What is and how does the IDE interface work on PC

In the history of the PC, many interfaces and types of connectors have been used, because as the industry has evolved, more modern and faster interfaces have been adopted. Today we are going to tell you what the IDE interface is and how it works, something that although today it has already disappeared in home PCs, it has been widely used for many years and, in fact, is still used in some industrial areas.

As you know, in the world of PC hardware interfaces are the connection methods between components. For example, PCI-Express is an interface, as is USB or SATA since they are ways to connect some components with others (although it is generally to connect a component to the motherboard).

What is the IDE interface and what does it consist of?

Parallel ATA (PATA), originally AT Attachment and also known as ATA or IDE, is a standard interface created by Western Digital and Compaq in 1986 to connect hard drives and CD / DVD drives to the motherboard of a PC, although it was also used a variant to connect floppy drives. The standard is still maintained by the X3 / INCITS committee and uses the underlying ATA and ATAPI (AT Attachment Packet Interface) standards.

The term IDE comes from Integrated Drive Electronics, because it was the name Western Digital gave it when it developed this interface, and storage drives with that interface had a maximum size limit of 137 GB.

Indeed, we are talking about that elongated interface with many connectors (39 or 40 depending on the device) that the hard drives and optical drives of yesteryear had and whose cable was gray, flat, and elongated with the pins individually isolated. Unlike the Serial ATA standard, and as the name suggests, the connectors work in parallel, allowing more than one device to be connected in a single cable.

Obviously, the motherboards had this 40-pin connector to be able to connect the cables, which went to the hard drives and optical drives in the same way as we now connect the SATA data cables. By the way, these units had the peculiarity that they were powered by MOLEX 4-pin connectors from the power supply instead of modern SATA connectors.

History and terminology of the IDE interface

The standard was originally conceived as "AT Bus Attachment", officially called AT Attachment and abbreviated as "ATA" because its main feature was a direct connection to the 16-bit ISA bus introduced by IBM. When the SATA interface was introduced in 2003, the original ATA was renamed Parallel ATA or PATA for short.

ATA physical interfaces became a standard component on any PC, initially on host bus adapters, sometimes on a sound card, but finally as two physical interfaces built into the motherboard's SouthBridge. Called "primary" and "secondary" or "master" and "slave" ATA interfaces, they were assigned to base addresses 0x1F0 and 0x170 on ISA bus systems.

These are the existing types or generations:

• IDE and ATA-1: The first version of what is now known as ATA / ATAPI was developed by Western Digital. The first devices to use it were Compaq and they were released in 1986.
• EIDE and ATA-2: This standard was approved in 1994, and the EIDE name stands for Enhanced IDE.
• ATAPI:  initially the interface was developed for storage devices, but ATAPI allowed to take the ATA interface further and be used in other types of devices since it allowed the "eject" command, so it was ideal for floppy drives, for example. It also incorporated the SCSI command.
• UDMA and ATA-4:  This standard raised the performance to 33 MB / s, and in its latest versions new 80-pin cables were incorporated that increased the performance up to 133 MB / s.
• Ultra ATA:  Initially described by Western Digital in 2000, this interface described higher performance but never really saw the light of day because it coincided with the days of SATA, which ended up replacing the IDE interface.

Master and slave disks, how did they work?

The current SATA interface works in series, so it is not possible to connect more than one device with the same data cable, but the IDE interface, being in parallel, did allow it. However, when two devices were connected with the same cable, one should be designated as device 0 (Master) and the other as device 1 (slave). This distinction was necessary to allow both units to share the same data cable without conflict, and it was made with the famous jumper incorporated in hard drives and optical drives of the time.

Device 0 is the drive that will appear first in the BIOS and will be used to boot the operating system; In other words, you could have the operating system installed on two hard drives and change which one to boot from just by changing the position jumper on both drives to select a primary and a secondary one. This forced PCs that had an IDE interface and a single hard disk to have the jumper in the Master position, because otherwise the BIOS did not know where the PC had to boot from, although that was solved in later versions with a special configuration called "Single".