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ProDOS
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ProDOS was 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, was the last official operating system usable by all Apple II series computers, and was distributed from 1983 to 1993. The other, ProDOS 16, took advantage of the extra capabilities of the 16-bit Apple , but was short-lived and replaced by GS/OS within a year.
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.
OS was released to address shortcomings in the earlier Apple operating system (called simply DOS), which was beginning to show its age.
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Encyclopedia
ProDOS was 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, was the last official operating system usable by all Apple II series computers, and was distributed from 1983 to 1993. The other, ProDOS 16, took advantage of the extra capabilities of the 16-bit Apple , but was short-lived and replaced by GS/OS within a year.
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.
Background
ProDOS was released to address shortcomings in the earlier Apple operating system (called simply DOS), which was beginning to show its age. DOS only had built-in support for 5.25" floppy disks and required patches to use peripheral devices such as hard disk drives and non-Disk II floppy disk drives, including 3.5" floppy drives. ProDOS added a standard method of accessing ROM-based drivers on expansion cards for disk devices, expanded the maximum volume size from about 400 kilobytes to 32 megabytes, introduced support for hierarchical subdirectories (a vital feature for organizing a hard disk's storage space), and supported creating a RAM disk on machines with 128K or more of memory. ProDOS addressed problems with handling hardware interrupts, and included a well-defined and documented programming and expansion interface, which DOS had always lacked. Although ProDOS also included support for a real-time clock (RTC), this support went largely unused until the release of the Apple , the first in the Apple II series to include an RTC on-board.
ProDOS, unlike earlier Apple DOS versions, had 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 were completely different from those of DOS, and ProDOS could not 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 was completely different. For this reason, most machine-language programs that ran under DOS would not work under ProDOS. However, most BASIC programs would work, though they sometimes required minor changes. A third-party program called DOS.MASTER enabled 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 Apple II model, which had long since been effectively supplanted by Applesoft BASIC and the Apple II Plus. Whereas DOS 3.3 included built-in support for BASIC programming, under ProDOS this job was given to a separate program called BASIC.SYSTEM, which one launched to run and write Applesoft BASIC programs. BASIC itself continued to be built into the Apple ROMs; BASIC.SYSTEM was merely a command interpreter that allowed BASIC programs to access ProDOS by means of the same "print Control-D" method they had used under DOS 3.3. BASIC.SYSTEM alone required about as much memory as the whole of DOS 3.3. Since the ProDOS kernel itself was stowed away in the "Language Card" RAM, the usable amount of RAM for BASIC programmers remained the same under ProDOS as it had been under DOS 3.3.
The enhanced feature set of ProDOS meant that the operating system required a minimum of 64kB of RAM (ProDOS versions up to 1.0.2 could run in 48kB but left little room for application programs - this capability was removed in version 1.1). The Apple IIe, also released in 1983, was the first Apple II computer to have 64kB of memory built in. For a while, Apple shipped both DOS 3.3 and ProDOS with new computers.
Despite ProDOS's many advantages, many users and programmers resisted it for a time because of their investment in learning the ins and outs of DOS and in DOS-based software and data formats. (A contributing reason was that ProDOS allowed only fifteen characters in a filename compared to DOS's thirty.) But Apple's integrated software package AppleWorks, released in 1984, proved a compelling reason to switch, and by the end of 1985 few new software products were being released for the older operating system. Apple IIs continued to be able to boot DOS (even the Apple IIGS could boot DOS floppies) but as 3.5" floppies and hard disks became more prevalent, most users spent the bulk of their time in ProDOS.
ProDOS was renamed ProDOS 8 when ProDOS 16 was released to support the 16-bit Apple computer, although ProDOS 16 was soon replaced by GS/OS.
Availability
ProDOS 8 requires 64kB of memory to run. The original ProDOS (8) 1.0 and 1.0.1 required only 48kB for the kernel, but nearly all programs, incluing the BASIC.SYSTEM needed to use Applesoft BASIC, required 64kB, making a 48kB system useless for ProDOS as a practical matter, and support for 48kB machines was removed in version 1.1.
ProDOS 8 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.
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 Apple Computer.
Disk support
ProDOS 8 natively supports Disk II-compatible floppy drives, a RAM drive of approximately 59kB, and "intelligent" devices with a standardized method of accepting block reads and writes. Specialized block device drivers can be hooked into the OS as well.
Filesystem
ProDOS uses the same filesystem as the earlier Apple SOS for the Apple III. The SOS/ProDOS filesystem is native to Apple SOS, ProDOS 8, ProDOS 16, and GS/OS. Some Mac OS versions also come with a file system translator to handle this filesystem.
A volume can be up to 32 megabytes, and each file can be up to 16 megabytes. Each volume (disk or hard drive partition) had a "volume name", a filename which is used as the base directory name; having two volumes with the same volume name could result in conflicts. Subdirectories are supported.
File and directory names can be 1 to 15 characters, starting with a letter then containing letters, digits, or periods. Each file entry also contains the file size; the filetype, stored as a single byte; an "aux type", a two-byte field whose function depended on the filetype; and data related to how the file is stored on the volume. Sparse files are supported.
Almost every ProDOS 8 volume has a boot sector that supports both ProDOS and SOS. This allows a disk to be used to boot on either Apple II or Apple III computers by putting both operating system kernels in the top directory: the Apple II boot sector looks for the file PRODOS and the Apple III boot sector looks for the file SOS.KERNEL.
ProDOS has no kernel support for other filesystems. 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.
External links
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- - ProDOS 8 Technical Reference Manual, wiki formatted, with FAQs, compatibility guides, etc.
- - HTML formatted
- – Apple II news and downloads
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