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Slot 1
Chip form factors
FSB protocolAGTL+
FSB frequency66, 100, and (on third-party chipsets) 133 MHz
Voltage range1.3 to 3.50 V
ProcessorsPentium II: 233–450 MHz

Celeron: 266–433 MHz
Pentium III: 450 MHz–1.13 GHz
(A Slotket makes following Socket 370 CPUs usable:
Celeron and Pentium III to 1,400 MHz,
VIA Cyrix III: 350–733 MHz,
VIA C3: 733–1,200 MHz

Slotkets also made it possible to use some Pentium Pro CPUs for Socket 8 using the same method.)
PredecessorSocket 7
SuccessorSocket 370

This article is part of the CPU socket series
Pentium II SECC form installed into Slot 1

Slot 1 refers to the physical and electrical specification for the connector used by some of Intel's microprocessors, including the Pentium Pro, Celeron, Pentium II and the Pentium III. Both single and dual processor configurations were implemented.

Intel reverted back to the traditional socket interface with the release of Socket 370 in 1999.


With the introduction of the Pentium II CPU, the need for greater access for testing had made the transition from socket to slot necessary. Previously with the Pentium Pro, Intel had combined processor and cache dies in the same Socket 8 package. These were connected by a full-speed bus, resulting in significant performance benefits. Unfortunately, this method required that the two components be bonded together early in the production process, before testing was possible. As a result, a single, tiny flaw in either die made it necessary to discard the entire assembly, causing low production yield and high cost.[citation needed]

Intel subsequently designed a circuit board where the CPU and cache remained closely integrated, but were mounted on a printed circuit board, called a Single-Edged Contact Cartridge (SECC). The CPU and cache could be tested separately, before final assembly into a package, reducing cost and making the CPU more attractive to markets other than that of high-end servers. These cards could also be easily plugged into a Slot 1, thereby eliminating the chance for pins of a typical CPU to be bent or broken when installing in a socket.

A Slot A CPU on the left compared to a Slot 1 CPU (connector rotated by 180 degrees)

The form factor used for Slot 1 was a 5-inch-long, 242-contact edge connector named SC242. To prevent the cartridge from being inserted the wrong way, the slot was keyed to allow installation in only one direction. The SC242 was later used for AMD's Slot A as well, and while the two slots were identical mechanically, they were electrically incompatible. To discourage Slot A users from trying to install a Slot 1 CPU, the connector was rotated 180 degrees on Slot A motherboards. This also allowed motherboard manufacturers to save costs by stocking the same part for both Slot 1 and Slot A assemblies.

With the new Slot 1, Intel added support for symmetric multiprocessing (SMP). A maximum of two Pentium II or Pentium III CPUs can be used in a dual slot motherboard. The Celeron does not have official SMP support.

There are also converter cards, known as Slotkets, which hold a Socket 8 so that a Pentium Pro CPU can be used with Slot 1 motherboards.[2] These specific converters, however, are rare. Another kind of slotket allows using a Socket 370 CPU in a Slot 1. These are generally more common than Socket 8 to Slot 1 slotkets. Many of these latter devices are equipped with their own voltage regulator modules, in order to supply the new CPU with a lower core voltage, which the motherboard would not otherwise allow.

Form factors

Intel Pentium II CPU in SECC form factor
Pentium III (Katmai) in SECC2: CPU at center, two chips at right are cache
Celeron in SEPP: CPU at center (under heat spreader), surrounding chips are resistors and bypass capacitors

The Single Edge Contact Cartridge, or "SECC", was used at the beginning of the Slot 1-era for Pentium II CPUs. Inside the cartridge, the CPU itself is enclosed in a hybrid plastic and metal case. The back of the housing is plastic and has several markings on it: the name, "Pentium II"; the Intel logo; a hologram; and the model number. The front consists of a black anodized aluminum plate, which is used to hold the CPU cooler. The SECC form is very solid, because the CPU itself is resting safely inside the case. As compared to socket-based CPUs, there are no pins that can be bent, and the CPU is less likely to be damaged by improper installation of a cooler.

Following SECC, the SEPP-form (Single Edge Processor Package) appeared on the market. It was designed for lower-priced Celeron CPUs. This form lacks a case entirely, consisting solely of the printed-circuit board holding the components.

A form factor called SECC2 was used for late Pentium II and Pentium III CPUs for Slot 1, which was created to accommodate the switch to flip chip packaging.[3] Only the front plate was carried over, the coolers were now mounted straight to the PCB and exposed CPU die and are, as such, incompatible with SECC cartridges.


Historically, there are three platforms for the Intel P6 CPUs: Socket 8, Slot 1 and Socket 370.

Slot 1 is a successor to Socket 8. While the Socket 8 CPUs (Pentium Pro) directly had the L2-cache embedded into the CPU, it is located (outside of the core) on a circuit board shared with the core itself. The exception is later Slot 1 CPUs with the Coppermine core which have the L2-cache embedded into the die.

In the beginning of 2000, around the time the Coppermine Pentium III CPUs with FC-PGA housing were already produced, Slot 1 was slowly succeeded by Socket 370, after Intel had already offered Socket 370 and Slot 1 CPUs at the same time since late 1998. Socket 370 was initially made for low-cost Celeron processors starting with the Mendocino Celerons, while Slot 1 was thought of as a platform for the more expensive Pentium II and early Pentium III models. Both cache and core were embedded into the die.

Slot 1 also obsoleted the old Socket 7, at least regarding Intel, as the standard platform for home users. After superseding the Intel P5 Pentium MMX CPU, Intel completely left the Socket 7 market.

Chipsets and officially supported CPUs

Slot 1/Socket 370 Converter
Slot 1/Socket 8 Converter

Intel 440FX

Intel 440LX

Intel 440EX

Intel 440BX

Intel 440ZX

Intel 810

Intel 820/820E (Camino)

Intel 840

VIA Apollo Pro / Pro II / Pro+

VIA Apollo Pro 133

VIA Apollo Pro 133A

SiS 5600 (SiS 600)

SiS 620

See also


  1. ^ "CPU Sockets Chart". Retrieved 2009-03-31.
  2. ^ "PPro on a BX?-Usenet Gateway". Archived from the original on 2007-09-29.
  3. ^,94-2.html[dead link]
  4. ^ List of Intel chipsets
  5. ^ List of VIA chipsets
  6. ^ Intel Corporation: 440FX PCIset Datasheet
  7. ^ Intel Corporation: 440LX AGPset Design Guide[permanent dead link]
  8. ^ Intel Corporation: 440EX AGPset Design Guide
  9. ^ Intel Corporation: 440BX AGPset Design Guide Archived 2012-10-04 at the Wayback Machine