Serial ATA (SATA) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. SATA provides a serial link that supports data transfer speeds up to 6 Gbit/s. The key questions answered in this article are:
- What is Serial ATA?
- How is Serial ATA different from Parallel ATA?
- What are the advantages of Serial ATA?
- What are the different versions and speeds of SATA?
- How is a SATA connection made?
- What devices use SATA?
- What cables and connectors are used with SATA?
What is Serial ATA?
Serial ATA (SATA) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. SATA is part of the SATA/PATA family of interfaces. It originated from the Parallel ATA (PATA) interface, with the primary difference being that SATA uses serial signaling instead of parallel signaling. This allows for reduced cable size, cost and complexity.
The SATA host adapters and devices communicate via a high-speed serial cable. Data is transmitted in serial fashion bit by bit along a lane one cable, rather than in parallel across multiple cables. The thinner serial cable allows for improved cable routing and management compared to PATA. SATA operates point-to-point between devices, rather than daisy-chained.
History of SATA
The SATA specification was first announced in August 2001 by the SATA IO organization, with the intent to replace the older PATA standard. The developers aimed to provide several specific advantages over PATA, including reduced cable size and cost, native hot swapping, faster data transfer through higher signaling rates, and more scalable performance to satisfy growing data storage demands.
The original SATA 1.0 specification provided for a maximum bandwidth of 1.5 Gbit/s. Subsequent revisions have improved the maximum data transfer rate up to 16 Gbit/s for the latest SATA 3.4 specification released in 2017.
How is Serial ATA different from Parallel ATA?
While SATA devices and PATA devices function in a similar role and may look alike, there are some key differences between Serial ATA and Parallel ATA technologies:
Signaling Method
The primary difference between SATA and PATA is the signaling method:
- SATA – Uses serial signaling, transmitting data sequentially one bit at a time over a single cable.
- PATA – Uses parallel signaling, transmitting multiple bits at the same time over 40 or 80 separate wires in a wide flat ribbon cable.
Cable Size
Due to the signaling methods:
- SATA cables are thin (about 0.25 inch wide) and flexible, with seven conductors.
- PATA cables are wide ribbons up to 2 inches across, requiring large connectors.
Connectivity
The connectivity models differ:
- SATA – Point-to-point connections between one device and the host.
- PATA – Daisy-chained configuration, where devices connect to each other in sequence.
Hot Swapping Support
Due to the connectivity methods:
- SATA – Natively supports hot swapping, allowing devices to be connected and disconnected while powered without rebooting.
- PATA – Does not directly support hot swapping.
Transfer Speeds
SATA features much faster potential data transfer speeds than PATA:
- SATA – Started at 1.5 Gbit/s, currently up to 16 Gbit/s for latest specification.
- PATA – Max bandwidth of 133 Mbit/s.
What are the advantages of Serial ATA?
Serial ATA provides several advantages over the older Parallel ATA technology:
Thinner Cables
The thin SATA cables allow for easier cable routing and improved airflow and cooling within a computer system compared to wide PATA ribbons.
Hot Swappability
SATA natively supports hot swapping, so SATA devices can be attached or detached without rebooting the computer. This avoids downtime during storage upgrades or replacement.
Simplified Cabling
PATA cables had to be connected in a daisy chain, so swapping cable order affected Master/Slave relationships. SATA uses point-to-point connections for simplified cabling.
Scalable Performance
SATA has scaled interface speeds up to 16 Gbit/s to satisfy growing data storage needs, while PATA was limited to 133 Mbit/s max bandwidth.
Cost Effectiveness
The simpler SATA cabling and connectors reduce manufacturing costs compared to PATA.
No Master/Slave Configuration
Unlike PATA, SATA does not require tricky Master/Slave configuration, since it uses point-to-point links.
Efficient Use of PCI Slots
PATA host adapters typically required two PCI slots, while SATA needs just one PCI slot on the motherboard.
What are the different versions and speeds of SATA?
