Legacy 1GHz Pentium III processor for compatible Slot 1 vintage computers, workstations, and servers. The SL4KL uses the Coppermine core with a 100MHz front-side bus, 256KB of full-speed on-die L2 cache, and the S.E.C.C.2 cartridge package.
Its 100MHz bus makes it especially useful for period-correct 440BX and 440GX restorations where a 133MHz bus would operate outside the chipset’s standard specification. Suitable for vintage gaming systems, collector builds, industrial-computer repair, legacy workstation restoration, and compatible dual-processor platforms.
Direct processor-equivalent identifiers:
SL4KL, SL4BR, 80526PY1000256, BX80526H1000256
Common searchable descriptions and markings:
Pentium III 1000E, Pentium III 1GHz 100MHz FSB, Pentium III 1000/256/100, 1000/256/100/1.70V S1, SC242 1GHz, S.E.C.C.2 1GHz
SL4KL is the boxed-product S-Spec associated with an attached fan-heatsink. SL4BR is the tray/OEM S-Spec for the same cC0, 1GHz, 100MHz-bus, 256KB S.E.C.C.2 processor configuration.
SL4BS is intentionally excluded. Although it is also a 1GHz Slot 1 processor, it uses a 133MHz bus and a 7.5x multiplier rather than the SL4KL’s 100MHz bus and 10x multiplier.
QY01 is an engineering-sample reference and is not included as a standard production replacement.
When reinstalling or servicing the processor’s fan-heatsink assembly, use Shin-Etsu G751 High-Performance Thermal Grease to renew the thermal interface between the processor and heatsink.
Thermal compound is sold separately.
Please note that this list is not exhaustive. A Slot 1 connector alone does not confirm compatibility. The motherboard must support a 1GHz, 100MHz-FSB, 1.70V Coppermine processor with cC0 microcode. Verify the motherboard revision, BIOS version, voltage regulator, retention mechanism, and available heatsink clearance before ordering.
✔️ Direct Intel-Validated Platform: Intel Server Board L440GX+
✔️ ASUS 440BX Motherboards: P3B-F PCB revision 1.04 or newer with BIOS 1008.001 or newer; P2B-B PCB revision 1.02 or newer with BIOS 1013.006 or newer
✔️ ASUS P3B-1394: All PCB revisions with BIOS 2004.001 or newer
✔️ ASUS P3W: All PCB revisions with BIOS 1016.004 or newer
✔️ ASUS P3C-L: All PCB revisions; officially listed for the 1GHz Slot 1 processor
✔️ ASUS P3C Series: P3C-E, P3C-D, P3C-S, and P3C-LS with BIOS 1025.001 or newer
✔️ ASUS P3C2000: All PCB revisions with BIOS 1025.001 or newer
✔️ ASUS P3V133: All PCB revisions with BIOS 1003.001 or newer
✔️ Compatible Dual-Processor Platforms: Intel L440GX+ and ASUS P3C-D configurations supporting two 1GHz Slot 1 processors; a matched processor pair is strongly recommended
✔️ General Slot 1 Platform Support: Late-revision Slot 1 motherboards that explicitly list support for a Pentium III 1.0GHz—not only the 1.0B GHz version—and can supply the required 1.70V Coppermine core voltage
✔️ Typical Legacy Operating Environments: Windows 98, Windows 98 SE, Windows Me, Windows NT 4.0, Windows 2000, and compatible legacy Linux or UNIX distributions when the complete system has suitable drivers
☑️ High-end 1GHz processor for compatible vintage Slot 1 systems
☑️ 100MHz front-side bus suitable for in-spec 440BX and 440GX operation
☑️ 256KB full-speed on-die Advanced Transfer Cache
☑️ 32KB integrated L1 cache
☑️ cC0 Coppermine core operating at 1.70V
☑️ S.E.C.C.2 cartridge installs directly into a compatible Slot 1 connector
☑️ MMX and SSE instruction support for period multimedia and 3D applications
☑️ Supports compatible single- and dual-processor platforms
☑️ Direct processor-equivalent replacement for SL4BR
☑️ Useful for vintage gaming, workstation restoration, industrial repair, and collecting
☑️ Retains the standard 100MHz chipset bus while achieving a 1GHz core speed
☑️ Factory-locked 10x multiplier provides the correct 1GHz operating frequency from a 100MHz bus
✓ This is a Slot 1 / SC242 S.E.C.C.2 processor. It is not compatible with Socket 370, Slot A, Socket 7, or later processor sockets.
✓ Physical Slot 1 fit does not guarantee operation. The motherboard must support 1.70V Coppermine processors, the cC0 stepping, and a 1GHz/100MHz configuration.
✓ Install the required BIOS revision before removing the system’s currently supported processor whenever possible.
✓ Do not substitute SL4BS without checking the motherboard. SL4BS is the different 133MHz-bus version.
✓ A compatible fan-heatsink and functioning fan connection are required. Confirm the cooling hardware included with the actual item before ordering.
✓ The motherboard and chassis must have the correct Slot 1 retention mechanism and adequate clearance for the S.E.C.C.2 cartridge and cooling assembly.
✓ For dual-processor systems, use two processors with matching speed, bus, cache size, and preferably the same S-Spec and stepping.
✓ Disconnect power and follow suitable ESD precautions during installation. Renew the thermal compound if the heatsink is removed.
