HP unveiled its most powerful server yet last week, called Superdome, while IBM has plans to launch a server clustering solution called Blue Hammer.
HP's 64-bit PA-Risc chip Superdome, which will sell for more than $1m will go head-to-head with Sun's flagship Enterprise 10000.
Meanwhile, HP's plan to acquire the consulting arm of Andersen is being seen as an attempt to sell services alongside hardware installations.
HP is also pushing into new billing models with Superdome, where it will sell boxes with extra processors that can be "switched on" and billed for accordingly.
Ultimately, HP aims to charge in the manner of a utility - billing only for processing power used.
IBM's Blue Hammer clusters several RS/6000 S80 AIX servers into a single entity using Parallel System Support Programs software originally devised for Deep Blue supercomputers.
The PSSP software allows clustering of up to 16 S80 servers, with management available from a single point. A base configuration of two six-way clustered S80s starts at $705,000.
Industry observers regard the threat from HP and IBM as the least of Sun's worries, given the company's delay in introducing the Ultrasparc III chip for its Serengeti servers, due at the end of September.
Sun, the Unix server market leader since 1998, has seen tremendous growth based on the take-up of its products by Internet-related businesses.
Servers square up
ibm blue hammer
sun enterprise 10000