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Aero is the base set of requirements for Avalon, and will require DirectX 9 (with Pixel Shader 2.0 support), 32MB VRAM minimum, and AGP 4X for a GPU or UMA. If a system does not reach this minimum, it will not get the "Designed for Windows" logo. Aero Glass will offer a richer experience. It will require DirectX 9 (with Pixel Shader 2.0 support), 64MB VRAM minimum (128MB recommended), and AGP 4X for a GPU. Microsoft is still deciding whether to allow a dual-channel UMA implementation to qualify for the logo. The company will offer a "classic" level, though technically not an Avalon tier, for systems that don't meet minimum requirements. This will allow Longhorn to run on less powerful PCs, but with an interface more akin to the Windows 2000 look and feel.

DirectX 9? Pixel Shader 2.0? The cards supporting this technology have only just been announced, really; ATI's brand new (and announced today) R420-based X800 and NVidia's NV40-based GeForce 6800 represent both the entry level requirements for Longhorn's release (or at least a scaled up version of those entry level requirements - this is the generation, if not the model, of the entry level) and the cutting edge of video technology.

Fundamentally, this is a similar move to what Apple has done with Quartz Extreme: it's a high-end visual composition system, fundamentally, featuring the occasional 3d effect thrown in purely because you can, really.

A standard 2D composition system draws windows as rectangles into screen bitmaps, and either composes them together or does it in-situ via direct framebuffer access. There's no 3d; even though things lay "on top of" each other, that's accomplished by drawing one square box over another. Because the windowing system can predict what will overlay what, it can make some predictions as to what will be visible, and ensure that it limits what is called "overdraw" - or the drawing of the same pixel more than once if it's obscured by another window.

Quartz Extreme changed that: Apple implemented its OpenGL subsystem so that it was capable of using 3D graphics hardware, the same hardware used by 3D games, to do that work. Instead of trying to compose something that behaved like 3D layers out of a set of bitmaps, it turned each window into a texture, and in the same way that a game engine puts a skin on a 3D model, the graphics composition engine puts a skin on a 2d 'square' in 3D space. The effect is that while it looks flat, all of the actual work of composing that screen is performed on the graphics card. Applications only ever need to update themselves; the graphics card is responsible for everything from moving windows to one window obscuring another; it's the reason why Mac menus are semi-transparent, and why alert boxes pop up three-dimensionally out of the top of window menus.

3D graphics effects enable a revolution in the way user interfaces are presented; things that were inefficient before are suddenly not only acceptable, but easy to accomplish. The primary enablers are three effects:

• Large bitmap areas can be moved for free.
  Making one part of a window slide out of another, such as a drawer or an alert box (a "sheet", on macs, are 'attached' to their originating window), is essentially free; they're just manipulations of the rectangular 'body' that the texture 'window' is painted on. This means that window effects - where one window moves smoothly while another is attached to it, or is a surrogate of it - is free.


• Transparency.
  The single most obvious difference, and one of the most powerful. This touches everything - menus can be made slightly transparent, so as not to be distracting, but to allow the user to get a view of what the menu is obscuring.
  Those alert boxes, or sheets, are slightly transparent, too - so that, again, the presence of a dialog isn't blocking out 100% of your view of the window behind it; how often have you had a dialog where some of the information you need to enter into it is blocked in the window sitting behind it... And drop-shadows, made popular and fast in Quartz, will be coming everywhere. They're essentially free - they cost nothing to render under a 3D compositor, and create a useful visual separation between layers.


• Use of the 3D nature of the windowing environment.
  Apple, once again, has been at the forefront of this development: 10.1 brought 'free' dock minimization - the ability to take a window and shrink it out of the way, not into a title bar, but into a miniaturized version of the window; movies playing back in that window remain animated in the dock; changes to the window are immediately visible in the shrunken version of the application.10.3 brought Exposé - three features really, which are the ability to Shrink all windows so that they all fit on screen and let the user choose which window he wants to see next from the mosaic of windows, 'fog out' all windows except the active application, and do the same effect, or a fast desktop view which slides all windows out to the edges of the screen, so that you can grab something from off of the desktop. These features use the inherent 3D paradigm given to them by a 3D rendering engine, and try to find new ways of letting the user navigate through his or her workspace.10.3 also brought XP-like multiuser functionality; the screen renders on to the surface of a cube, which is pulled back and rotated to another face; that other face is another screen.

