This article originally appeared on
CPU Planet.
Nobody denies that Intel's
0.13-micron-architecture Pentium 4 "Northwood" is a powerful processor, but it's
only the second strongest chip in many PC gamers' desktops. The GeForce 6800
Ultra graphics processing unit (GPU) that Nvidia Corp. introduced last week has
over 220 million transistors -- as many as four Northwoods or two of AMD's
Athlon 64s, without using millions for on-chip cache as the PC processors do. If
you think technical jargon about clock speeds and memory interfaces is only for
CPUs, it's time you got up to speed on another silicon arena, where the warring
superpowers are Nvidia and ATI Technologies instead of Intel and AMD. Let's take
an introductory look at the engines that power today's games' and animated
films' increasingly realistic 3D worlds.
Nvidia coined the acronym GPU -- and
defined it as a single-chip processor with integrated transform, lighting,
triangle setup/clipping, and rendering engines, capable of producing at least 10
million polygons per second -- when introducing its GeForce 256 in August 1999.
Archrival ATI tries to avoid the term, referring to "visual processing units"
(or, for its motherboard chipsets, "integrated graphics processors"), but the
GPU tag has become popular enough for our purposes.
Whether in a game player's PC or a
scientific engineer's workstation, the GPU is designed to take a load off the
system processor by handling the majority of 3D rendering and setup duties.
Ever-more-complex transform and lighting (T&L) engines and vertex and pixel
processors have promoted GPUs' growth in size and complexity, but most consist
of the same basic components, seen below in ATI's block diagram of its R350 (Radeon
9700 Pro) core.
Some old-school parts of the chip
include the 2D engine for productivity applications and image editing -- once
the main performance consideration, now considerably overshadowed by the 3D
circuitry -- and interfaces that pass data in and out of the GPU, whether the
AGP bus (soon to be pushed aside by PCI Express) or various interfaces for
various types of monitors such as CRTs and LCDs. (If you run into the term
RAMDAC, it's short for Random Access Memory Digital-to-Analog Converter and
converts digital image data to analog for a CRT's red, green, and blue electron
guns; a higher RAMDAC clock offers faster screen-refresh rates.)
Moving further into the GPU brings us
to today's main attractions, the 3D-specific components. These may differ in
terms of naming conventions and architectural design, but remain pretty
consistent in terms of function, and include various setup engines, memory
compression algorithms (HyperZ III in ATI's chart), an antialiasing unit, memory
interface, and 3D rendering engine.
