SATA
Serial ATA (SATA) is a computer bus interface that connects storage devices (such as hard disk drives (HDDs), solid-state drives (SSDs), and optical drives like CD/DVD/Blu-ray drives) to the motherboard in a computer system. Its primary purpose is to transfer data between the storage devices and the rest of the computer.
SATA was designed to replace the older Parallel ATA (PATA) interface, which was the standard for connecting storage devices for many years. The "Serial" in its name refers to the method of data transfer, where data is sent bit by bit over a single pair of wires, as opposed to PATA's method of sending multiple bits simultaneously over many parallel wires.
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Overview
SATA offers several advantages over its predecessor, PATA. The most significant improvements include faster data transfer speeds, simpler and thinner cables that allow for better airflow inside a computer case, and support for features like hot-swapping (connecting or disconnecting devices while the system is running).
Due to its widespread adoption, SATA has been the standard interface for most internal storage devices in desktop computers, laptops, and servers for well over a decade. While faster interfaces like NVMe are becoming common for high-performance SSDs, SATA remains prevalent for larger capacity HDDs and many mainstream SSDs.
History and Evolution
SATA was first introduced in 2003, replacing PATA. Since its introduction, the standard has evolved through several generations, primarily increasing the maximum data transfer throughput:
- SATA 1.0 (SATA I): Introduced with a maximum theoretical throughput of 1.5 Gbit/s (gigabits per second), which translates to approximately 150 MB/s (megabytes per second) after accounting for encoding overhead.
- SATA 2.0 (SATA II): Introduced with a maximum theoretical throughput of 3 Gbit/s (approx. 300 MB/s).
- SATA 3.0 (SATA III): Introduced with a maximum theoretical throughput of 6 Gbit/s (approx. 600 MB/s). This is the most common version found in modern computers.
- SATA 3.2 (SATA Express): An attempt to integrate PCIe into the SATA standard to increase speed (up to 16 Gbit/s), but it did not see widespread adoption compared to the direct rise of NVMe over PCIe.
Each new version of SATA is backward compatible with older versions, although the speed will be limited to the capabilities of the slower device or port.
Advantages over PATA
SATA provided significant improvements when it replaced PATA:
- Higher Throughput: Initially faster, and subsequent generations increased the speed advantage.
- Thinner, More Flexible Cables: PATA used wide ribbon cables; SATA uses thin, seven-pin data cables, improving airflow and ease of installation.
- Simpler Connectors: Smaller and easier to connect than PATA's large, 40-pin or 80-pin connectors.
- Hot-Swapping Support: SATA supports hot-swapping (connecting or disconnecting devices while the computer is running), a feature not standard with PATA.
- Lower Voltage: Uses lower signaling voltages, reducing power consumption.
Comparison to NVMe
While SATA was a major step up from PATA, it was designed when HDDs were the primary storage. Its protocol and speed limits (stalling at 600 MB/s) became a bottleneck for SSDs, whose flash memory can operate much faster. NVMe is a newer interface designed specifically for the speed of flash memory.
NVMe connects SSDs directly to the CPU via PCIe lanes, offering significantly higher Throughput (thousands of MB/s) and lower Latency compared to SATA's shared bus and protocol overhead. Therefore, for maximum SSD performance, NVMe is preferred over SATA.
Connectors and Form Factors
SATA uses distinctive L-shaped connectors:
- SATA Data Connector: A 7-pin L-shaped connector used for data transfer.
- SATA Power Connector: A 15-pin L-shaped connector used to supply power to the drive. It replaced the older 4-pin Molex connector used by PATA drives.
SATA drives come in standard form factors:
- 2.5-inch: The standard size for laptops and increasingly common in desktops and servers, used by most SSDs.
- 3.5-inch: The standard size for desktop HDDs.
- Optical Drive Form Factors: CD, DVD, and Blu-ray drives typically use SATA connectors.
- mSATA: A smaller form factor using the SATA protocol, typically for small SSDs in laptops or embedded systems (largely replaced by M.2).
- M.2: A compact form factor used for both SATA and NVMe SSDs (check specifications to know which protocol it uses).
