The Battle in 64 bit Land, 2003 and Beyond

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Alpha: Haunting Rivals from Beyond the Grave

Despite being kept on minimum life support and locked in a dark crawl space, HP’s unwanted bastard stepchild Alpha continues to confound friends and foes alike. The last major revamp of the venerable EV68, to 1250 MHz, has proven surprisingly formidable for this small, 15 million transistor device. The ability of the latest EV68-based hardware to hang tough with expensive MCM packaged POWER4 systems bulging with custom silicon L3 cache is a stark testament to the architectural design and silicon engineering that went into the EV6x processor core so many years ago. This core will live on for years to come in the form of the newly introduced EV7, effectively a single chip supercomputer compute node.

Due to the decision to accept a relatively slow, low bandwidth on-chip L2 cache rather than modify the EV6 core (which was optimized around off-chip cache) the EV7 is not appreciable faster than the EV68 on single threaded applications or in uniprocessor systems. But EV7’s performance within large scale systems will likely be beyond peer for years to come. A comparison of a prototype 16 processor EV7 system to a 4 processor ES45 system indicates the EV7 gear has twice the per CPU memory bandwidth and much better inter-processor communication performance (MPI) than a 4 processor, cross-bar based ES45 system [2]. The results are summarized in table 1.

<b>Table 1: Comparison of EV68 and Prototype EV7 Alpha Systems</b>
&nbsp;

ES45

4 x EV68/1000

Prototype

16 x EV7/1200

Memory, local, read bandwidth (GB/s)

2.27

4.58

Memory, remote, read bandwidth (GB/s)

N/A

3.60

MPI, unidirectional, latency (&#109; s)

4.9

1.7

MPI, unidirectional, bandwidth (MB/s)

792

1080

MPI, unidirectional, latency (&#109; s)

8.9

2.2

MPI, unidirectional, bandwidth (MB/s)

379

485

If the EV7 wasn’t bad enough for competitors in the high performance computing (HPC) market who wish Alpha would just quietly accept its death, HP has recently confirmed that it will keep Compaq’s commitment to bring the 0.13 &#109;m shrink of the EV7, the EV79, to market in about a year. No doubt airtight contracts with various government labs inherited from Compaq figured prominently in this decision. The EV79 will incorporate a larger L2 cache than EV7 (probably 3 MB) as well as support faster (PC1066) memory.

Large scale EV7x systems will be relatively inexpensive to build (look ma, no chipset!) but expect HP to charge top dollar regardless. Since the acquisition of Compaq, HP’s official policy has been to direct all new customers to IA64 hardware and limit sales of Alpha systems to the remaining customer base. But with PA-RISC long toothless for technical computing and a number of vendors like SGI offering huge Itanium 2 based systems optimized for HPC, sheer pragmatism will likely force HP to sell EV7x gear to anyone with approved credit. Obscenely high prices will ensure the Alpha tail doesn’t wag the IA64 dog.


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