Hard drives are vital components in computers and other devices that allow us to store large amounts of data. The interface between the hard drive and the rest of the computer is what allows data to be transferred back and forth. There are several different types of hard drive interfaces that have been used over the years. In this article, we will look at the most popular and widely used hard drive interfaces.
ATA/IDE
ATA, also known as IDE (Integrated Drive Electronics), is one of the oldest and most widely used hard drive interfaces. It was first introduced in the 1980s and remained the primary hard drive interface for PCs throughout the 1990s and early 2000s.
ATA interfaces connect hard drives to the computer’s motherboard using wide ribbon cables. The cables transfer data parallelly, with each cable having 40 or 80 wires to carry bits of data. ATA interfaces have gone through several iterations over the years, with each version boosting performance:
- ATA-1 – Supports up to 16MB/s transfer rates
- ATA-2 – 33MB/s transfer rates
- ATA-3 – 66MB/s transfer rates
- ATA/66 – 66MB/s transfer rates
- ATA/100 – 100MB/s transfer rates
- ATA/133 – 133MB/s transfer rates
One advantage of ATA interfaces is that they are inexpensive to implement. However, their parallel data transfer and ribbon cables limit their effectiveness for fast data transfers over long distances. As serial interfaces were introduced, the popularity of ATA started to decline in the mid-2000s.
SATA
Serial ATA, or SATA, is now the most popular hard drive interface used in modern PCs. SATA was introduced in 2001 to replace the older parallel ATA interfaces. Here are some key advantages of SATA compared to PATA:
- Faster transfer speeds – SATA interfaces provide faster data transfer through serial communication, reaching speeds of up to 600MB/s.
- Thinner cabling – SATA uses much thinner 7-pin cables instead of wide 40-pin ribbons cables, improving cable management and airflow inside a computer.
- Longer cable lengths – SATA cables can be up to 1 meter long, compared to only 18 inches for ATA cables.
- Hot swapping – SATA devices can be connected and disconnected without rebooting the computer.
There have been several generations of SATA interfaces over the years:
- SATA 1.0 – First SATA version introduced in 2003, provides 150MB/s transfer speeds.
- SATA 2.0 – Released in 2004, up to 300MB/s transfer speeds.
- SATA 3.0 – Released in 2009, up to 600MB/s transfer speeds.
- SATA 3.1 – Introduced in 2017, supports up to 1969MB/s transfer speeds.
- SATA 3.2 – Released in 2019, supports up to 1969MB/s transfer speeds.
The thick ribbon cables and slower transfer speeds of older ATA interfaces made them unsuitable for the faster PC systems and larger storage capacities that emerged in the 2000s. SATA has replaced ATA as the de facto standard for hard drive interfaces on new computers and storage devices.
USB
The Universal Serial Bus (USB) interface is also used for some external hard drives and flash-based storage devices. While not as fast as SATA, USB is a popular interface option due to its near-universal connectivity with computers and consumer devices.
USB storage devices are powered directly by the USB cable, eliminating the need for external power sources. They can be easily swapped between different machines with USB ports. However, the interface is better suited for lower capacity drives that do not need very fast data transfer speeds.
There are several versions of the USB standard providing different maximum data transfer rates:
- USB 1.0 – Released in 1996, up to 12 Mbps transfer speeds.
- USB 2.0 – Introduced in 2000, up to 480 Mbps speeds.
- USB 3.0 – Released in 2008, up to 5 Gbps transfer rates.
- USB 3.1 – Introduced in 2013, up to 10 Gbps speeds.
- USB 3.2 – Released in 2017, up to 20 Gbps transfer rates.
While USB may not match the raw speed of SATA interfaces, its convenience and wide compatibility make it a popular option for external storage devices. Most computers and mobile devices produced in the last decade contain USB ports, making it easy to connect USB drives.
SCSI
The Small Computer System Interface (SCSI, pronounced “skuzzy”) is a high-speed interface that allows connection of multiple storage devices. SCSI interfaces were widely used for hard drives, tape drives, CD-ROM drives, and other devices beginning in the 1980s.
Some key characteristics of SCSI interfaces:
- High speeds – SCSI interfaces provide very fast data transfer rates, well above 100 MB/s.
- Multiple device connectivity – A single SCSI controller can support up to 8 or 16 devices on a bus.
- Wide cable formats – SCSI cables contain many parallel wires to enable fast transfers, up to 68 or 80 wires.
However, SCSI interfaces also have some downsides. The cables and controllers required are more expensive than SATA or ATA. SCSI devices usually require setting jumpers or device IDs for proper configuration. And the parallel cables limit the cable length between devices.
The speed and multiple device support of SCSI made it popular for servers, networks, and RAID arrays where very high disk performance was needed. But for regular hard drives in desktop PCs and laptops, SCSI has been superseded by SATA for the most part.
SAS
Serial Attached SCSI (SAS) is another interface used primarily in servers and high-end workstations. As its name indicates, it provides a serial version of the SCSI interface. SAS was introduced in 2004 as a replacement for older parallel SCSI.
Some advantages of SAS compared to parallel SCSI:
- Much faster signal transfer through serial connectivity
- Thinner, more flexible cables
- Longer cable lengths supported
- Full-duplex communication
The latest SAS-3 standard provides 12 Gbit/s transfer speeds per channel. And multiple channels can be aggregated for even faster speeds. SAS offers excellent performance for tasks like video editing, databases, simulations, and other demanding applications.
However, the cost of SAS interfaces and drives makes them prohibitively expensive for typical home or office PCs. SAS remains confined mainly to servers and high-end workstations that need the absolute fastest hard drive performance currently available.
NVMe
NVM Express, also known as NVMe, is the newest interface option designed specifically for solid state drives (SSDs). Traditional interfaces like SATA were created before SSDs existed and are not optimized for these much faster storage devices.
