developed in attempt to bring the same benefits as SCSI to ATA drives. It is available in both Parallel and Serial ATA. This effort was not very successful because the ATA bus started out as a reduced-pin-count ISA bus. The requirement for software compatibility made ATA host bus adapters act like ISA bus devices without first party DMA. When a drive was ready for a transfer, it had to interrupt the CPU, wait for the CPU to ask the disk what command was ready to execute, respond with the command that it was ready to execute, wait for the CPU to program the host bus adapter's third-party DMA engine based on the result of that command, wait for the third party DMA engine to execute the command, and then had to interrupt the CPU again to notify it when the DMA engine finished the task so that the CPU could notify the thread that requested the task that the requested task was finished. Since responding to interrupts uses CPU time, CPU utilization rose quickly when ATA TCQ was enabled. Also, since interrupt service time can be unpredictable, there are times when the disk is ready to transfer data but is unable to do so because it must wait for a CPU to respond to the interrupt so that the CPU knows that it needs to program the third party DMA engine. Therefore, this standard was rarely implemented because it caused high CPU utilization without improving performance enough to make this worthwhile. This standard allows up to 32 outstanding commands per device. SATA NCQ SATA NCQ is a modern standard which drastically reduces the number of required CPU interrupts compared to ATA TCQ. Like ATA TCQ, it allows up to 32 outstanding commands per device, but was designed to take advantage of the ability of SATA host bus adapters that are not emulating parallel ATA behavior to support first party DMA. Instead of interrupting the CPU before the task to force it to program the host bus adapter's DMA engine, the hard drive tells the host bus adapter which command it wants to execute, causing the host bus adapter to program its integrated first-party DMA engine with the parameters that were included in the command that was selected by the hard drive when it was first issued, and then the DMA engine moves the data needed to execute the command. To