Video Hardware, Part 2 - Super VGA
(Page 10 of 10 )
When IBM's XGA and 8514/A video cards were introduced, competing manufacturers chose not to attempt to clone these incremental improvements on their VGA products. Instead, they began producing lower-cost adapters that offered even higher resolutions. These video cards fall into a category loosely known as Super VGA (SVGA).
SVGA provides capabilities that surpass those offered by the VGA adapter. Unlike the display adapters discussed so far, SVGA refers not to an adapter that meets a particular specification, but to a group of adapters that have different capabilities.
For example, one card might offer several resolutions (such as 800x600 and 1024x768) that are greater than those achieved with a regular VGA, whereas another card might offer the same or even greater resolutions but also provide more color choices at each resolution. These cards have different capabilities; nonetheless, both are classified as SVGA.
The SVGA cards look much like their VGA counterparts. They have the same connectors, but because the technical specifications from different SVGA vendors vary tremendously, it is impossible to provide a definitive technical overview in this book. The connector is shown in Figure 15.10; the pinouts are shown in Table 15.7.
Figure 15.10 VGA connector used for SVGA and other VGA-based standards.
Table 15.7 Standard 15-Pin VGA Connector Pinout Pin # | Function | Direction |
1 | Red video | Out |
2 | Green video | Out |
3 | Blue video | Out |
4 | Monitor ID 2 | In |
5 | TTL Ground (monitor self-test) | – |
6 | Red analog ground | – |
7 | Green analog ground | – |
8 | Blue analog ground | – |
9 | Key (plugged hole) | – |
10 | Synch Ground | – |
11 | Monitor ID 0 | In |
12 | Monitor ID 1 | In |
13 | Horizontal Synch | Out |
14 | Vertical Synch | Out |
15 | Monitor ID 3 | In |
On the VGA cable connector that plugs into your video adapter, pin 9 is often pinless. Pin 5 is used only for testing purposes, and pin 15 is rarely used; these are often pinless as well. To identify the type of monitor connected to the system, some manufacturers use the presence or absence of the monitor ID pins in various combinations.
VESA SVGA Standards The Video Electronics Standards Association includes members from various companies associated with PC and computer video products. In October 1989, VESA recognized that programming applications to support the many SVGA cards on the market was virtually impossible and proposed a standard for a uniform programmer's interface for SVGA cards; it is known as the VESA BIOS extension (VBE). VBE support might be provided through a memory-resident driver (used by older cards) or through additional code added to the VGA BIOS chip itself (the more common solution). The benefit of the VESA BIOS extension is that a programmer needs to worry about only one routine or driver to support SVGA. Various cards from various manufacturers are accessible through the common VESA interface. Today, VBE support is a concern primarily for real-mode DOS applications, usually older games, and for non-Microsoft operating systems that need to access higher resolutions and color depths. VBE supports resolutions up to 1280x1024 and color depths up to 24-bit (16.8 million colors), depending on the mode selected and the memory on the video card. VESA compliance is of virtually no consequence to Windows versions 95 and up. These operating systems use custom video drivers for their graphics cards.
Note -For a listing of VESA BIOS modes by resolution, color depth, and scan frequency, see "VESA SVGA Standards" in the Technical Reference portion of the disc accompanying this book.
 | This chapter is from Upgrading and Repairing PCs, 16th edition,by Scott Mueller. (Que Books, 2004, ISBN: 0789731738). Check it out at your favorite bookstore today. Buy this book now! |
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