One such technology, shingled magnetic recording (SMR), was introduced in 2013 by Seagate as "the first step to reaching a 20 TB HDD by 2020";[51] starting from the 8 TB SMR hard disk drives available in 2015, the pace of advancement would be 20% per year. Additionally, SMR comes with design complexities that may cause reduced write performance.[52][53] Other new recording technologies that, as of 2015, still remain under development include heat-assisted magnetic recording (HAMR),[54][55] microwave-assisted magnetic recording (MAMR),[56] two-dimensional magnetic recording (TDMR),[49][57] bit-patterned recording (BPR),[58] and "current perpendicular to plane" giant magnetoresistance (CPP/GMR) heads.[59][60][61]