboards.

Slot 1 (SECC and SECC2) Packaging

Originally, the SECC package wrapped around three sides of the processor cartridge assembly. However, this design made cooling difficult and raised the cost of the processor. Later versions of the Pentium II and all slot-based versions of the Pentium III used a simplified one-piece design known as SECC2.

Figure 2.15 illustrates the SECC2 design. The rectangular chips on the right side of the rear view are the cache memory chips. Note the large thermal plate used to aid in dissipating the heat from this processor. A passive or active heatsink was attached to the thermal plate. The SECC2 design used a different type of retention mechanism (the universal retention system) than the original SECC design that also worked with SECC processors.

Slot 2 Packaging

The Pentium II Xeon and Pentium III Xeon processors are designed in a cartridge similar to but larger than that used for the standard Pentium II/III. Figure 2.16 shows the Xeon cartridge.

Slot 2 versions of the Pentium II Xeon and Pentium III Xeon differ from the standard Pentium II and slot-based Pentium III mainly by virtue of having full-corespeed L2 cache, and in some versions, a larger amount of it. The additional pins allow for additional signals needed by multiple processors.

ZIF Sockets

When the Socket 1 specification used by the first 486 processors 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 pounds of insertion force is required to install a chip in a standard 169-pin screw Socket 1 motherboard. With this much force involved, you could easily damage either the chip or the socket during removal or reinstallation. Therefore, some motherboard manufacturers began using low insertion force (LIF) sockets, which required only 60 pounds of insertion force for a 169-pin chip. But pressing down on the motherboard with 60 to 100 pounds of force can still 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 relatively difficult to work with, and a better solution was needed if the average person was ever going to replace his or her 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 an easy task.

Note

Although removing a processor from a ZIF socket is simple, it is necessary to remove the heatsink from the processor before the processor itself can be removed. If the heatsink has a fan, it must be disconnected from the motherboard or other power source as well. Heatsinks for some processor types clip directly to the processor socket, and if the spring-loaded arm holding the heatsink is not released properly, the socket can be damaged. Socket 478, Socket 603/604, Socket 754, and Sockets 939 and 940 use heatsinks that are mounted on external supports, making installation and removal easier and safer.

Socket 8

Socket 8 is an SPGA socket that features 387 pins that was specifically designed for the Pentium Pro processor with integrated L2 cache. The additional pins enable the chipset to control the L2 cache integrated in the same package as the processor. Figure 2.17 shows the Socket 8 pinout.

Note

The Pentium Pro's Socket 8 is electrically compatible with Slot 1. Consequently, both Intel and third-party vendors such as PowerLeap developed Pentium IIbased upgrades for Pentium Probased systems. These upgrades are no longer being manufactured.

Socket 370

In January 1999, Intel introduced a new socket for P6-class processors. The socket was called Socket 370, or PGA-370, because it has 370 pins and was originally designed for lower-cost PGA versions of the Celeron and Pentium III processors. Socket 370 was originally designed to directly compete in the lower-end system market, along with the Super7 platform supported by AMD and Cyrix. However, Intel later used it for the Pentium III processor, starting in late 1999. This was possible because Intel developed improved processor designs that incorporated L2 cache in the processor core while maintaining high chip yields and low manufacturing costs. By incorporating L2 cache into the processor core, Intel was able to abandon the bulky cartridge design it used for the Pentium II and early Pentium III versions. Socket 370 versions of the Pentium III use an FC-PGA design, in which the raw die is mounted on the substrate upside-down.

The Socket 370 (PGA-370) pinout is shown in Figure 2.18.

The last versions of the Pentium III use the Tualatin core design, which requires a revised socket to operate . Motherboards that can handle Tualatin-core processors are sometimes known as Tualatin-ready and use different chipsets from those not designed to work with the Tualatin-core processor. If you need to replace a Pentium III processor on a Socket 370 server motherboard, make sure you determine what versions of the Pentium III the board can handle. See the vendor documentation for the system or motherboard for details.

Tip

The maximum speed of the Tualatin-core Pentium III processor is 1.4GHz. Some vendors refer to their Tualatin-compatible motherboards as supporting up to 1.4GHz processors.