There have been several revisions of the SATA specification, each designated by its theoretical signaling speed:
SATA 1.0 (1.5 Gbit/s)
- Released in 2003
- First SATA specification
- Bandwidth up to 1.5 Gbit/s (150 MB/s)
SATA 2.0 (3.0 Gbit/s)
- Released in 2004
- Bandwidth up to 3.0 Gbit/s (300 MB/s)
SATA 3.0 (6 Gbit/s)
- Released in 2009
- Also called SATA 6G or SATA III
- Bandwidth up to 6 Gbit/s (600 MB/s)
SATA 3.2 (16 Gbit/s)
- Released in 2016
- Also called SATA Express
- Uses PCI Express and SATA cables
- Bandwidth up to 16 Gbit/s (1969 MB/s)
SATA 3.3 (24 Gbit/s)
- Released in 2017
- Also called SATA Express (2x)
- Bandwidth up to 24 Gbit/s (2918 MB/s)
SATA 3.4
- Released in 2019
- Current latest SATA specification
- Bandwidth up to 16 Gbit/s
In practice, sustained data transfer speeds are below the specified maximums due to protocol overhead and other factors. Still, each revision delivers substantially higher performance capability over previous generations.
How is a SATA connection made?
A SATA connection between a host adapter and storage device involves both physical cables/connectors and logical communication protocols. Here is an overview of the SATA connection components:
Physical Connection
- One or more SATA cables connect between the SATA host adapter and SATA device.
- Low-voltage differential signaling (LVDS) is used to transmit data over the cables.
- Cables have 7-pin connectors on each end that plug into SATA ports on devices.
Logical Link
- Point-to-point serial link is established between the host and device.
- Link initialization and management follows the SATA protocol specification.
- Hot plugging is supported using transmit ready (TRDY) and receiver detect (RDY) handshaking.
- Link power management mode enables partial or slumber power savings.
Transport Layer
- Responsible for transmitting and receiving native SATA frames of FISes (Frame Information Structures).
- Maintains 8b/10b encoding scheme for DC balance and error detection.
- Handles frame sequencing, ACK/NAK, CRC checks, and retry control.
Application Layers
- Map SCSI or ATA commands onto encapsulated FIS frames.
- Task File provides registers to send commands, logical block addressing, and data to/from device.
- SATA is compatible with legacy ATA software drivers and applications.
Together, this full protocol stack enables robust transmission of storage commands, status, and payload data between the host and device.
What devices use SATA?
Some common devices that use Serial ATA connections include:
Hard Disk Drives (HDDs)
Common hard drives connect via SATA to store and retrieve data from spinning magnetic platters. Enterprise HDDs may use multiple SATA ports.
Solid State Drives (SSDs)
SSDs containing flash memory chips connect via SATA. Their fast access speeds benefit from SATA 3.0+ throughput.
Optical Disc Drives
CD, DVD, and Blu-Ray disc drives typically use a SATA interface for connectivity.
RAID Controllers
RAID controller cards enable multiple SATA HDDs to be configured in RAID arrays for redundancy or speed.
External Enclosures
External docking stations and disk enclosures connect to host PCs via eSATA extension cables.
Other Devices
Some removable storage devices, tape drives, multimedia devices, network attached storage, and other peripherals may interface over SATA.
What cables and connectors are used with SATA?
SATA physical connections utilize cables, connectors, and port interfaces including:
SATA Cables
- Typically 7-pin shielded cables up to 1 meter long
- Thinner than PATA ribbons
- Low-voltage differential signaling
- Locking clip optionally prevents accidental disconnects
SATA Data Connectors
- “L” shaped 7-pin connectors plug into SATA ports
- Usually latching type to prevent loose connections
- Keyed shape prevents upside down insertion
SATA Power Connectors
- 15-pin larger connector for device power needs
- May be straight or right-angled shape
- Provides 3.3V, 5V, and 12V supply lines
SATA Ports
- Host bus adapters and devices have SATA ports
- Typically numbered 0, 1, 2, etc to identify individual ports
- May be SATA 150, 300, 600, etc to indicate speed
Using this cabling infrastructure, SATA provides a robust point-to-point serial link for storage devices to interface with the host system.
Conclusion
In summary, Serial ATA is a widely used server and computer interface designed to replace the older Parallel ATA connections. SATA provides many advantages for modern computing storage needs, including faster speeds, simpler cabling, hot swapping capability, and scalability to satisfy growing data demands. The serial protocol, thin cables and compact connectors make SATA ideal for connecting high-performance HDDs, SSDs, and optical drives.