The Zombie Stack Exchanges That Just Won't Die
My parents used a Macintosh SE which they bought back in 1988 for their publishing and tutoring business. This was running System 6 and they also used to do their accounts on this machine. However since this machine cost an arm and a leg at the time and didn't feel the need to buy a new computer anyway, they kept on using it almost on a daily basis until 2003 when they bought a Sony VAIO. The mac however, I kept checking up on it and playing around with it until it finally packed in back around 2006.
As a result they gathered a large number of floppy disks, most of them 1.4 MB floppies, but most interestingly are a few System 6 disks and other software. The last time I inserted them into the machine, they still worked ok. I'm wondering what the best use of these would be. Is it worth preserving them and if so how? And how would I go about backing up the data on these disks?
Adam-E
For disks created by pre-OS X versions of Mac OS, the best solution I've found is to (1) create disk images and (2) access their contents with an emulator.
Your first priority should be to get the data off of the floppies, since they're at risk of degradation. Modern OSes can't read the System 6 filesystem even if they have a 3.5" floppy drive, so what you need is a bit-by-bit disk image of any floppies you want to save.
You might be able to create these with the SE itself, if it still works and if it has an internal hard drive and some form of network access, although I can't recommend any particular utilities. Alternatively, you can use a USB floppy drive to create images on a modern system using a utility like dd or FTK imager. A poster on the thread linked above recommended the Nippon Labs USB-FLPY-DLOCK, although I can't vouch for it myself.
One issue to be aware of is that not all 3.5" inch floppies are 1.44 MB. In the early years of 3.5" floppies there were a number of different physical formats (400kb, 800kb, single- and double-density, etc.), and not all drives were compatible with all types. A lot of the "toaster"-style Macs could only read certain varieties -- I remember this giving me headaches even at the time. If you think you might have disks in these formats, you should make sure that they are supported by whichever drive you end up using.
Once you've created the disk images, you can open and mount them in an emulator. I can't recommend a particular emulator for an SE, but I use SheepShaver to access disks created by a circa-1997 PowerTower (one of the short-lived Macintosh clones running System 7.)
Setup will depend on the particular emulator you're using, but you should be aware that pre-X versions of Mac OS, including System 6, are available for free from Apple's website. If you still have the installation disks for the software your parents used, you can take images of those and use them to install the necessary applications in the emulation environment without having to delve into the legal gray area of abandonware.
Migrating your data to a contemporary format will depend on the particular applications and might be difficult. At the cost of losing some of the formatting, you might be able to export the data into an open format (ASCII text for word processing documents, CSV for spreadsheets) that you could then open on your current system. Ideally the application itself will be able to do this, but you might have to dig around to find a file conversion utility that runs on System 6.
Once you've done all this, you can manage the disk images like you would any other files in your personal organization/backup system. If you plan to preserve this collection long-term (or to eventually store it in a formal repository), you should record any provenance/identifying information so that you know the contents and extent of what you have.
This doesn't need to be complicated -- human-readable filenames and a spreadsheet are fine -- but you should be able to identify which images came from which (physical) disks and what each image contains, even if you end up discarding the physical copies. (I.e., image "Financial_2.img" came from an 800kb Maxell floppy with a handwritten label "Financial Records Disk 2 of 6" and contains financial data for the year 1988 in ClarisWorks Spreadsheet format.)
In addition, you might want to keep a record of how to configure and set up the emulator, what the contemporary OS and hardware requirements are to run the emulator, what software (running on the emulator) is necessary to access the files, et cetera. That way, if you pass the collection on to someone else, or if you don't use it for several years and forget exactly what you did, you'll have the Representation Information (in OAIS terms) necessary to keep your data accessible.
As I mentioned, I used this process to back up and preserve the contents of a System 7 desktop. Accessing the files is as easy as booting SheepShaver and mounting the disk image, although I haven't tackled the process of exporting them to preservation formats yet.
I would also add to Nicholas' detailed answer that the type of disks you have can largely determine your imaging setup. While Mac high-density (1.4MB) disks will be easily readable and at least imageable if you have a USB floppy drive and software like dd or FTK Imager, you will not be able to image 400K (single-sided double density) or 800K (double-sided double density) disks using this setup. The reason behind this is the encoding scheme used on the disk.
High-density floppies use MFM encoding, which is supported by essentially all contemporary floppy controller boards (including those found in USB floppies, and those found on some recent motherboards). Double density Mac floppies, however, use GCR encoding, which is unsupported by most recent controllers.
To image GCR-encoded floppies using a more recent computer, you will need a board such as a KryoFlux or a Catweasel. I suggest looking at this post on libraries.stackexchange for potential guidance on which equipment to acquire (in the interest of disclosure, I have an answer on that post).
The other complicating factor in this is the file system used on the disks. If you're imaging 400K SSDD Mac disks, these disks will probably contain an MFS file system, which very few contemporary tools will read. HFS and HFS+/HFS Extended file systems are somewhat easier to read using recent tools - FTK Imager, for instance, will support reading and extracting those images.