What is a .a2r file? A .a2r file is a Applesauce flux disk image, more details here: https://applesaucefdc.com/a2r/

What is a .dmg file? A .dmg file is a disk image, meaning it's an exact copy (raw block DATA) of a disk (CD, DVD, USB stick, etc...) or even just a folder wrapped in a disk image. DMG images have been the default file format for distributing software on the internet for Mac OS X users since the year 2000.  DMG images are safe to store on any partition type, such as Windows (NTFS) and are safe to distribute over FTP, send by email,...

What is a .dsk file? A .dsk file is a DiskDup image, an exact copy (sector by sector) of a floppy disk. DSK images were a popular format for cloning or duplicating 1980's and 1990's Macintosh floppy disks.   How to use or extract DSK images contents? DSK images are mountable and writeable/clonable onto real floppy disks.  Tough, remember that if you want to write a DSK image onto a real floppy disk using a Windows...

What is a .iso file? A .iso file is a disk image, meaning it's an exact copy (sector by sector) of a disk, e.g.: CD, DVD, USB stick, hard drive, etc... ISO images have been the most used file format for cloning or duplicating disks for a very long time, namely since the late 1980's along with the first consumer CD-ROM products.    How to use or extract ISO images contents? ISO images are mountable and...

What is a .mar file? A .mar file is a cross between an UNIX and a MacBinary archive.  Although a small group of individuals use it, there is no real point in using this format on Mac, except to make your archives as unlikely to be expanded by n00bs as possible.  You see, even though I'm sure that some genius, somewhere, will tell you that it's widely supported, it's hard to argue against the fact that even The Unarchiver...

What is a .rar file? A .rar file is a RAR archive, much like a ZIP file, except it's a proprietary format mostly used under the Windows environment.   How to use or extract .rar archives contents? To extract or expand a .rar archive, you simply open it with your favorite decompression tool, as it is widely supported.   Under Classic Mac OS (before Mac OS X) Mac OS 8.1 to Mac OS 9.2.2: Stuffit Expander 6.0 or...

What is a .sit file? A .sit file is a Stuffit archive, much like ZIP files today, except that .sit is a proprietary archive format from the 90's which allowed Mac users to confidently "stuff" their files, applications and documents into a flat file that could then be copied to a non-Mac hard drive partition, namely a DOS (FAT32) or Windows (NTFS) partition, without any risk of DATA corruption.  You see, throughout the...

What is a .toast file? A .toast file is a disk image of a media (CD, DVD, USB stick, hard drive, etc...) created by an application named Toast.  Note that a .toast disk image is almost exactly the same as an ISO disk image and in essence, one could absolutely rename any .toast file to .iso and use/mount it as such.  Therefore, please see this page instead: What is a .iso file (disk image) and how to use it?

What is a .woz file? A .woz file is an advanced Applesauce flux disk image, more details here: https://applesaucefdc.com/woz/  

Sometimes, you will see CD or DVD bundles for old Macs that come with both a "Software Restore" and a "Software Install" disk.  What's the difference? The software RESTORE disk will wipe the whole hard drive and reinstall everything (OS, utility apps, game demos, documentation, etc) to the factory condition.  This will leave it completely free of any previous DATA. The software INSTALL disk will let you...