Barcelona Architecture: AMD on the Counterattack

Introduction

Over the past several years, Intel has followed an odd path of microprocessor design. On the heels of the success of the P6 core, Intel set two teams in motion - one to work on the NetBurst architecture that would be the foundation of the Pentium 4, and one to work on a low-cost, low power highly integrated core that would eventually be redesigned into the Pentium M. The team eventually charged with designing the Pentium M took a more evolutionary approach building off of the strengths of the P6 architecture, while the NetBurst team preferred a radical departure from Intel's previously most successful architecture at the time.

We all know how this story ends; as NetBurst evolved, so did the underlying architecture of the Pentium M. Dothan was the first tweak of the Pentium M and it was mostly a clean up job to fix some performance issues with the original core. Higher clock speeds, more cache, and slight increases in IPC were on Dothan's CV.

Intel's Israel Development Center (IDC) then took Dothan and re-architected it to be a native dual core solution, complete with a shared L2 cache, the first of its type for an Intel processor. The Dothan to Yonah progression was far more significant than the move from Banias to Dothan, not just because Yonah was dual core but also because of the many architectural improvements that went into Yonah.

The next step Intel took is one we're all familiar with, and involves the most radical design change of the Pentium M's short lived history; Intel took Yonah and made it wider, deeper, and far more efficient. Out came the Core 2 line of processors and with it, Intel regained the undisputed performance crown it hadn't seen ever since the debut of AMD's Athlon 64.

While many argued that Banias, the first Pentium M core, was merely a modern take on the P6 architecture it's hard to see much in common between today's Core 2 and the 11 year old Pentium Pro. The P6 core was a starting point for a long line of evolution that brought Intel to where it is today.

AMD took a far more conservative approach over the past several years; it all started with the success of the K7 core, effectively a wider, faster, competitor to later versions of Intel's P6 architecture. While one of Intel's teams was busy making radical departures from anything AMD or Intel had done in the past, AMD didn't have the luxury of running two large scale microprocessor projects in tandem. The solution was to take the K7 core and improve on it, rather than taking a risky step in a different direction.

The K8 core was born as an evolution of the K7; with a slightly deeper pipeline, slight architectural improvements and an integrated Northbridge, the K8 was a pretty major evolutionary step for AMD over the K7. In fact, it took the Core 2 Duo to truly outperform the K8 core across the board, although Dothan and Yonah came quite close in certain applications.

AMD had worked on dramatic successors to the K8, rumored to be K9 and K10, but both appeared to be scrapped or at least focus was shifted away from them in favor of a more evolutionary take on the K8 architecture. The main difference here that allowed Intel to catch up to AMD's performance is that while Intel's Pentium 4 team was operating on the usual schedule of a 5-year micro-architecture cycle, the Pentium M team at IDC was updating its architecture every year. Banias, Dothan, Yonah and Merom/Conroe all happened in a period of four years, and during that same time AMD's K8 remained unchanged.

If Intel had continued down the Pentium 4/NetBurst route, sticking to the usual 5-year design cycle would have probably worked just fine for AMD but Intel had the luxury of having two major micro-processor teams working in parallel, one of which had a much better idea. Luckily it would seem that AMD realized it needed to compete with Intel using smaller evolutionary steps every couple of years rather than leaving an architecture relatively untouched for 4 - 5 years and thus the Barcelona project was created. Although it's set to debut around a year after Intel's Core 2 Duo that swiped the performance crown, Barcelona is AMD's best chance at remaining competitive.

Barcelona's window of opportunity is slim, depending mostly on how Intel's transition to 45nm goes. Publicly Intel has stated that its architectural update to Core 2, codenamed Penryn, will begin shipping by the end of 2007. However, current roadmaps show availability at sometime in 2008 with no word on when significant quantities will be available. Should Intel take longer than expected with the move to its 45nm Penryn core, Barcelona's mid-2007 launch on servers and Q3 '07 launch for desktops may come at a relatively quiet time for Intel.