Rock and APL are not related
The APL agreement between Sun and Fujitsu is unrelated to Sun's Rock processor project.
Sun originally had an UltraSPARC V "Millennium" processor project for its next generation of midrange and high-end servers after UltraSPARC IV+. Sun canceled this project in early 2004 (along with the "Gemini" processor project for low-end servers), to put all of its resources into Rock and Niagara. The goal was to accelerate the time to market for Rock.
The APL agreement was struck in 2004, with the goal of shipping hardware in late 2006. The purpose of the APL project was to provide next-generation, midrange and high-end SPARC/Solaris servers for Sun customers after the final UltraSPARC IV+ speed increases were released.
Realistically, the gap between US-IV+ and Rock would be somewhere between 1.5 and 3 years, and there was no guarantee US-IV+ would be able to ship 1.8 GHz in volume, or exceed 1.8 GHz. Likewise, Rock was a new design approach, and there was no guarantee it could make its target release of 2008. Sun felt this was too much of a risk, and entered the agreement with Fujitsu.
Rock systems are not necessarily direct replacement for APL systems. In 2008, Fujitsu will release the "Jupiter" processor, an improved, faster, quad-core version of the dual-core "Olympus" SPARC64-VI processor. This will double the performance of APL servers, and shift the APL line higher on the performance curve. This long future and investment protection make the APL servers an excellent choice today for customers looking to replace UltraSPARC III and early UltraSPARC IV systems.
For customers who made significant investments in UltraSPARC IV and IV+ gear over the last year or two, and are not likely to replace these systems until 2008 or 2009, Rock may be the preferred replacement platform. However, high-end APL M9000 systems with Jupiter processors may still considered by many customers, especially those who have already invested in APL products. Another factor is the software. Some applications will better perform on fewer, more powerful threads compared to Rock's radical CMT architecture (which is better suited for more modern apps like Java and RDBMS). Note Sun not only continues to sell, but recently upgraded their UltraSPARC IIIi systems, despite the release of the UltraSPARC T1 "Niagara" servers, for the very reason some legacy apps are better suited for the traditional SMP architecture rather than radical CMT.
Sun has always rolled its workstation, low-end server, and mid-range server product line. The UltraSPARC II E3000 was replaced by the E450. At the same time the E3000 was upgraded to the E3500 with more processor sockets to fill a new performance point. The Ultra 1 and Ultra 2 workstations were replaced by the PCI-based Ultra 30 and Ultra 60. The Ultra 30 was replaced with the Ultra 10, at a much lower price point. The UltraSPARC-III Sun Fire 280R and Sun Fire V480 were replaced by the UltraSPARC IIIi V240 and V440. The V480 was upgraded with dual-core UltraSPARC IVs to become the V490, moving up to a new performance point. The eight-socket Sun Fire 3800 was ultimately replaced by the eight-socket V880. The twelve-socket Sun Fire 4800 was joined by the twelve-socket V1280. Sun continues to upgrade and sell both of these twelve socket US-IV+ systems.
This will be no different with Rock and APL. Rock products will come in, and APL products will be upgraded with Jupiter processors and move up into higher performance points. In some cases there will be significant overlap (like the E4900 and E2900 today). If customers continue to buy both systems, Sun will continue to sell both systems.
At the same time the operating system remains the same, and binary compatibility is guaranteed.
Constant refresh, customer choice, and guaranteed compatibility. Sun has been doing it for over 10 years.
It really is a very elegant approach.