ProDOS File Format

Introduction

ProDOS (1983) is the Apple II's second disk operating system: it keeps files in 512-byte blocks, has sub-directories, dates and times, and works on 5.25-inch floppies, 3.5-inch disks (1,600 blocks, 800 KB) and hard disks of up to 65,535 blocks (32 MB). ProDOS 8 runs on the 6502 and 65C02 Apple IIs; GS/OS on the IIgs uses the same volumes. Like DOS 3.3 it is a file system, found inside a disk image: .PO, .DSK, .2MG, .HDV, .NIB or .WOZ.

A 5.25-inch ProDOS disk is 280 blocks: two ProDOS-order sectors make one block, and in a .PO file block n is at n × 512. A ProDOS disk in a .DSK file is in DOS order and its blocks are made of two sectors that are not next to each other; the explorer finds the blocks either way.

Structure

The real ProDOS volume read for this site is the ProDOS 8 utilities disk (/UTILITIES) of 1,600 blocks inside a 2IMG file: 10 files, the volume directory in blocks 2 to 5, the bitmap in block 6, 1,324 blocks free.

In the explorer

The tree shows each block (the boot blocks, directory blocks with every field of every entry, the bitmap, index blocks and the data blocks of each file by name), a picture of the volume with a square for each block, the Files table with every path, type, access, storage type, blocks, length, aux type and dates, and the directories with the chain of blocks of each. Each file opens as a node: a BAS file as an Applesoft listing, INT as Integer BASIC, BIN and SYS files disassembled at their aux address, TXT as text, others as bytes.

Not described

Known, not yet covered

• Viewer: extended files (storage type 5, GS/OS forked files) are listed but their data and resource forks are not read; the key block's two mini entries are shown only in the entry table.
• Viewer: Pascal volumes (the other use of storage type 4 and of the Apple Pascal disk format) are not read.
• Reference: the full list of GS/OS file types and auxiliary types is not given; the types page section lists the ones the viewer names.
• Viewer: the ProDOS 8 boot blocks, the GS/OS system files and the kernel are not disassembled as such: SYS files open as machine code at their aux address.

Unknown

• Reference: only two real ProDOS volumes were available (the utilities disk and an empty 800 KB demo volume). Tree files, sparse files, subdirectories, volumes of more than one bitmap block and dates after 1999 are read on built volumes only.

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