IDE drives were the first ones to popularise integrating the logic controller onto the hard disk itself. This change corrected many of the problems that had been associated with hard disks up to that point, such as poor signal integrity, complexity and the need for every controller to be "generically" capable of dealing with any hard disk. The very first hard disks to have integrated controllers weren't technically using the IDE/ATA interface as we currently know it. They were in fact so-called "hardcards", which were designed and sold by the "Plus Development" division of Quantum. These devices were simply 3.5" hard disks that were mounted directly to a controller card that plugged into an ISA expansion slot.

While an ingenious idea--one that basically put Quantum "on the map" in the hard disk world--these hardcards had several problems. Hard disks are heavy, and are mechanical devices. They just aren't well-suited to being mounted in expansion slots like a video card or modem. Physical support for expansion cards is poor, because they are held in place using just one screw; this resulted in vibration issues. The width of the drive would typically block off at least one additional bus slot, meaning one of these devices took two expansion bus slots. Cooling was also sometimes a problem. Of course, all of these are physical implementation issues, and don't detract from the significance of the advance in integrating the controller and disk assembly.

It didn't take long until manufacturers realised that there was really no reason to keep the hard disk physically on the controller at all. They decided to put the controller on the bottom of the hard disk and move the entire hard disk and controller assembly to a regular drive bay. The connection to the system bus was maintained through the use of a cable that ran either directly to a system bus slot, or to a small interfacing card that plugged into a system bus slot. In many ways, then, these drives were connected directly to the ISA system bus. The official name for the interface, "AT Attachment", reflects this, as the IBM PC/AT was the first PC to use the now-standard 16-bit ISA bus.
As system and hard disk performance improved, the slow speed of the ISA bus became an issue, so interface cards--often called controller cards, despite the confusion that this causes--were created for the higher speed VESA local bus, and then the PCI bus. Today, all modern PCs have their IDE/ATA interface attached directly to the PC bus.

The next evolution of how IDE/ATA drives interface to the system occurred when it became obvious that every PC was going to have a hard disk, and it was therefore silly to waste an expansion slot even on a hard disk interface card. Chipset manufacturers began integrating IDE/ATA hard disk controllers into their chipsets, so that instead of connecting the drives to a controller card, they were connected directly to the motherboard. With this change, integration of the interface was complete, with all the logic either on the motherboard, or the hard disk itself. This is the technique that is used today, though one can still add a physical controller card if necessary.