The Apple Disk II, first released in June 1978 about a year after the Apple II computer, is a great story of a genius inventor outsmarting The Man to deliver affordable disk-based storage to the masses, liberating them from the tyranny of slow and cumbersome linear cassette-based storage. It’s a great story. Some of it is even true.
The legend of the Apple Disk II
According to legend, Mike Marukkula asked Steve Wozniak to design a disk drive system for the Apple II because tape was too slow. Steve Jobs and Woz balked at the $390 price of standard 5.25-inch Shugart SA400 drive mechanisms. So Jobs approached Shugart (a Xerox subsidiary, which became an important relationship) and sought to purchase bare drive mechanisms without any drive electronics at a discount. Shugart didn’t want to sell bare mechanisms, so they tried to pull a fast one and included defective drive mechanisms in the shipment to discourage them.
Woz had never designed a disk interface before. But working through the end of 1977, including on Christmas Day and New Year’s Day in order to have the prototype ready at the Consumer Electronics Show in January 1978, he came up with something that made sense to him and only needed five chips. It worked, and proved simpler and cheaper than the standard Shugart interface other computers used. Additionally, he found encoding the disks with Group Coded Recording rather than the more conventional FM encoding Shugart used yielded 30% more data on the disk.
The drive cost Apple $140 to build.
The design required a disk interface that plugged into an available slot on the motherboard (slot #6 was the typical choice) and then connected to a corresponding board on the drive mechanism itself via a 20-conductor ribbon cable. Misaligning or reversing the cable was easy to do, which could damage the drive, any disk inserted in the drive, or both.
Outsmarting Shugart
Shugart’s plan was to frustrate Apple by selling defective drive mechanisms. Since the drives had various problems, they would yield inconsistent results and likely frustrate an inexperienced engineer.
But in the end it only slowed Apple down. Woz got his prototype working after making minor adjustments to one of the drive mechanisms. Some of the mechanisms needed more extensive repair. Apple engineer Cliff Huston developed procedures to repair the drives on the assembly line. Apple put the Disk II into production using the bare Shugart mechanisms, slapped Wozniak’s PCB on them, and sold them. No one was the wiser that Shugart had shipped Apple defective product.
And before long, Apple was back at Shugart, asking for more drives, the Disk II became necessary equipment, and helped the Apple II sell 6 million units over its lifetime. Apple later switched to Alps drives, which had an outwardly similar appearance but were less expensive. Apple went on to become the first trillion-dollar company in the world, greedy Shugart liquidated in 1986, and capitalism worked.
Where the story falls apart
But that’s where the legend starts to fall apart. If you pre-ordered the Disk II, it cost $495. Its retail price ended up being $595, which is $2,957 in 2025 dollars, and more than a 4x markup from its build cost. Also in 1978, Radio Shack delivered its Mini Disk, a disk drive for its TRS-80 using a conventional design, and priced it at an outrageous sum of… $499.
Radio Shack’s pricing tells us Apple wasn’t passing the savings from Woz’s design onto consumers like a latter-day Robin Hood. It was still an expensive peripheral for an expensive computer.
The Apple drive stored 113K compared to Radio Shack’s 85K, but by 1979, inexpensive double density MFM controllers hit the market, doubling the capacity of competing drives. So Apple’s competitive advantage in that regard was short-lived. In 1980, Apple revised the design to increase the capacity to 143K and make it more competitive. The change came at the expense of being able to autoboot off bootable 113K floppies, but the increased capacity was worth that sacrifice and came early enough in the machine’s life to not be ruinously disruptive.
The Apple II and Zork
Occasionally on social media, someone states that the Apple Disk II’s (lack of) capacity was the reason Infocom split Zork, originally a single game running on DEC PDP-10 mainframes and PDP-11 minicomputers, into three installments. I think that’s a bit of an urban legend or possibly even an AI hallucination. That’s because the first computer Infocom bought was a TRS-80, not an Apple II. The Apple II was Infocom’s second target platform.
Infocom knew the game’s original 1977 implementation was too big to port directly to the TRS-80 or Apple II as-is. But Infocom initially intended to split Zork in two, not three. Then Zork II proved too big, so they split Zork II into two parts, yielding the third installment. But the reason was really the size of microcomputer floppy disks in general, not the Apple II specifically.
David Farquhar is a computer security professional, entrepreneur, and author. He has written professionally about computers since 1991, so he was writing about retro computers when they were still new. He has been working in IT professionally since 1994 and has specialized in vulnerability management since 2013. He holds Security+ and CISSP certifications. Today he blogs five times a week, mostly about retro computers and retro gaming covering the time period from 1975 to 2000.