AMD’s legendary K5, its first independently-designed processor, is being removed from the Linux kernel — 4.3-million-transistor chip gets the axe because it lacks Time Stamp Counter (TSC) support, making it a coding burden
Publish Date: 2026-05-10 08:00:00
Source Domain: www.tomshardware.com
AMD’s landmark K5 processor family will no longer be supported by Linux when kernel version 7.2 arrives. The Linux-watchers at Phoronix noticed the forced retirement of the venerable K5 in a recent patch designed to “remove support for TSC-less Pentium variants.” The lack of TSC (Time Stamp Counter) in the K5 apparently makes it a burden for developers to support in the kernel.
The K5 holds a special place in AMD history as the firm’s first independently designed x86 processor. However, it wasn’t a very popular processor as it arrived late, then offered lackluster performance in the competitive environment it joined.
(Image credit: Birdman86)
AMD’s shiny homegrown 4.3M transistor chip featured a “RISC-based internal architecture that decoded x86 instructions into micro-instructions before executing them,” we noted in a 2008 retrospective. However, launch SKUs in 1996 were limited to clocks from 75 MHz to 133 MHz, and, due to being late, Intel’s Pentium line was already faster. AMD still managed to get an edge on the Cyrix 6×86, though.
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As was de rigueur at the time, these AMD K5 chips were sold with a ‘performance rating’ (PR) figure, suggesting an integer performance comparison with an Intel Pentium with the indicated clock speed. For example, a second revision K5 with a 116 MHz clock was marketed as a K5 PR166. Enthusiasts don’t like this kind of obfuscation, even when it is clearly on the surface. We also note that this era marked the introduction of the heatsink and fan as a CPU-partnering necessity.
Intel i486, AMD Elan SoCs, and AMD Geode CPUs also put out to pasture
We reported a month ago that Linux devs had started to remove support for the 37-year-old Intel i486 CPU in patches destined for the Linux 7.1 kernel. That was probably a bigger deal than today’s AMD K5 news, as many more of these processors were sold.
Other lesser-known processor lines have…
