major advantage of SCSI. The Serial ATA standard has supported native command queueing (NCQ) since its first release, but it is an optional feature for both host adapters and target devices. Many obsolete PC motherboards do not support NCQ, but modern SATA hard disk drives and SATA solid-state drives usually support NCQ, which is not the case for removable (CD/DVD) drives because the ATAPI command set used to control them prohibits queued operations. Two devices on one cable—speed impact There are many debates about how much a slow device can impact the performance of a faster device on the same cable. There is an effect, but the debate is confused by the blurring of two quite different causes, called here "Lowest speed" and "One operation at a time". "Lowest speed" On early ATA host adapters, both devices' data transfers can be constrained to the speed of the slower device, if two devices of different speed capabilities are on the same cable. For all modern ATA host adapters, this is not true, as modern ATA host adapters support independent device timing. This allows each device on the cable to transfer data at its own best speed. Even with earlier adapters without independent timing, this effect applies only to the data transfer phase of a read or write operation. "One operation at a time" This is caused by the omission of both overlapped and queued feature sets from most parallel ATA products. Only one device on a cable can perform a read or write operation at one time; therefore, a fast device on the same cable as a slow device under heavy use will find it has to wait for the slow device to complete its task first. However, most modern devices will report write operations as complete once the data is stored in their onboard cache memory, before the data is written to the (slow) magnetic storage. This allows commands to be sent to the other device on the cable, reducing the impact of the "one operation at a time" limit. The impact of this on a system's performance depends on the application. For example, when copying data from an optical drive to a hard drive (such as during software installation), this effect probably will not matter. Such jobs are necessarily limited by the speed of the optical drive no matter where it is. But if the hard drive in question