Graphic Accelerator Card
Graphic accelerator cards usually come to us as add-on cards that plug into a PCI bus or AGP slot, or the circuitry is integrated into the motherboard and attached to one of these buses. A typical 2D/3D graphic accelerator card has the following major components as follows.
- Graphic accelerator chipset or co-processor
- Expansion Bus interface
- Video memory
- Firmware in Flash BIOS
- Software driver
Let’s discuss one by one.
- Graphic accelerator chipset or co-processor –
It is the brain of the video card and determines what exactly the board can and can’t do. In this, chipsets are one of the core components and better chipsets will provide you more efficient and more acceleration features. Better chipsets include extended capabilities or we can say extra functionalities like 3D acceleration or MPEG decoding.
- Expansion Bus interface –
Since many graphics operations entail copying of memory images or blocks of data from system memory to the display adapter’s on-screen memory, the expansion bus interface in terms of speed and bandwidth plays a major role in deciding the video performance. Moreover, in cheaper graphic accelerator designs featuring minimal accelerating hardware, most of the video processing tasks fall back to the PC’s processor, which makes bus performance even more important. The graphic data movement between the PC motherboard and the adapter takes place over the PC’s expansion bus. Hence it’s quite natural that a faster and wider expansion bus interface is essential for better video performance.
- Video memory –
There are two important issues with video memory of graphic accelerator cards – memory size and memory type. The video memory of traditional display adapters such as EGA, VGA, etc., was known as “frame buffer’ because core purpose of the video memory was to store frame pixel bits. In sharp contrast, the video memory chips of graphic accelerators not only stores frame pixel bits buffering removes this limitation, enabling frame rates that match the full refresh rate of the monitor.
- RAMDAC –
In low cost and earlier VGA cards, the RAMDAC is integrated into the video controller chip. But in high-performance graphic cards, the RAMDAC is separate. The Digital to Analog converter (DAC) part of the RAMDAC chip converts digital values of three primary colors into analog video signals. In this, you can say RAM on a RAMDAC is used for holding information like palette information and not for the actual image. Graphic accelerators need faster DACs to support higher screen refresh rates, which is essential for 3D graphics.
- Firmware in Flash BIOS –
All graphics accelerators require video BIOS and driver software. The video BIOS is the firmware permanently recorded on an EPROM/Flash BIOS chip. The firmware contains a minimal amount of software necessary for supporting a graphics controller to provide the desired screen environment. Also, the BIOS software interfaces the graphics accelerator hardware to a standard set of DOS functions.
- Software driver –
Drivers are actually part of the board and they play the controlling role in all graphic accelerators. In general, drivers are sophisticated chunks of code that enable graphic cards to talk and take orders from the operating system and its applications. Without the graphic card driver software, there is no way a gaming application will know how to generate the display because Windows would have no idea that the card is there.