Revolution in the Valley: The Insanely Great Story of How the Mac Was Made by Andy Hertzfeld

Author:Andy Hertzfeld [Hertzfeld, Andy]
Language: eng
Format: epub
Tags: Business & Economics, General, Industries, Computers & Information Technology, Workplace Culture, Research & Development, Computers, Operating Systems, Macintosh, Hardware
ISBN: 9780596007195
Google: 6ASeeTZbqCQC
Amazon: 1449316247
Publisher: O'Reilly Media
Published: 2005-09-14T16:00:00+00:00

Quick, Hide In This Closet!

by Andy Hertzfeld in August 1983

A Twiggy diskette

In 1980, Apple reorganized again, splitting off a new "Disk Division" headed by John Vennard, responsible for developing a hard disk code-named "Pippin" and a next generation floppy disk code-named "Twiggy". Both were intended to be used first by the Lisa project, and eventually across Apple's entire product line. At Rod Holt's request, I had written some early diagnostics for Twiggy using an Apple II, but I felt lucky that they asked Rich Williams instead of me to transfer to the disk division as their software guy, since focusing exclusively on disks seemed pretty limiting.

Woz's Apple II floppy disk design was way ahead of the rest of the industry, so Apple felt confident that it could continue to innovate to extend its lead. Twiggy was a fairly ambitious project, more than quadrupling the capacity of standard floppy disks by doubling the data rate (which required higher density media) and employing other innovative tricks like motor speed control, which slowed down the disk rotation speed on the outer tracks to cram more data on them.

The Lisa was designed to include two built-in Twiggy drives, so it made sense for the Macintosh to use Twiggy as well. Twiggy used a Woz-style disk controller, which created a problem for the Lisa designers, since that required exact timing from the microprocessor and therefore couldn't tolerate interrupts, which was perhaps OK for a simple system like the Apple II but was unacceptable for a more sophisticated system like Lisa. Instead, the Lisa hardware designers (Paul Baker, Bob Paratore and others) solved the problem by including a little Apple II, with its own memory and microprocessor (but clocked twice as fast), inside the Lisa to control the Twiggy drives.

The Lisa also supported an optional, external hard drive through a built-in parallel port. As the Twiggy designers encountered unexpected difficulties in achieving an acceptable error rate, Lisa came to rely on the hard drive instead. The Twiggy drive was also slower than expected, because of the high error rate as well as the way the variable motor speed trick increased seek times, since you had to wait for the speed change to stabilize. Besides, the Lisa operating system designers were used to working on systems that swapped memory from disk, which wasn't really feasible to pull off at floppy disk speeds. Soon, the hard disk became mandatory, upping the minimum price of a Lisa by more than a thousand dollars.

Lisa was announced to great fanfare in January 1983, but it still wasn't ready to ship. There were problems in a number of areas, but the biggest one was the low yield of the Twiggy drives, whose high error rate greatly limited production. Finally, Lisas were shipped to customers in June 1983, even though there continued to be production and reliability problems with the disk drives.

Meanwhile, the Mac team was beginning to panic. We were using a single Twiggy drive as our floppy disk, and we didn't have a hard disk to fall back on.

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