The new series of 64-bit microprocessors being produced by AMD embodying their new x86-64 architecture. As opposed to the revolutionary changes towards VLIW and RISC being promoted by Intel's Itanium/Merced architecture, x86-64 is more of an evolutionary change over the venerable IA-32 architecture that has been with us for the past 15 years.
There are two CPUs in AMD's Hammer line that are going to be produced in the very near future (already they have shown demonstration systems at several trade shows like last month's Intel Developer Forum): the Sledgehammer and Clawhammer CPUs. The former is a more powerful system intended for industrial strength server applications and high-end multiprocessor systems, while the latter is a cheaper, less powerful processor planned for mass market use, designed primarily for uniprocessor configurations. Their relationship is akin to that between the present Athlon and Duron microprocessors in that respect. AMD has announced that the release of these processors is imminent, and has given them the brand names Athlon 64 (Clawhammer) and Opteron (Sledgehammer).
The Hammer processors all have 40-bit physical address space, allowing them to easily handle 1 terabyte of RAM and 48 bits of virtual address space, for 256 terabytes of total addressable memory. The architecture has added 8 more integer registers to the traditional 8 in the old IA32 architecture, in addition to extending the registers to 64 bit width, and has support for SSE and SSE-II floating point instructions.
The processors have an integrated memory controller capable of interfacing to DDR SDRAM and RDRAM easily, which is supposed to reduce latency on memory accesses significantly. The Hammer processors also include HyperTransport technology, providing high-speed, low latency point-to-point links. The Athlon 64 (Clawhammer) is supposed to have a single HyperTransport link with a bandwidth of 6.4 gigabytes/sec, while the Opteron (Sledgehammer) would have three links, with a total maximum bandwidth of 19.2 gigabytes/sec. The single HyperTransport link on the Athlon 64 would be intended for connections to the system bus of a computer incorporating it, while two of three HyperTransport links on an Opteron might be used to link to other processors, making construction of a powerful multiprocessor system simple. Initial clock speeds for these processors are in the 800 MHz to 1 GHz range.
AMD has announced that systems incorporating this architecture should hit the mass market by the first quarter of 2003.
Update (January 20, 2003): A quick look at AMD's website shows that the Sledgehammer and Clawhammer codenames have been given the official brand names AMD Opteron and Athlon 64 respectively.
Sources:
Anand Lal Shimpi, "The AMD Hammer Architecture: Making Sense of it All", at .com/cpu/showdoc.html?i=1546&p=1
Anand Lal Shimpi, "AMD's Hammer in Action: The Most Impressive Demo of IDF", http://www.anandtech.com/cpu/showdoc.html?i=1591
Fred Weber, "AMD's Next Generation Microprocessor Architecture," at http://www.amd.com/us-en/Processors/ProductInformation/0,,30_118_4699,00.html
"THG Visits AMD: The First PCs With the Hammer CPU", http://www6.tomshardware.com/cpu/02q1/020227/hammer-01.html
"AMD Opteron Processor Frequently Asked Questions", http://www.amd.com/us-en/Processors/ProductInformation/0,,30_118_4699_7981%5E7987,00.html
"HyperTransport FAQ" http://www.hypertransport.org/faqs.html