The most recent connection standard for mass storage devices is Serial ATA (SATA), as to be found inside many Intel Macs. Because IDE technology will reach end of life, it might be useful to consider an IDE-SATA bridge solution when it comes to a replacement that involves obtaining a new drive. Different makes are available in 3.5" and 2.5" form factor. The devices protrude a bit in lenght and/or height, compared to the usual form factor.
Where to use an IDE-SATA bridge
Most classic Macs use a hard disk drive as their main mass storage medium. Some of the latest 68k Macs and the majority of PPC Macs use IDE harddisk drives. The majority of 68k Macs uses SCSI hard disk drives of a kind not in production any more, but. Several options to replace a defective SCSI drive depend on the availability of appropriate IDE drives. Thus, a cheap converter to use most recent technology might be a good solution.
In case you need an IDE hard disk drive replacement option, be sure to check the wiki article Using Flash memory, as well.
If you have recent information about properties, additional devices or availability, update this page, please. And please: if anyone has tested one of these devices in a vintage Mac environment, please provide as much information as possible (wether the test was successful or not).