One of the more interesting features of the Radeon 256 is its support for something ATI likes to call HyperZ technology.
When talking about conserving memory bandwidth, a major hog is the Z-Buffer, which determines how “deep” objects on the screen are supposed to be. Especially when dealing with a 32-bit Z-Buffer, which requires twice the storage space as a 16-bit Z-Buffer, you lose quite a bit of memory bandwidth because of the Z-Buffer.
ATI’s HyperZ technology borrows its theory from tile based rendering architecture (such as that found on the PowerVR2), which basically renders any given scene in tiles instead of on a per polygon basis, which allows objects that aren’t going to be visible to the viewer (because they are covered up by other objects) to be skipped during the rendering process.
Now since the Radeon 256 doesn’t boast a tile based rendering architecture, it cannot render a scene in this manner; this is where HyperZ comes in. HyperZ enables various forms of compression of the data going to the Z-buffer and performs an early culling of polygons so that objects that aren’t visible to the viewer aren’t rendered.
According to ATI, when enabled, HyperZ technology can boost the effective memory bandwidth by 20% and increase the fill rate of the Radeon 256 to 1.5 gigatexels per second, up from the 1.2 gigatexels per second fill rate that the Radeon 256 would otherwise have.
As scenes become more complex (which ATI is counting on, hence their support for a hardware T&L engine – Charisma Engine), the benefits of the HyperZ technology’s improvements on reads/writes to the Z-buffer will become amplified.