History First drive was called the RAMAC. Actually, it held 5 million 7-bit characters. Hard drive was designed to replace drum memory. Univac would have shipped a disk drive in 1956 too. But they didn't want to mess up their drum memory business. Alan Shugart was involved in the project. He left IBM to go to Memorex. Then he founded Shugart Associates, making floppy drives. Then he was fired. Then he founded Shugart Technologies with Finis Conner. Which was renamed Seagate. Then Conner left to found Conner. Seagate bought Conner in the late 1990s. RAMAC platters were limited to 24 inches, so the system would fit through standard doors. This was standard practice with IBM. === Physical Layout === Hardware Interfaces Seagate ST-506 was introduced in 1980. First PC hard drive. Capacity of 5 MB. Seagate ST-412 was used in the IBM PC XT. Capacity of 10 MB. Same basics as the ST-506. Modern drives have both a read and write head on the same arm, not a single head. ATA broke 137 GB limit with 48-bit LBA. ST-506 interface has 2 cables -- one for data, one for control. ESDI - Enhanced Small Device Interface. ATA - AT Attachment Block transfer mode PIO, DMA, UltraDMA