VGPU: Visual Graphics Processing Unit
A graphics processing unit or GPU (also occasionally called visual processing
unit or VPU) is a dedicated graphics rendering device for a personal computer,
workstation, or game console. Modern GPUs are very efficient at manipulating and
displaying computer graphics, and their highly parallel structure makes them
more effective than typical CPUs for a range of complex algorithms. A GPU can
sit on top of a video card, or it can be integrated directly into the
motherboard in more than 90% of desktop and notebook computers (although
integrated GPUs are usually far less powerful than their add-in counterparts).
A GPU implements a number of graphics primitive operations in a way that makes
running them much faster than drawing directly to the screen with the host CPU.
The most common operations for early 2D computer graphics include the BitBLT
operation (combines several bitmap patterns using a RasterOp), usually in
special hardware called a "blitter", and operations for drawing rectangles,
triangles, circles, and arcs. Modern GPUs also have support for 3D computer
graphics, and typically include digital video-related functions.
History
Early 1980s
Modern GPUs are descended from the monolithic graphic chips of the early 1980s
and 1990s. These chips had limited BitBLT support in the form of sprites (if
they had BitBLT support at all), and usually had no shape-drawing support. Some
GPUs could run several operations in a display list, and could use DMA to reduce
the load on the host processor; an early example was the ANTIC co-processor used
in the Atari 800 and Atari 5200. In the late 1980s and early 1990s, high-speed,
general-purpose microprocessors became popular for implementing high-end GPUs.
Several high-end graphics boards for PCs and computer workstations used TI's
TMS340 series (a 32-bit CPU optimized for graphics applications, with a frame
buffer controller on-chip) to implement fast drawing functions; these were
especially popular for CAD applications. Also, many laser printers from Apple
shipped with a PostScript raster image processor (a special case of a GPU)
running on a Motorola 68000-series CPU, or a faster RISC CPU like the AMD 29000
or Intel i960. A few very specialised applications used digital signal
processors for 3D support, such as Atari Games' Hard Drivin' and Race Drivin'
games.
As chip process technology improved, it eventually became possible to move
drawing and BitBLT functions onto the same board (and, eventually, into the same
chip) as a regular frame buffer controller such as VGA. These cut-down "2D
accelerators" were not as flexible as microprocessor-based GPUs, but were much
easier to make and sell.
1980s
The Commodore Amiga was the first mass-market computer to include a blitter in
its video hardware,and IBM's 8514 graphics system was one of the first PC video
cards to implement 2D primitives in hardware.
The Amiga was unique, for the time, in that it featured what would now be
recognized as a full graphics accelerator, offloading practically all video
generation functions to hardware, including line drawing, area fill, block image
transfer, and a graphics coprocessor with its own (though primitive) instruction
set. Prior (and quite some time after on most systems) a general purpose CPU had
to handle every aspect of drawing the display.
1990s
By the early 1990s, the rise of Microsoft Windows sparked a surge of interest in
high-speed, high-resolution 2D bitmapped graphics (which had previously been the
domain of Unix workstations and the Apple Macintosh). For the PC market, the
dominance of Windows meant PC graphics vendors could now focus development
effort on a single programming interface, Graphics Device Interface (GDI).
In 1991, S3 Graphics introduced the first single-chip 2D accelerator, the S3
86C911 (which its designers named after the Porsche 911 as an indication of the
speed increase it promised). The 86C911 spawned a host of imitators: by 1995,
all major PC graphics chip makers had added 2D acceleration support to their
chips. By this time, fixed-function Windows accelerators had surpassed expensive
general-purpose graphics coprocessors in Windows performance, and these
coprocessors faded away from the PC market.
Throughout the 1990s, 2D GUI acceleration continued to evolve. As manufacturing
capabilities improved, so did the level of integration of graphics chips. Video
acceleration became popular as standards such as VCD and DVD arrived, and the
Internet grew in popularity and speed. Additional application programming
interfaces (APIs) arrived for a variety of tasks, such as Microsoft's WinG
graphics library for Windows 3.x, and their later DirectDraw interface for
hardware acceleration of 2D games within Windows 95 and later.
