PRODOS is the name of two similar operating systems for the Apple II
series of personal computers . The original ProDOS, renamed PRODOS 8
in version 1.2, is the last official operating system usable by all
ProDOS was marketed by Apple as meaning PROFESSIONAL DISK OPERATING SYSTEM, and became the most popular operating system for the Apple II series of computers 10 months after its release in January 1983.
* 1 Background
* 2 Requirements
* 2.1 Unlicensed
* 3 Availability
* 4 Disk support
ProDOS was released to address shortcomings in the earlier Apple operating system (called simply DOS ), which was beginning to show its age.
Apple DOS only has built-in support for 5.25" floppy disks and
requires patches to use peripheral devices such as hard disk drives
and non-Disk-II floppy disk drives, including 3.5" floppy drives.
ProDOS adds a standard method of accessing ROM-based drivers on
expansion cards for disk devices, expands the maximum volume size from
about 400 kilobytes to 32 megabytes, introduces support for
hierarchical subdirectories (a vital feature for organizing a hard
disk's storage space), and supports RAM disks on machines with 128kB
or more of memory. ProDOS addresses problems with handling hardware
interrupts , and includes a well-defined and documented programming
and expansion interface, which
Apple DOS had always lacked. Although
ProDOS also includes support for a real-time clock (RTC), this support
went largely unused until the release of the
ProDOS, unlike earlier Apple DOS versions, has its developmental roots in SOS , the operating system for the ill-fated Apple III computer released in 1980. Pre-release documentation for ProDOS (including early editions of Beneath Apple ProDOS) documented SOS error codes, notably one for switched disks, that ProDOS itself could never generate. Its disk format and programming interface are completely different from those of Apple DOS, and ProDOS cannot read or write DOS 3.3 disks except by means of a conversion utility; while the low-level track-and-sector format of DOS 3.3 disks was retained for 5.25 inch disks, the high-level arrangement of files and directories is completely different. For this reason, most machine-language programs that run under Apple DOS will not work under ProDOS. However, most BASIC programs work, though they sometimes require minor changes. A third-party program called DOS.MASTER enables users to have multiple virtual DOS 3.3 partitions on a larger ProDOS volume.
With the release of ProDOS came the end of support for Integer BASIC
and the original
Despite ProDOS's many advantages, many users and programmers resisted
it for a time because of their investment in learning the ins and outs
Apple DOS and in Apple-DOS-based software and data formats. A
contributing reason was that ProDOS allows only 15 characters in a
filename compared to Apple DOS's 30. But Apple's integrated software
All editions of ProDOS require an
ProDOS 8 requires 64kB of memory to run. The original ProDOS (8) 1.0
through 1.0.2 requires only 48kB for the kernel, but nearly all
programs, including the BASIC.SYSTEM needed to use
ProDOS 8 version 2.x requires a 65C02 or later (65802, 65816) CPU . ProDOS 8 2.x runs in 64kB, but the utility programs on the system disk require 128kB. Systems with a 6502 CPU instead of a 65C02 must use ProDOS 8 versions prior to version 2.0.
The unofficial "ProDOS 8 2.4," released on August 16, 2016, removes
the 65C02 requirement and will run on all
ProDOS 16 requires an
UNLICENSED APPLE II CLONES
With the release of ProDOS version 1.01 and higher, a check was added
to see if it was running on an official Apple-manufactured computer.
If the word "Apple" is found in the computer's ROM firmware, ProDOS
will load up as normal. If anything else is found (e.g. "Golden",
"Franklin", "Elite") ProDOS refuses to run, locking up at the boot
splash screen. This measure was taken by
ProDOS system disk images can be downloaded legally from a number of
user group web sites. It can also be purchased on disk from Syndicomm,
which distributes it under license from
ProDOS 8 natively supports Disk II -compatible floppy drives, a RAM drive of approximately 59kB on computers having 128K or more RAM, and block devices whose controllers support the Pascal firmware protocol, a standardized method of accepting block reads and writes originally introduced for use with the UCSD p-System . This latter category includes 3.5" disk and hard drives. Custom block device drivers can be hooked into the OS as well.
ProDOS uses the same file system as the earlier
Apple SOS for the
A volume is allocated in 512-byte blocks. (5.25" floppy disks are still formatted using 256-byte sectors, as this is the format required by the controller ROM to boot the disk. ProDOS simply treats pairs of 256-byte sectors as a single block on such drives.) A volume can have a capacity of up to 32 megabytes, and each file can be up to 16 megabytes. Each volume (floppy disk or hard drive partition) has a "volume name", a filename which is used as the base directory name; having two volumes with the same volume name can result in conflicts. If necessary, ProDOS searches all available drives to find a named volume. Subdirectories are supported, and the concept of a "prefix" (working directory or current path) was provided to make working with subdirectories easier.
File, directory, and volume names can be 1 to 15 characters, starting with a letter, then containing more letters, or digits or periods. Each file entry also contains the 16 bit (2 byte) pointer to the block containing the beginning of the file (or its block index); a 16-bit block count; a 24-bit (3-byte) file size; an 8-bit (1-byte) filetype ; a 16-bit auxiliary type (the meaning of which depends upon the filetype); creation and modification timestamps ; and data related to how the file is stored on the volume. Sparse files are supported, but files are never "sparsified" by removing zero-filled blocks. The volume header contains similar information as relevant to volumes.
Directories (including the root directory) are sequentially indexed, with each block starting with the address of the previous block (or zero if none) and the subsequent block (or zero if none). The root directory on most disks is initialized to 4 blocks, allowing 51 entries (excluding the volume header). It never changes in size, except by manual intervention with special tools. Subdirectories begin at one block, and grow automatically as needed.
Normal files are progressively indexed. Single-block files (under 513
bytes) have no index block; the directory entry points directly to the
block of file data. Files with between 2 and 256 blocks (513 bytes to
128 kB) of data have a single index block, to which the directory
entry points, which contains a list of up to 256 data block addresses.
Larger files have a master index block containing a list of up to 256
index block addresses. When the
The volume has a bitmap of used blocks. Other than this, there is no central file allocation table .
A ProDOS 8 volume formatted by Apple's tools has a boot sector that
supports booting both ProDOS and SOS depending on what computer it is
booted on. Block 0 is the
ProDOS has no kernel support for other file systems. If necessary, a conversion utility on the main system disk is used to transfer files individually between ProDOS and older Apple DOS 3.3 disks. Because they use a different low-level disk format than DOS 3.3 and ProDOS, transferring data from DOS 3.2 disks to ProDOS is a two-step process using a DOS 3.3 disk as an intermediary (utilizing the DOS 3.3 utility MUFFIN or similar).
* ^ Weyhrich, Steven (2001-07-07). "Chapter 15: DOS 3.3, ProDOS &
* Don Worth and Pieter Lechner. Beneath Apple ProDOS. Quality Software, Chatsworth, California, 1984. ISBN 0-912985-05-4