Apple Disk Drive S/N 2

+ Apple Disk Drive & Shugart floppy drive S/N 2 © Achim Baqué

The story of Apple Disk Drive S/N 2 is truly fascinating. In early 1978, Wendell Sander was heavily involved in the engineering of the early Apple II boards. As part of this work, he focused on testing the Disk II controller card. Because the state machine PROM could not be accessed by the processor, Sander became intimately familiar with the state machine’s operation in order to develop an effective test sequence.

During this process, he discovered that Steve Wozniak, also known as 'Woz,' had miscalculated one of the timing paths by a single count. Sander reviewed the issue with Wozniak, who agreed with the correction, and Sander created updated PROMs to fix the error.

Around the same time, Apple was ramping up Disk II production. Although many drives were ready for shipment, they encountered a significant problem: the drives failed to meet the industry-standard error rate of 1 in 10⁹, causing production delays. However, when Sander’s corrected PROMs were tested, the drives passed the error rate threshold, allowing Apple to begin shipping.

In recognition of his crucial contribution, Apple presented Sander with Disk Drive II S/N 2, which contained a Shugart floppy drive 390 S/N 2. Cliff Huston received Disk Drive II S/N 1, while Wozniak was given the Shugart 390 S/N 1.

I first saw this remarkable drive in 2018 during a visit to Wendell Sander. In December 2021, I had the privilege of acquiring this historic disk drive from him.