In early 2000 the world was presented with the Athlon 800 with Slot A interface. This Athlon is based on the Orion core and runs it's L2-cache at just 320MHz (2/5th of the clock-frequency on these models). This hurts performance a bit. The later models with the Thunderbird core have half the L2-cache size but run it's cache at full-speed and thus perform better.

For the Orion series the following thumb-rule applies: the faster the CPU-core is the (relatively) slower the L2-cache is. I.e.: an Athlon 700 has a 350MHz L2-cache speed and an Athlon 1000 (Orion-core) has a 333MHz L2-cache speed. > Read more

The first 1GHz chip from AMD wasn't socketed but appeared as this Slot A model. AMD launched the Athlon 500 in August 1999 and continued to raise clockfrequencies up to 1000MHz in March 2000. The 1GHz mark was magical in the days but the chip was expensive and needed good thermal solutions in order to work properly. It was not until faster Athlon's came out and the 1GHz socket A version became cheaper before people started to buy 1GHz chips. In the benchmarks the Athlon 1000 falls behind on the Pentium III 1000/133FSB. AMD still used off-die L2-cache on their Athlons and the L2-cache couldn't run at 1000MHz. AMD used dividers to clock down the L2-cache (1/3th of the clock-frequency in this case) which hurts performance. Check out the performance of the AMD Athlon 1000C (the 'C' model is the 'Thunderbird' with 256KB on-die full-speed cache) which is ahead on the Pentium III 1000. I wonder where the Pentium III 1000 with 100MHz FSB will end-up. The 100MHz FSB is period-correct to this Athlon 1000. The image on the right was shown on the AMD website in summer 2000. It shows that AMD was proud of it's chip and wanted to emphasize that the 1GHz mark was reached.

Because this chip was expensive and quickly succeeded by the socket A model it wasn't sold much. Getting hands on a 1GHz Slot A chip is getting more difficult by the day.
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