For those who aren't familiar with these handy devices, CAMs can search their entire contents in a single cycle for a particular piece of data, at speeds of up to 100 million searches a second. This function is particularly prized in networking systems that must seek a particular entry in a route table or other database.

Using standard memory, a processor might require as many as a dozen memory accesses to perform such a search. In systems that operate at up to 1 Gbit/second, that overhead can be tolerated.

But at OC-48 (2.4 Gbits/s), CAMs are often used to reduce the number of accesses required. And at 10 Gbits/s, almost all network processors (NPUs) require CAMs when operating at full speed. As networking shifts to those higher line rates, demand for CAMs will grow.

Foreseeing that increase in demand, several of the large specialty-memory vendors have jumped into the CAM market either through acquisition or internal development. When the sharks start eating the guppies, it's a sign that a market is getting serious.

IDT was the first to enter, parlaying a key design win at Cisco into the number-one position in the 2001 CAM market. Former market leader Lara Networks was promptly acquired by Cypress Semiconductor. Earlier this year, Micron purchased the CAM assets of Music Semiconductor, and ISSI acquired CAM startup Purple Ray.

These and other CAM vendors are adjusting their product strategies to accommodate the shift from ASIC- to NPU-based designs. Most CAMs today use proprietary interfaces that are simple for ASIC designers to implement. But those parts often require glue logic when connected to standard NPUs.

Vendors such as IDT and startup NetLogic are deploying new CAMs that connect gluelessly to popular NPUs from Intel, AMCC and others. That task will be simplified when both NPUs and CAMs adopt the Look-Aside Interface, which is nearing approval by the Network Processing Forum.

The reason that CAMs have yet to fulfill their promise is that, down inside, no one really likes them. CAMs are power-hungry and expensive. In some designs, the CAMs cost more than the NPU. But in high-end networking systems, there are few remaining options.

Maybe this time, CAMs will win.

LInley Gwennap is Founder and Principal Analyst of the Linley Group (www.linleygroup.com).