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There is no single fastest 300 MHz processor for every task. Period testing shows the AMD K6-2 300 was competitive or faster in several integer and 3D workloads, while Intel’s P6-based designs generally had the advantage in floating-point-heavy work. The K6-III can change cache-sensitive results with its full-speed on-chip L2 cache. Because no retrieved review tested an exact K6-2 300, Pentium MMX, Celeron and K6-III together under identical conditions, the fairest answer is workload-specific rather than one overall crown.
First, identify which “300 MHz” chips you mean
Names from this era hide important hardware differences. The original Intel Celeron 300, code-named Covington, had no on-chip L2 cache. The Celeron 300A, code-named Mendocino, ran at the same nominal clock but added 128 KB of on-die L2 cache. Treating those two as the same processor produces misleading conclusions.
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The AMD K6-2 300 is a Socket 7/Super Socket 7-era chip with 3DNow! support. The K6-III added 256 KB of L2 cache on the processor itself; that cache ran at full CPU speed, while compatible motherboard cache could continue to act as an L3 cache. The title’s “Intel MMX” reference normally points to the Pentium MMX family, but a standard retail 300 MHz Pentium MMX configuration was not established in the available period evidence. It should therefore be treated as a comparison target, not as a verified normal retail model.
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A January 11, 1999 Hardware.fr comparison tested K6-2 and Celeron A systems alongside Pentium II systems using Windows 98, DirectX 6, 64 MB of PC100 SDRAM, FIC PA-2013 and ABIT BH6 motherboards, and Voodoo3-era graphics hardware. Its tests included CPU Mark 32, Bryce 3D, MP3 encoding, NaturallySpeaking, Quake II and Half-Life. The K6-2 performed strongly in integer-oriented CPU Mark 32 and NaturallySpeaking. Floating-point results favored the Intel chips in that set. In some 3D Winbench and Quake II cases, the K6-2 reached Pentium II-level or better performance when the software made effective use of 3DNow!.
#1 Best Overall
That condition matters. MMX accelerates integer SIMD operations; it does not provide floating-point SIMD. AMD’s 3DNow! adds SIMD floating-point operations, but a program must explicitly support the instruction set to benefit. A software-rendered game, a 3DNow!-optimized game and a hardware-accelerated game can therefore produce different rankings even at the same clock speed.
Published K6-2 300 and Celeron 300A scores
The following figures are attributed to the Ziff-Davis Testing and Analysis Group and reproduced in an IDT/Centaur benchmark document. They are useful comparisons, but the bus configuration is part of each result.
Rank #2
| Processor and configuration | Winstone 99 | 3D WinMark 99 |
|---|---|---|
| AMD K6-2 300, 4.5 × 66 MHz | 14.9 | 419 |
| AMD K6-2 300, 3 × 100 MHz | 15.0 | 444 |
| Intel Celeron 300A, 4.5 × 66 MHz | 14.8 | 279 |
The K6-2’s two scores show why “300 MHz” alone is incomplete. Both configurations reach 300 MHz, but the 100 MHz front-side bus produces different results from the 66 MHz bus. The table does not prove that the K6-2 wins every benchmark, nor that another motherboard would reproduce the same ordering.
How each design behaves by workload
Integer-heavy applications
The K6-2 was often a strong value performer in integer-oriented work. Hardware.fr reported good CPU Mark 32 and NaturallySpeaking results, and the Ziff-Davis Winstone figures above place the K6-2 300 fractionally ahead of the Celeron 300A in that particular test setup.
Rank #3
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- Cooler not included
Floating-point rendering and scientific work
Intel’s P6-family floating-point unit was more capable in heavily floating-point workloads than the K6’s conventional FPU. Hardware.fr’s Bryce 3D and related results favored the Intel processors in the compared group. A K6-2 can narrow the gap only when the application uses 3DNow! or another supported acceleration path; ordinary floating-point code does not automatically receive that benefit.
Games and 3D
3DNow! can materially help a K6-2 in a game or 3D benchmark that supports it. Hardware.fr found cases in Quake II and 3D Winbench where the K6-2 matched or exceeded Pentium II-level performance under effective 3DNow! use. Those results should not be generalized to every title. Rendering mode, graphics card, driver, API and whether the game uses software rendering all affect the bottleneck.
Rank #4
- Multi-Core: Six-core
- Operating Frequency: 3.2GHz/3.6GHz Turbo Core
- Socket: AM3
- L3 Cache: 6MB
- Power: 125W
Cache-sensitive applications
Cache capacity and latency can matter as much as clock speed. The cacheless Covington Celeron 300 is at a serious disadvantage in many desktop workloads compared with the 300A’s 128 KB on-die cache. The K6-III goes further with 256 KB of on-chip L2 running at CPU speed. Ars Technica described this as an on-chip L2 cache familiar from Intel’s newer Celerons. On a suitable motherboard, the existing external cache can serve as L3, giving the K6-III a different memory hierarchy from the K6-2.
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsAnandTech’s consumer-application discussion provides another example: it attributed a Celeron lag in one NaturallySpeaking test to the smaller L2 cache and noted advantages when software used 3DNow! or SSE. That page covered a broader processor range, not a controlled four-way 300 MHz comparison.
Best Value
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- Quad Core CPU
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So which one should be called fastest?
- Best-supported answer for integer and some 3D work: the AMD K6-2 300 is highly competitive, especially in a 3 × 100 MHz Super Socket 7 configuration and in software that uses 3DNow!.
- Best candidate for floating-point-heavy work: Intel’s P6-derived processors, including the Celeron 300A in the available comparisons, generally have the stronger floating-point execution path.
- Most interesting cache-focused design: the K6-III, because its 256 KB full-speed on-chip L2 can substantially improve cache-sensitive workloads. A specific K6-III 300 result was not supplied, so it cannot be awarded a measured overall win here.
- Weakest version to avoid confusing with the 300A: the original cacheless Celeron 300.
- Pentium MMX: useful as a historical comparison point, but the evidence here does not verify a normal retail 300 MHz model or provide a matched score for one.
What a fair retro-PC comparison must control
- Confirm the exact processor marking, especially Celeron 300 versus Celeron 300A and K6-2 versus K6-III.
- Record multiplier and front-side bus. A 300 MHz K6-2 at 4.5 × 66 MHz is not the same platform configuration as one at 3 × 100 MHz.
- Use the same motherboard class, BIOS settings, RAM, graphics card, driver, operating system and DirectX version.
- Separate integer, floating-point, cache-sensitive and game tests instead of averaging unlike workloads into one score.
- For games, state whether rendering is software-based or accelerated and whether the executable supports MMX or 3DNow!.
Without those controls, a “fastest 300 MHz CPU” claim often measures the motherboard, cache arrangement or software path as much as the processor.
Bottom line for the four-way question
The AMD K6-2 300 is not a universal winner, but it is a credible fastest choice for integer-oriented software and selected 3DNow!-optimized games. Intel’s P6 architecture remains the safer pick for floating-point-heavy work. The K6-III’s 256 KB full-speed L2 gives it the strongest cache-based design, yet the available evidence does not include a controlled exact-300 MHz K6-III result. Most importantly, never lump the cacheless Celeron 300 together with the 128 KB-cache Celeron 300A, and do not treat MHz as a complete performance specification.
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