X86-Secret : ES Zone
Athlon 550 MHz QS  (Week 26, Year 1999)   
AMD-K7550MTR51B C / 219926003463

One of the latest qualification sample of the first Athlon, clocked at 500 MHz. Qualification sample of these processors had a "7th generation processor" marking on the top. The brand "Athlon" wasn't clearly defined at this time. This sample was produced the week of the official launch, in late June.