Editing Apple II (section)

===The OS Disk===
Apple and many third-party developers made software available on tape at first, but after the Disk II became available in 1978, tape-based Apple II software essentially disappeared from the market. The initial price of the Disk II drive and controller was US$595, although a $100 off coupon was available through the Apple newsletter "Contact". The controller could handle two drives and a second drive (without controller) retailed for $495.

The Disk II single-sided floppy drive used 5.25-inch [[floppy disk]]s; double-sided disks could be used, one side at a time, by turning them over and notching a hole for the write protect sensor. The first [[disk operating system]]s for the {{nowrap|Apple II}} were {{nowrap|[[Apple DOS|DOS 3.1]]}} and DOS&nbsp;3.2, which stored 113.75&nbsp;KB on each disk, organized into 35 tracks of 13 256-byte sectors each. After about two years, DOS&nbsp;3.3 was introduced, storing 140&nbsp;KB thanks to a minor firmware change on the disk controller that allowed it to store 16 sectors per track. (This upgrade was user-installable as two PROMs on older controllers.) After the release of DOS&nbsp;3.3, the user community discontinued use of {{nowrap|DOS 3.2}} except for running legacy software. Programs that required DOS&nbsp;3.2 were fairly rare; however, as DOS&nbsp;3.3 was not a major architectural change aside from the number of sectors per track, a program called MUFFIN was provided with DOS&nbsp;3.3 to allow users to copy files from DOS&nbsp;3.2 disks to DOS&nbsp;3.3 disks. It was possible for software developers to create a DOS&nbsp;3.2 disk which would also boot on a system with {{nowrap|DOS 3.3}} firmware.

Later, double-sided drives, with heads to read both sides of the disk, became available from third-party companies. (Apple only produced double-sided 5.25-inch disks for the Lisa 1 computer).

On a DOS 3.x disk, tracks 0, 1, and most of track 2 were reserved to store the operating system. (It was possible, with a special utility, to reclaim most of this space for data if a disk did not need to be bootable.) A short ROM program on the disk controller had the ability to seek to track zero{{snd}} which it did without regard for the read/write head's current position, resulting in the characteristic "chattering" sound of a Disk II boot, which was the read/write head hitting the rubber stop block at the end of the rail – and read and execute code from sector 0. The code contained in there would then pull in the rest of the operating system. DOS stored the disk's directory on track 17, smack in the middle of the 35-track disks, in order to reduce the average [[seek time]] to the frequently used directory track. The directory was fixed in size and could hold a maximum of 105 files. Subdirectories were not supported.

Most game publishers did not include DOS on their floppy disks, since they needed the memory it occupied more than its capabilities; instead, they often wrote their own boot loaders and read-only file systems. This also served to discourage "crackers" from snooping around in the game's copy-protection code, since the data on the disk was not in files that could be accessed easily.

Some third-party manufacturers produced floppy drives that could write 40 tracks to most 5.25-inch disks, yielding 160&nbsp;KB of storage per disk, but the format did not catch on widely, and no known commercial software was published on 40-track media. Most drives, even Disk IIs, could write 36 tracks; a two byte modification to DOS to format the extra track was common.

The Apple Disk II stored 140&nbsp;KB on single-sided, "single-density" floppy disks, but it was very common for Apple II users to extend the capacity of a single-sided floppy disk to 280&nbsp;KB by cutting out a second write-protect notch on the side of the disk using a "disk notcher" or hole puncher and inserting the disk flipped over. Double-sided disks, with notches on both sides, were available at a higher price, but in practice the magnetic coating on the reverse of nominally single-sided disks was usually of good enough quality to be used (both sides were coated in the same way to prevent warping, although only one side was certified for use). Early on, diskette manufacturers routinely warned that this technique would damage the read/write head of the drives or wear out the disk faster, and these warnings were frequently repeated in magazines of the day. In practice, however, this method was an inexpensive way to store twice as much data for no extra cost, and was widely used for commercially released floppies as well.

Later, Apple IIs were able to use 3.5-inch disks with a total capacity of 800&nbsp;KB and hard disks. {{nowrap|DOS 3.3}} did not support these drives natively; third-party software was required, and disks larger than about 400&nbsp;KB had to be split up into multiple "virtual disk volumes."

DOS 3.3 was succeeded by [[Apple ProDOS|ProDOS]], a 1983 descendant of the Apple ///'s SOS. It added support for subdirectories and volumes up to 32&nbsp;MB in size. ProDOS became the {{nowrap|Apple II}} DOS of choice; [[AppleWorks]] and other newer programs required it.