In the early and mid-1990s, CPU-assisted real-time 3D graphics were becoming
increasingly common in computer and console games, which lead to an increasing
public demand for hardware-accelerated 3D graphics. Early examples of
mass-marketed 3D graphics hardware can be found in fifth generation video game
consoles such as PlayStation and Nintendo 64. In the PC world, notable failed
first-tries for low-cost 3D graphics chips were the S3 ViRGE, ATI Rage, and
Matrox Mystique. These chips were essentially previous-generation 2D
accelerators with 3D features bolted on. Many were even pin-compatible with the
earlier-generation chips for ease of implementation and minimal cost. Initially,
performance 3D graphics were possible only with separate add-on boards dedicated
to accelerating 3D functions (and lacking 2D GUI acceleration entirely) such as
the 3dfx Voodoo. However, as manufacturing technology again progressed, video,
2D GUI acceleration, and 3D functionality were all integrated into one chip.
Rendition's Verite chipsets were the first to do this well enough to be worthy
of note.
As DirectX advanced steadily from a rudimentary (and perhaps tedious) API for
game programming to become one of the leading 3D graphics programming
interfaces, 3D accelerators evolved seemingly exponentially as years passed.
Direct3D 5.0 was the first version of the burgeoning API to really dominate the
gaming market and stomp out many of the proprietary interfaces. Direct3D 7.0
introduced support for hardware-accelerated transform and lighting (T&L). 3D
accelerators moved beyond of being just simple rasterizers to add another
significant hardware stage to the 3D rendering pipeline. The NVIDIA GeForce 256
(also known as NV10) was the first card on the market with this capability.
Hardware transform and lighting set the precedent for later pixel shader and
vertex shader units which were far more flexible and programmable.
2000 to present
With the advent of the DirectX 8.0 API and similar functionality in OpenGL, GPUs
added programmable shading to their capabilities. Each pixel could now be
processed by a short program that could include additional image textures as
inputs, and each geometric vertex could likewise be processed by a short program
before it was projected onto the screen. NVIDIA was first to produce a chip
capable of programmable shading, the GeForce 3 (core named NV20). By October
2002, with the introduction of the ATI Radeon 9700 (also known as R300), the
world's first Direct3D 9.0 accelerator, pixel and vertex shaders could implement
looping and lengthy floating point math, and in general were quickly becoming as
flexible as CPUs, and orders of magnitude faster for image-array operations.
Pixel shading is often used for things like Bump mapping which adds texture, to
either make an object look shiny, dull, rough, or even round or extruded.
Today, parallel GPUs have begun making computational inroads against the CPU,
and a subfield of research, dubbed GPGPU for General Purpose Computing on GPU
has found its way into fields as diverse as oil exploration, scientific image
processing, and even stock options pricing determination. There is increased
pressure on GPU manufacturers from "GPGPU users" to improve hardware design,
usually focusing on adding more flexibility to the programming model.
GPU companies
There have been many companies producing GPUs over the years, under numerous
brand names. The current dominators of the market are ATI (manufacturers of the
ATI Radeon graphics chip line) and NVIDIA (manufacturers of the NVIDIA Geforce
graphics chip line.) Intel also produce GPUs that are built into their
motherboards, such as the 915 and 945. These chips are often less than optimum
for playing 3D games, and fixes often have to be applied. Although most games
will play on the Intel chips (except for the few that are specifically coded not
to run on it), frame rates will often become unplayable, even at the lowest
settings. The 965 chipset is marginally faster, and finally includes hardware
T&L, but the integrated nature of the chipset still gives a large performance
hit.
Computational functions
Modern GPUs use most of their transistors to do calculations related to 3D
computer graphics. They were initially used to accelerate the memory-intensive
work of texture mapping and rendering polygons, later adding units to accelerate
geometric calculations such as translating vertices into different coordinate
systems. Recent developments in GPUs include support for programmable shaders
which can manipulate vertices and textures with many of the same operations
supported by CPUs, oversampling and interpolation techniques to reduce aliasing,
and very high-precision color spaces. Because most of these computations involve
matrix and vector operations, engineers and scientists have increasingly studied
the use of GPUs for non-graphical calculations.
