The End is Near

VL-Bus Continued

The high speed VL-Bus was well suited to the new bandwidth hungry VGA accelerators, opening up new worlds of resolution and color depth. Providing for some of the most realistic looking computer graphics to date. However, several limitations existed for the VL-Bus, more notably there were electrical issues that restricted the full operating speed of the bus. No buffers were used on the VL-Bus, which means that VL-Bus cards were connected directly to the CPU. This put a high electrical load on the system CPU, causing a restriction in overall performance. This electrical dependence on the system processor limited the amount of VL-Bus cards that could be installed into a system. Most commonly only 2 or 3 slots could be installed into a VL-Bus system. It was general opinion that it was not a good idea to use more than 2 VL-Bus devices in a system at once.

VL-Bus used an extension slot that connected cards directly to the CPU

VL-Bus used no buffers or additional circuitry at all. It simply tapped directly into the processor bus. As a result, it was a very cheap bus to implement, which is why it appeared on 486 systems practically overnight. However, the 486 processor was not designed to have such a large electrical loads placed upon it. Because of this, the VL-Bus tended to be rather unstable, and fell out of disfavor quickly when Intel released the PCI local bus specification.

Coming up

This wraps up the second section of "How it Works: Display Adapters", which focused mainly on the history and the advancement of the generations of video technology. Look for Part III to come soon, when we examine the newer local buses, and how they helped video technology.

We will take a look at exactly how 3D graphics are created, and some of the interesting challenges that face those who create them. And we will discuss many of the different technologies associated with today's 3D graphics and look at where it is going in the future.

Also in part III, we'll take a look at how the video card talks to the computer, and the important role that the driver software plays in this interaction. We'll breakdown the different API's, and find out exactly what they do, and why they are here.