The Advanced Host Controller Interface (AHCI) is a communication mode designed in 2004 to improve the performance and utility of SATA-connected storage devices. It was designed for HDDs and introduced a single storage request queue with a depth of up to 32 commands. This meant that HDDs could achieve higher throughput and performance, but the implementation would become a future bottleneck for SSD controller technology. For example, HDDs might be able to achieve up to 200 input/output operations per second (IOPS) where as SATA-based SSDs could reach up to 100,000 IOPS and be artificially capped in performance by the SATA bus.