In addition to the 3D hardware, today's GPUs include basic 2D acceleration and
frame buffer capabilities (usually with a VGA compatibility mode). In addition,
most GPUs made since 1995 support the YUV color space and hardware overlays
(important for digital video playback), and many GPUs made since 2000 support
MPEG primitives such as motion compensation and iDCT. Recent graphics cards even
decode high-definition video on the card, taking some load off the central
processing unit.
GPU forms
Dedicated graphics cards
The most powerful class of GPUs typically interface with the motherboard by
means of an expansion slot such as PCI Express (PCIE) or Accelerated Graphics
Port (AGP) and can usually be replaced or upgraded with relative ease, assuming
the motherboard is capable of supporting the upgrade. However, a dedicated GPU
is not necessarily removable, nor does it necessarily interface with the
motherboard in a standard fashion. The term "dedicated" refers to the fact that
dedicated graphics cards have RAM that is dedicated to the card's use, not to
the fact that most dedicated GPUs are removable. Dedicated GPUs for portable
computers are most commonly interfaced through a non-standard and often
proprietary slot due to size and weight constraints. Such ports may still be
considered AGP or PCI Express, even if they are not physically interchangeable
with their counterparts.
Multiple cards can draw together a single image, so that the number of pixels
can be doubled and antialiasing can be set to higher quality. If the screen is
parted into a left and right, each card can cache the textures and geometry from
their side.
Integrated graphics solutions
Integrated graphics solutions, or shared graphics solutions are graphics
processors that utilize a portion of a computer's system RAM rather than
dedicated graphics memory. Such solutions are typically far less expensive to
implement in comparison to dedicated graphics solutions, but at a trade-off of
being far less capable and are generally considered unfit to play modern games
as well as run graphically intensive programs such as Adobe Flash. (Examples of
such IGPs would be offerings from SiS and VIA circa 2004.) However, todays
integrated solutions such as the Intel's GMA X3000 (Intel G965), AMD's Radeon
X1250 (AMD 690G) and NVIDIA's GeForce 7050 PV (NVIDIA nForce 630a) are more than
capable of handling 2D graphics from Adobe Flash or low stress 3D graphics. Of
course the aforementioned GPUs still struggle with high-end video games. Modern
desktop motherboards often include an integrated graphics solution and have
expansion slots available to add a dedicated graphics card later.
As a GPU is extremely memory intensive, an integrated solution finds itself
competing for the already slow system RAM with the CPU as it has no dedicated
video memory. System RAM may be 2 GB/s to 12.8 GB/s, yet dedicated GPUs enjoy
between 10 GB/s and 160 GB/s of bandwidth depending on the model. Older
integrated graphics chipsets lacked hardware transform and lighting, but newer
ones include it.
Hybrid solutions
This newer class of GPUs competes with integrated graphics in the low-end PC and
notebook markets. The most common implementations of this are ATi's HyperMemory
and NVIDIA's TurboCache. Hybrid graphics cards are somewhat more expensive than
integrated graphics, but much less expensive than dedicated graphics cards.
These also share memory with the system memory, but have a smaller amount of
memory on-board than discrete graphics cards do to make up for the high latency
of the system RAM. Technologies within PCI Express can make this possible. While
these solutions are sometimes advertised as having as much as 512MB of RAM, this
refers to how much can be shared with the system memory.
Stream processing/GPGPU
GPGPU and Stream processing
A new concept application for GPUs is that of stream processing and the general
purpose graphics processing unit. This concept turns the massive floating-point
computational power of a modern graphics accelerator's shader pipeline into
general-purpose computing power, as opposed to being dedicated solely to
graphical operations. In certain applications requiring massive vector
operations, this can yield several orders of magnitude higher performance than a
conventional CPU. The two largest discrete GPU designers, ATI and NVIDIA, are
beginning to pursue this new market with an array of applications. ATI has
teamed with Stanford University to create a GPU-based client for its
Folding@Home distributed computing project that in certain circumstances yields
results forty times faster than the conventional CPUs traditionally used in such
applications
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