(FORTUNE Magazine) – IT'S EVERY CONSUMER'S DREAM. You want to make a major purchase, like a car or a computer. You're after high quality at a reasonable price, and you know exactly the features you want. So you call a manufacturer and place an order. Instantly, a modern factory sets to work and custom-builds your machine for delivery to your door within a week. (Roll over, Henry Ford!) Don't expect Detroit to offer this service anytime soon, but you can get it today from Dell Computer, the No. 1 direct marketer of PCs. The build-to-order system isn't just a recent addition meant to help the company, based in Austin, Texas, compete in the please-the-consumer Nineties. Dell has specialized in custom PCs since 1984, when founder Michael Dell got his start assembling machines in his college dorm room. Though Dell lost $36 million last year, partly because of a failed third try at selling notebook computers, its Burger King assembly lines for desktop machines are the envy of the industry. Compaq Computer, Dell's archrival in Houston, is restructuring its entire logistics operation in hopes of achieving similar manufacturing flexibility by 1996. Dell hasn't forgotten Henry Ford completely. Lately it has expanded into the retail arena, where merchants typically order hundreds of the same model PC. So Dell has jiggered some assembly lines to handle bulk orders. John Varol, director of manufacturing operations, says, We call it mass customization, and it's a lot easier than sending hundreds of orders down the line.'' Dell's new notebook computer (the company's fourth try at the market) is mass-produced by AST Research. But PCs built to order still account for over 90% of Dell's $2.9 billion in annual sales. FORTUNE followed one machine from the moment a customer ordered it until Dell delivered it 46 hours, 42 minutes later. MEANWHILE, ON THE PRODUCTION FLOOR. . .