This CPU is primarily a collector's item for retro computing enthusiasts. It is an AMD Athlon A1200AMS3C is a classic desktop processor from the "Thunderbird" era (Model 4). Launched in late 2000, it was a high-end chip for its time, notable for being one of the first to feature on-die, full-speed L2 cache, which significantly boosted performance over earlier models.
For buyers, this is an excellent choice for a late-90s/early-2000s Windows 98 SE gaming build, as the 266 MHz FSB version ("C" suffix) provides a noticeable speed boost over the 200 MHz ("B" suffix) variant.
The included "fiber mask" or "spacer" is the CPU Shim (also commonly called a CPU Spacer) and has rarely been preserved with these CPUs.
For the AMD Athlon 1.2GHz (A1200AMS3C), which uses the Thunderbird core, this component was a critical safety accessory. Unlike modern CPUs that have an Integrated Heat Spreader (IHS)—the silver metal lid you see on top—these older Athlons had a "naked" or exposed ceramic silicon die.
The shim was designed to solve two major problems with the Socket A (Socket 462) platform:
Die Protection: The silicon die on the Athlon was extremely brittle. Because the heatsink mounting clips required significant force to snap into place, the heatsink could easily "tilt" during installation, crushing the corners of the die and permanently destroying the CPU.
Stability: The shim sat around the die, acting as a level platform for the heatsink to rest on, ensuring even pressure across the entire surface.
CPU Specifications;

As a note, at its launch in October 2000, this processor had an MSRP of roughly $673 USD.
Descriptions are derived from AI generated info.
The CPU has the components checked under a microscope. Pins are straight. It has been carefully cleaned; minor amounts of thermal paste may be present.
See our other sales for different quantities of other CPUs and RAM. Thank you for your interest.