NVMe provides several advantages for communicating with SSDs in PCs and servers:
- Much higher transfer speeds – NVMe provides several performance “gears” with maximum throughput around 4 GB/s.
- Lower latency for faster responses.
- Designed for parallelism with up to 64K queues and 64K commands per queue.
- Efficient command set tailored for non-volatile memory.
With its very high speeds and low latency, NVMe is the ideal interface for taking full advantage of the incredible performance of today’s SSDs. NVMe drives are standard in high-end gaming PCs and workstations. They are also found in enterprise servers and arrays where maximizing SSD performance is crucial.
The catch is that NVMe requires NVMe-capable ports on the motherboard or a dedicated PCIe adapter card. So NVMe has high performance but narrower compatibility than ubiquitous interfaces like SATA and USB.
U.2
U.2, formerly known as SFF-8639, is an interface that allows NVMe SSDs to be used in servers and workstations that were designed for SAS connectivity. Basically U.2 is a connector standard that allows an NVMe drive to plug into a SAS port.
Some key details about U.2:
- Supports the latest NVMe drives
- Uses a 2.5 inch form factor
- Connector is mechanically identical to SAS/SATA
- Bandwidth up to PCIe Gen3 x4
U.2 is basically a bridging standard between NVMe and SAS. It provides backwards compatibility for systems with SAS/SATA backplanes and bays. Companies can gradually transition their products to NVMe without having to completely redesign their hardware ecosystems.
M.2
M.2 is a form factor specification for SSDs designed to replace older mSATA and mini-PCIe interfaces in laptops, tablets, and other devices where space is at a premium.
Some key characteristics of M.2 SSDs:
- Compact “gumstick” card shape
- Small physical size – 22mm x 30mm, 22mm x 42mm, or 22mm x 60mm
- PCIe and/or SATA host interfaces
- Supports NVMe for maximum performance
The tiny physical footprint of M.2 combined with the performance of NVMe makes this form factor perfect for ultrabooks and other compact mobile computing devices. M.2 slots are standard on most modern notebook PCs.
M.2 SSDs are also showing up more frequently in high-end desktops and all-in-one PCs where space is limited. Their small size allows them to fit easily into tight confines where a traditional 2.5″ or 3.5″ SSD would not.
CFexpress
CFexpress is one of the newest interfaces on the market, leveraging the PCIe and NVMe standards for cameras and other devices needing fast data capture.
Key features of CFexpress include:
- Utilizes PCIe 3.0 x2 or x4 interfaces
- NVMe protocol support
- Up to 8 GB/s data transfer speeds
- Low latency
- Small, rugged form factor
- Backward compatible with select older devices
CFexpress devices are targeted primarily at high-end cameras for ultra fast recording of high-resolution photos and videos. But the interface could potentially have applications in other data-intensive embedded systems that need tiny, durable solid state storage.
Thunderbolt
Thunderbolt is not exclusively a storage interface, but rather a hardware interface standard that can connect peripherals using both PCIe and DisplayPort protocols. But Thunderbolt’s high speeds make it well suited for external storage.
Key features of Thunderbolt include:
- Very high bandwidth – Currently up to 40 Gbps.
- Low latency
- Daisy chainable, allowing multiple peripherals to connect through one port.
- Can carry both data and display signals
- Compatible with PCIe and DisplayPort devices
Thunderbolt has gone through several iterations since being introduced in 2011. The latest Thunderbolt 4 standard doubles bandwidth to 40 Gbps while remaining backward compatible with previous Thunderbolt devices.
Thunderbolt gives users an extremely fast and flexible way to connect devices like high-res displays, RAID arrays, network adapters, and external SSDs. It provides near-direct access to the PCIe bus, minimizing throughput issues caused by other interfaces.
The downside to Thunderbolt is that it has not been widely adopted outside of Apple devices and higher end PCs. But for devices that require the absolute lowest latency and lag-free display performance, Thunderbolt is currently unbeaten.
Comparison Table
| Interface | Year Introduced | Max. Speed | Uses |
|---|---|---|---|
| ATA/IDE | 1980s | 133 MB/s | Internal hard drives |
| SATA | 2003 | 1969 MB/s | Internal hard drives |
| USB | 1996 | 20 Gbps | External drives, flash drives |
| SCSI | 1981 | 1280 MB/s | Hard drives, tape, CD/DVD drives |
| SAS | 2004 | 12 Gbps | Enterprise hard drives |
| NVMe | 2011 | 4 GB/s | Solid state drives |
| U.2 | 2016 | 4 GB/s | Enterprise SSDs |
| M.2 | 2013 | 4 GB/s | Compact SSDs |
| CFexpress | 2017 | 8 GB/s | High-speed cameras |
| Thunderbolt | 2011 | 40 Gbps | External devices |
Conclusion
While older interfaces like ATA/IDE and SCSI paved the way, SATA has clearly emerged as the most popular hard drive interface for desktop PCs, laptops, and consumer devices. Its balance of speed, compatibility, affordability and ease-of-use make it ideal for the vast majority of systems.
However, SATA is likely nearing the end of its useful lifespan. The exponentially faster NVMe standard has already taken over the high-performance space to fully leverage the speed of solid state drives. NVMe and associated form factors like M.2 and U.2 seem poised to eventually replace SATA as the next dominant hard drive interface across all platforms.
Looking to the future, we can expect even faster versions of NVMe, as well as improvements to pioneering interfaces like Thunderbolt. Transfer speeds that once seemed impossibly fast just a few years ago, like 32Gbps and 64Gbps, are already on the horizon. There is still plenty of room for innovation when it comes to the interfaces that connect our insatiable computing devices to equally fast storage.
