The Looming Battle in 64 Bit Land

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Alpha’s well on the Western (and Eastern) Front

The current performance leader is the Compaq Alpha EV67 (also known as the 21264A) running at 667 MHz. The Alpha design team has recently come through several difficult years due to the sale of their Hudson Mass. wafer fab to Intel (as part of a complex settlement of DEC’s patent infringement suit against the chip giant), a subsequent acquisition of Digital Equipment Corporation (DEC) by Compaq and their own relocation from Hudson to Shrewsbury. This internal distraction, plus the complexity of the EV6 processor core design, has caused Alpha to fall out of its traditional position as clock rate leader. But the generous execution resources of the out-of-order EV6 design, coupled with the high bandwidth and low latency Tsunami chipset and mature compiler technology has allowed Alpha to retain performance leadership in SPEC2000, as well as SPECfp95, despite competition from processors with clock rates as much as 50% higher.

Within the next six months Compaq should be shipping the first 0.18 um version of the EV6 core, known as EV68 or 21264B. This device, disclosed at ISSCC 2000, is built in an 0.18 um process, but retains the die size and metal design rules from the 0.25 um EV67. This approach is for backwards compatibility with the existing 588 pin CPGA package and gets the EV68 into existing systems faster, but doesn’t realize the full benefits from the shrink. The characteristics of the EV68 process are shown below in Table 1 along with the characteristics of the Intel P856.5 process (0.25 um with 5% shrink) and the Intel P858 and IBM CMOS8S 0.18 um processes for comparison.

 Intel P856.5
(0.25 um)
Alpha EV68
hybrid 0.18/0.25
Intel P858
(0.18 um)
IBM CMOS8S
(0.18 um)

Transistor Ldrawn

0.25 um0.18 um0.18 um0.18 um

Transistor Leffective

0.20 um0.092 um0.14 um< 0.13 um

Transistor Tox

41 A36 A30 A36 A

Interconnect

AluminumAluminumAluminumCopper

M1 contacted pitch

0.61 um0.91 um0.50 um0.49 um

M2 contacted pitch

0.88 um0.91 um0.64 um0.63 um

M3 contacted pitch

0.88 umRef Plane0.64 um0.63 um

M4 contacted pitch

1.73 um2.24 um1.08 um0.63 um

M5 contacted pitch

2.43 um2.24 um1.60 um0.63 um

M6 contacted pitch

N/ARef Plane1.72 um1.26 um

M7 contacted pitch

N/A2.24 umN/A1.26 um

Table 1. Comparison of Representative 0.25 and 0.18 um Processes

Despite only partial exploitation of its 0.18 um process, the EV68 will run at clock rates exceeding 1 GHz. Future versions of the EV68 that fully exploit the 0.18 um process will achieve about 25% smaller die size, higher clock rates and lower clock normalized power consumption than the initial device. A fully 0.18 um EV68 will likely take advantage of the smaller processor core to add a moderately sized on-chip L2 cache. Beyond EV68 is an ambitious MPU design for high-end servers called the EV7 or 21364. The EV7 is based on the EV6x processor core but adds a large (1.5 Mbyte) on-chip L2 cache, on-chip memory controller/interface, and four sets of bidirectional interprocessor communication links. It is predicted to ship in systems next year. Compaq and IBM recently disclosed that IBM Microelectronics will start manufacturing Alpha processors early next year in IBM’s CMOS8S and possibly their CMOS8S2 silicon-on-insulator (SOI) process. At the 1999 Microprocessor Forum Compaq disclosed that the formidable eight issue wide, simultaneous multithreading (SMT) EV8 fourth generation Alpha processor core would be manufactured starting in 2002 in a 0.125 um, copper, low k dielectric SOI compatible process. Those specifications strongly suggest that the manufacturing relationship with IBM will be even more intimate in the future.


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