Similar changes are on the road ahead for Longhorn users; like their Mac brethren, they will get a 3D graphics compositor, dubbed Avalon, capable of allowing the user interface developers to do new things. The window borders in Aero Glass around inactive windows are semi-transparent; you can see through them to the contents behind.

Mind you, all of Microsoft's demos died horribly during the performance at the developer conference; while pretty, they are a long way off from being a part of the everyday experience of windows users. To boot, full DX9 compatibility is needed, including a minimum of 32MB of graphics memory for the 'basic' Aero, and 64MB for the full-fledged Aero Glass look. And Glass really wants 128MB - which is more memory than many people's PCs have in main memory, to be honest, an unfortunate truth.

Which is where all the new graphics cards come in: With their full DX9 compatibility, support for Pixel Shader 2.0, and minimum memory levels of 64-128MB, these cards, which today cost over $400, will be the minimum requirements for Longhorn on release. The war on graphics chipsets have become so predictable, and such a high commodity item, that Microsoft can bet on their widespread availability in consumer hardware at a low enough price point to force the upgrade of millions of computer systems (and realistically, it will be forced - this is the nature of 3D compositing, there's no halfway house).

So things are looking up for gaming. Microsoft's just gone and blown the doors open on the market - and so the winner of this round of graphics cards, NVidia's 6400 vs. ATI's X800, stands to win not just the adoration of gamers, but the widespread adoption across the millions of new and to-be-upgraded PCs which will need these graphics capabilities not to play games, but to write simple documents, send e-mail, or even just browse the web.

The cards themselves couldn't be more different.

NVidia's radical design rivals that of any CPU design - a highly flexible, highly programmable system of interlocking components capable of driving a flexible and dynamic video pipeline. In other words, the game and the drivers shape the capabilities of the hardware, and there's a lot of room to manoeuvre, not just between games, but within the rendering of a single frame of animation. ATI's is a more traditional approach - carefully designed pipelines meeting specific requirements and goals, with a far smaller and lightweight design, and a lot less power and thermal requirements.

Both promise, and can likely offer, the kinds of effects on the small screen that we've come to expect from expensive films on the big screen; realism, or non-realism, at the artists' commands, to rival those of the theatrical experiences. Soft edges, realistic shadows, motion blur, and capabilities to emulate the behavior of the human eye's reaction to light and dark conditions are just the tip of the iceberg. It's materials technology that really differentiates the capabilities of the new set of GPUs from the old; the ability to run long, complex programs to do lighting and surface creation, instead of relying on more and more polygons, and more and more textures. Things will look rounder and less edgy; subsurface scattering, a natural characteristic of all non-metallic surfaces, allow light to not just bounce off the surface, but to bounce off of the contents; a glass of milk isn't just "white" - light reflects off of and through that milk, giving it a strange visual quality that a glass of white paint just doesn't have. Today, that glass of milk looks like white paint; tomorrow, it's going to look a lot more like milk. Pottery, too - with the shiny coat of glaze translucent over the pigments beneath it, become easy to create, as do stones like translucent marble and glass effects like frosting and warping.

NVidia went down a road that gives them general purpose flexibility; ATI has gone down the more traditional road, and bundled in a bunch of new capabilities to their existing, winning hardware design - an evolution, in opposition to NVidia's revolution. ATI has an early lead on performance, though - furhter evolution in NVidia's drivers might change that.

These graphics cards will decompress video for you - decoding DIVX, WMV9, and VCDs impressively (ATI being the more impressive of them - but that has always been true, and given the last few years, I'd guess always will) without the use of your main CPU. This matters most when you like watching full-screen video, of course. And in tests performed by Tom's Hardware the ATI fared incredibly well: beating the NVidia in many tests with what is undoubtedly a much less expensive design, with both cards being early releases of what will eventually be final versions of drivers once the cards have settled into the market.

ATI once again rules image quality, though - and its stellar performance may place it in the winner's circle with the flood of new buyers destined for upgrades to their system in the year ahead to prepare for what will undoubtedly be an unforgettable launch of Microsoft's biggest endeavour yet: a reinvention of Windows so extreme that users will be compelled to upgrade in droves, in a way only ever seen twice before: the long-ago upgrade from Windows 3.1 to Windows 95, and the very recent move by Apple from Mac OS 9 to Mac OS X.