> I have a Cirrus GD-5428 based VLB video card, and there's an >undocumented jumper that apparently serves to enable or disable IRQ number 9 >(being disabled the default setting). My question is: what is the difference >between enabling it or not? Will I gain some extra feature enabling it? (I've >tried it, but nothing seems to change). Any idea? > This is one of the great mysteries of the world, equivalent to why there is no channel 1 on your regular TV. Long, long ago there was once a company called IBM, which, I've been told, stood for Idiots Both Me. They had a lot of technology but little understanding of marketing. One of their favorite tricks was to completely disregard the de facto standards and make their own, often conflicting, ones. For example, the regular coffee in their cafeteria is in orange pots and the decaffeinated in the plain pots because orange is the international warning color (the Black Box recorder of air planes is painted orange), and their marketing people felt this would warn people the coffee contained caffeine. Internal dissent was frowned on and those that did were replaced; those that said yes to the marketing people promoted. If one division came up with a better mousetrap, the mousetrap division would make them put in an escape path feature for the mouse to insure the divisions would not be in direct competition. To make a long story short, IBM decided to form a new Video standard called the VGA, short for God Awful Video. (IBM also employed dyslectic writers/proofreaders to help its PC--Political Correct--image.) But the GAV developers could not agree if the VGA card should be able to generate an interrupt when the vertical refresh trace started. Such an interrupt was standard on the EGA, (Extra Awful Graphic, same writers) but costs money to implement. So, and this is true, IBM published two VGA standards, one with the vertical retrace interrupt, and one without it! This, of course, dictated that no interrupt became the software standard since programs could not guarantee one existed. Hardware manufactures were put into the position of building both types of cards; hence the jumpers on many VGA cards. Oh, you wonder what happened to IBM? It was purchased by a Hong Kong clothing manufacturer to insure a US market for their white shirts and ties. I think the stock is still traded on some exchange somewhere, but I've covered my kids room with the stuff. Its cheaper then most wallpaper and my children like its primary colors and the cute logo. -John_Mertus@Brown.EDU PS: All is true except the coffee story. But although I've taken liberty with the facts (aka Time Magazine), the intent is fully IBM.
(From the "Rest" of RHF)