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PATA and SATA: The evolution of disk standards

Disk standards have evolved over time, and while PATA and IDE may have reliability on their side, growing support and advancements for SATA may make it the preferred option.

I've been working with storage systems -- from one-off PCs to midrange Unix systems and everything in between -- since the 1980s, and in that time, there have been a tremendous number of advancements in data storage. In those early days, I recall working with disks that were massive in size, if not capacity. These cabinet-based disks had unique connectivity capability but eventually gave way to newer standards, such as PATA and SATA.

Ultimately known as Parallel Advanced Technology Attachment, Integrated Drive Electronics (IDE) featured a 40-pin connector that was capable of transferring 16 bits at a time and was the first generation of drives to use the PATA interface. A later variant, while retaining a 40-pin form factor, used 80 individual conductors to transmit data. However, only 39 of the pins were actually used, as 80-conductor systems eliminated one of the physical pins to make it easier to figure out which direction the cable should be inserted.

PATA was not just a single standard; it was a series of evolving standards that improved as new generations of technology hit the market. IDE/PATA is still in use today, although most recent development is taking place with technologies that provide enhanced support for new types of media, such as flash storage.

In the early 2000s, as hard drive speeds and sizes continued to increase, Advanced Host Controller Interface (AHCI) joined IDE as an interface option and brought with it a new type of connection known as Serial ATA (SATA). From a purely physical perspective, SATA had a number of benefits over PATA -- most notably, eliminating the massive 40-pin ribbon connector in favor of a much smaller connector and cable. This served to simplify storage connectivity and, inside PC cases, made routing cabling far easier and improved airflow.

Integrated Drive Electronics (IDE)

PATA vs. SATA

The difference between PATA and SATA may appear to be just one letter, but there are real improvements that have been made with SATA. Most notably, SATA devices can transfer data at speeds that far surpass what was possible with PATA. Even SATA's slowest speed is faster than PATA's fastest, which, in a world in which even desktop storage performance counts, is really important when choosing between PATA and SATA.

Back when SATA and AHCI -- the software layer that enables the OS to communicate with SATA devices -- were introduced, getting OS support for AHCI was more difficult, but today, every OS of import has full support for AHCI and SATA devices.

SATA and PATA

In a single computer, even if it uses SATA, you're often able to configure the SATA port to operate in an IDE mode. This can be useful if your OS doesn't support AHCI, but again, that's not much of a problem today. This ability to emulate the older IDE is a key trick that you can use should you encounter a system that doesn't support AHCI.

But AHCI provides so many more benefits that you should use it whenever possible.

The difference between PATA and SATA may appear to be just one letter, but there are real improvements that have been made with SATA.

First and foremost, AHCI supports Native Command Queuing (NCQ) and the ability to hot swap hardware while a system is running. NCQ provides performance improvements thanks to its ability to more granularly manage read and write operations to and from media. The ability to reduce the distance that the read and write heads of spinning disks need to travel results in lower storage latency since data can be read and written more quickly. AHCI supports a single storage queue, but that queue can hold up to 32 commands.

So, while the raw throughput upgrade is one way in which AHCI and SATA are faster than older IDE storage devices, NCQ adds another dimension to the PATA and SATA debate. This combination helps to reduce bottlenecks in two places in the storage pathway -- across the wire itself and at the controller.

As newer storage options, such as flash storage, continue to expand in the market, this controller becomes a bottleneck. This is being addressed through the introduction of nonvolatile memory express (NVMe), a construct that replaces AHCI. With support for 64,000 command queues, each of which can support 64,000 commands, NVMe is purpose-built to support SSDs and the ability of that media to read and write simultaneously to different parts of the media at an exceptionally fast rate.

In terms of modern PATA and SATA products, you don't see a lot of physical IDE on the market today. However, it is still in play in older systems and as one of SATA's and AHCI's operating modes.

This was last published in July 2018

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