ATI Mobility Radeon Preview

HyperZ Revisited

ATI has also included HyperZ technology in the Mobility Radeon, meaning that this mobile processor can also benefit from the memory bandwidth optimizations that come with the technology. You may recall that HyperZ technology, made up of Hierarchical Z, Z-Compression, and Fast Z-Clear, was able to bring new performance to the 3D graphics market. Luckily, the Mobility Radeon is able to bring this technology to the mobile platform, especially considering what kind of memory bandwidth limitations will surely exist.

Why, you may ask, will memory bandwidth be even more important in a laptop? The reason is a result of ATI's choice in memory bus widths. The Mobility Radeon core is able to support two different memory bus widths: 32-bit and 64-bit wide configurations. Now compare this to the 128-bit memory bus that is currently limiting us in desktop 3D and you see where the problem comes in.

The most likely configurations for the Mobility Radeon's memory subsystem are 32-bit DDR and 64-bit SDR solutions. Although a 64-bit DDR solution is possible, it is unlikely that many manufacturers will put the extra money into producing such a solution, as it is much cheaper to use the 32-bit solution with DDR memory than it is to use either a 64-bit SDR or a 64-bit DDR solution.

In either popular configuration, both 32-bit DDR and 64-bit DDR, the memory system is left with very little memory bandwidth. ATI suggested that possible memory clock speeds were up to 166 MHz or 183 MHz. Both ways leave the system severely crippled: with only 1.3GB/s (166 MHz) or 1.5GB/s (183 MHz), both solutions fall short of the 5.8GB/s that current DDR desktop cards posses.

It is for this reason that HyperZ technology is going to play a crucial role for the Mobility Radeon. By essentially decreasing the amount of data that must travel over the memory bus, the Mobility Radeon will not be as memory bandwidth crippled as other solutions out there, including NVIDIA's GeForce2 Go. However, the GeForce2 Go does feature support for a 128-bit bus, meaning that theoretically the memory bandwidth could be brought up to the level we see in current desktop solutions. The sad truth of the matter is that it is extremely unlikely that we will see any manufacturers take advantage of this high end memory bus support, as the amount of traces required for it would be very costly and take up quite some space.

On the subject of clock speeds, ATI mentioned to us that the Mobility Radeon is able to operate at clock speeds from 166 MHz or 183 MHz all the way down to 66 MHz. More on that low number in a minute, but it is clear that the Mobility Radeon is able to clock right up there with its desktop counterpart.