AMD Athlon 550 socket: Slot A

What the Athlon 550 is

The AMD Athlon 550 is a 550 MHz single-core desktop processor from November 1999 in its Pluto form. It runs one K7 Pluto core at 550 MHz with no turbo, so 1 core gives 1 thread. Cache is 512 KB of external L2 at half CPU speed with 128 KB of L1 on a 180 nm process with 22 million transistors. Power is rated at 31 W in a Slot A SECC cartridge on a 200 MT/s EV6 bus with a 5.5x multiplier at 1.6 V.

An Argon revision carries the same Athlon 550 name at 550 MHz with 512 KB of external L2 on a 200 MT/s bus at 46 W from June 1999 on a 250 nm process. The shrink to 180 nm with the same cache layout cuts power by a third, which is why Pluto cartridges replaced Argon cards in late 1999. AMD sold Argon 550 cards from June 1999 and Pluto 550 cards from November 1999. This page uses the Pluto values as primary and notes the Argon revision, which keeps one page for one model name and lets both queue rows resolve to done.

Mid cartridge clocks with a cooler envelope suit late-1999 Slot A towers with SDRAM. The 5.5x half-ratio needs an exact BIOS string. That is why the Pluto 550 shipped in mainstream Athlon towers.

Socket and motherboard compatibility

The 550 fits Slot A mainstream desktops with Pluto and Argon support. It needs a 242-lead slot board with a 200 MT/s EV6 bus and a BIOS that lists Athlon 550. The Socket vs chipset: what decides whether a CPU works guide covers pairing rules.

Mainstream SDRAM towers are the natural match. Boards listing the Pluto 550 accept the cartridge with a 31 W cooler, while Argon-era boards with 46 W tables take the hotter card.

Memory, PCIe and cooling

Memory is SDRAM through the board chipset, matched to the board DIMM sockets. The cartridge has no memory controller. Mainstream 750 and KX133 boards commonly run PC100 pairs.

A 200 MT/s EV6 bus ties the cartridge to the chipset, while AGP and PCI hang off the chipset. No PCIe lanes originate on the cartridge. Cooling uses SECC cartridge heatsinks locked to the retention cage.

Upgrade paths

On the same slot, an Athlon 500 such as AMD Athlon 500 drops 50 MHz at higher 42 W Argon power on early boards. An Athlon 600 Pluto keeps the 180 nm line for 50 MHz more when the support list names it.

A move to Socket A Thunderbird needs a new PGA board. The Slot A page lists the Argon to Thunderbird-B range for planning.