The size and type of storage memory that you will need to store your signals depends, of course, on the size of the signal files, but it also depends on what you are going to do with the information.
Purchase considerations:
Personal recommendation: after using external hard disks, CDs, Zip disks, Syquest cartridges, and MO disks, I will stay with the Zip disks and 640M MO cartridges. These are the only media that have withstood both being dropped accidentally and a ride in my briefcase on the back of my motorbike. (MacWorld actually tested Zip drives by throwing them against the wall--the disks passed with 'flying' colors.) The 100M Zips are a little small for my use (the new 250M's look attractive), and a full 640M MO is slow to mount when full, but not worrying about the integrity of my files is worth the wait.
Many options are now available at continually dropping prices:
If you are looking for a way to move just a few files, then floppy disks are still a good way to go for most people. Remember that floppy drives are a separate purchase item for the iMacs and new G3's, though, so make sure the machine the disk is headed for can receive it.
If you are looking for a disk to keep a backup copy of your main hard disk, an external hard disk is a good way to go. This is recommended in case your System becomes corrupted or your internal hard disk dies. In 11 years I've only had 2 hard disks die on me, but both time it resulted in a loss of a couple of days work. I also have not had an entire System become corrupted for quite some time, but it has happened in the past--I now have 2 hard disks, each with 2 partitions with System Folders on them, just in case, and an extra backup copy of all of my files on MO disk.
The newer 'wide SCSI' hard disks, often requiring a wide SCSI PCI card installed, are much, much faster than the older, standard SCSI drives. If speed is a big concern for you, you should definitely investigate them.
Removable media are perhaps the best way to go for storage of many large files, including signals. Their price has dropped substantially in the last year, making them a very good alternative to an external hard disk. Why continue to stack external hard disk drives on your desk when you can have one removable media drive on your desk and a stack of disks on your shelf? In addition, each non-removable external hard drive requires its own power supply and its own cable to attach it to your SCSI chain; in contrast, a removable media drive requires one power supply and one cable connection for all of your disks.
What type of removable media to buy depends a lot on what the current prices are. As of the writing of this file, the price per Mb of storage for removable hard disks (Zip, Jazz and Syquest disks) and MO disks was about the same; the average access times for removable hard disks was slightly faster, but not significant unless your are transferring very large data files.
When you make your decision, be sure to shop around for the best price of each type of drive, and don't forget to check the availability and price of the disks themselves.
If you are looking for a way to archives large data collections, be they the data from your experiment or a database of the project you are distributing, CD-ROMs are the way to go. With a capacity of about 650Mb and an estimated shelf life of 100 years, CD's provide the capacity and permanence most anyone would want. And the recordable (and now, read/write/rewrite) drives are coming down in price almost daily.
However, the time it takes to learn to master a CD is probably prohibited for most individual use. (Next year, I'll make the time...)
The same goes for DVD drives, except that they hold much more information than a standard CD. However, they haven't been around long enough for the prices to drop far enough for most individuals.
Tape drives are also probably only of use to those who need to make more permanent archives of material. The speed of these drives when you are looking for a file is limited by the fact that the drive must spool through the tape to reach its destination. They might also be worth investigating though, since the technology on all fronts continues to develop.
<Space for future links to info files and/or vendors--any suggestions?>