ST-506 can refer to either the hard disk drive (HDD) or its interface The ST-506 hard disk drive was the first 5.25 inch hard disk drive, introduced in 1980 by Shugart Technology (now Seagate Technology). It stored up to 5 megabytes after formatting and cost US $1,500 ($4,308 in today's dollars). The similar, 10-megabyte ST-412 was introduced in late 1981. The ST-225 was introduced shortly thereafter with 20 megabytes and half the height. All three used MFM encoding, a widely used coding scheme. A subsequent extension of the ST-412 interface used RLL encoding for a 50% increase in capacity and bit rate.