These common formatting options exist for hard drives and flash drives, which you may see, and are usable in the manner suggested:
1. ExFAT for non-Mac bootable but Mac 10.6.5 read/write hard drives that can boot XP SP 2 or higher.
2. FAT32 for non-Mac bootable, but any Mac OS read/writable 4 GB and under drives you can use with any version of Windows to boot Windows.
3. NTFS for non-Mac bootable, but any Mac OS read-only without third party software larger hard drives you can use with any version of Windows to boot Windows. Tuxera NTFS, Google's Macfuse, and Paragon Software NTFS-Mac are three options for making it writable by Macs.
4. HFS+/GUID to boot Intel Macs, but not boot Windows, and not be readable by PowerPC Macs (pre-2006 601, 603, 604, G3, G4, G5). Macdrive needed to read from Windows without a network.
5. HFS+/Apple Partition Map /Journaled to boot PowerPC Macs with Mac OS X 10.2.3 or later if the Mac is older than the operating system, but not Windows. Macdrive needed to read from Windows without a network.
6. HFS+/Apple Partition Map/not Journaled to boot any PowerPC Mac with Mac OS 8.1 or later if the Mac is older than the operating system, but not Windows. Macdrive needed to read from Windows without a network.
7. HFS Standard to boot Mac OS 8.0 or earlier Macs. Macdrive needed to read from Windows without a network.
You are only likely to run into 1 through 4 today.
Very rarely will 5 - 7 appear.
For CDs and DVDs, you are likely to run into
1. The wrong thickness, size or shape.
2. Joliet and UDF which is supported by (the now defunct) Software Architect's ReadDVD in situations where the Mac operating system can't handle it directly.
If you find a need to read this format, you may find this software in areas that sell older software and computers.
3##ISO-9660 which is 100% crossplatform.
4 Formatted specifically for Mac files, which can't be read by Windows.
Make sure you understand the data utilities you use and how they format or partition the discs in question to ensure your drive or disc is able to be used in the environment you desire. Many of the Windows formatting solutions here work better when Windows is installed on a Mac.
5 To date, no Mac has been built with Bluray support built-in. See this tip if you wish to use Bluray.
6 Standard movie DVDs can open with Apple's DVD Player. Extras that are playable on a computer as an application either need InterActual's DVD Player, or to run Windows as is stated in item 3 above.
For both if the PRAM battery is over 4 years old, external devices and optical discs may start failing to work even before the system clock doesn't work properly anymore.