Hard drive technology is relatively ancient (in terms of computer history, anyway). There are well-known pictures of the infamous IBM 350 RAMAC hard drive from 1956 that used 50 24-inch-wide platters to hold a whopping 3.75MB of storage space. This, of course, is the size of an average 128Kbps MP3 file today, in the physical space that could hold two commercial refrigerators. The IBM 350 was only utilized by government and industrial users, and was obsolete by 1969. Ain't progress wonderful? The PC hard drive form factor standardized at 5.25 inches in the early 1980s, with the 3.5-inch desktop-class and 2.5-inch notebook-class drives coming soon thereafter. The internal cable interface has changed from serial to IDE (now frequently called parallel ATA, or PATA) to SCSI to serial ATA (SATA) over the years, but each essentially does the same thing: connect the hard drive to the PC's motherboard so your data can be processed. Today's 2.5- and 3.5-inch drives mainly use SATA interfaces (at least on most PCs and Macs), though some high-speed SSDs use the faster PCIe interface instead. Capacities have grown from multiple megabytes to multiple terabytes, more than a million-fold increase. Current 3.5-inch hard drives have capacities as high as 10TB, with 2.5-inch drives maxing out at 4TB.