An internal hard drive is a data storage device located inside a computer that stores digital content like documents, media files, software programs, and the operating system (OS). It connects to the motherboard using an interface like SATA, SAS, or M.2. The main platters inside a hard drive spin at high speeds to read/write data using a read/write head
Hard drives were first introduced by IBM in 1956, with capacities less than 5 MB. Over the decades, capacities and performance have vastly improved. Today’s internal consumer hard drives have capacities from 500GB to multiple terabytes. Common uses include as the primary drive to boot the OS and store files, or as additional internal mass storage in desktops and laptops.
Key defining characteristics of an internal hard drive are that it is a non-volatile storage device, meaning it retains data when powered off, and that it has high capacity compared to faster solid state drives. Hard drives are less expensive per gigabyte compared to SSDs, making them well-suited for mass storage.
Common Internal Hard Drive Form Factors
Internal hard drives come in two main physical sizes: 2.5-inch and 3.5-inch. These sizes refer to the diameter of the disks inside the drive enclosure, not the outer dimensions of the drive itself.
3.5-inch drives are most commonly used in desktop computers, while 2.5-inch drives are designed for laptops. 3.5-inch drives typically offer more storage capacity, with common sizes ranging from 500GB to 10TB. 2.5-inch drives range from 320GB to 2TB for mainstream laptop drives. Enterprise and high performance drives are available in larger capacities for both form factors.
3.5-inch hard drives use a Parallel ATA (PATA) interface or serial interfaces like SATA and SAS. Common dimensions are 4″ x 5.75″ x 1″ for a typical 3.5″ desktop drive. 2.5-inch drives use the SATA interface primarily and measure 2.75″ x 3.95″ x 0.374″ for a standard 9.5mm thick laptop drive.
Overall, the main factors in choosing internal drive form factors are physical size, storage capacity, and interface. Desktops take 3.5″ drives while laptops use 2.5″ drives. 3.5″ offers more storage while 2.5″ prioritizes smaller size.
SATA (Serial AT Attachment) is the most popular interface for hard drives today. SATA was developed to replace the older PATA (Parallel ATA) interface, with the main advantages being higher transfer speeds and thinner cables (Wikipedia).
There have been several revisions of the SATA interface over the years:
- SATA 1.0 – 1.5 Gbit/s
- SATA 2.0 – 3 Gbit/s
- SATA 3.0 – 6 Gbit/s
- SATA 3.1 – 16 Gbit/s
- SATA 3.2 – 22.5 Gbit/s
The most common SATA connectors are:
- SATA Data – for data transmission
- SATA Power – for power transmission
Newer SATA revisions are backwards compatible, so SATA 3 drives can be used on SATA 2 controllers. However, maximum performance requires matching controller and drive interfaces.
The Parallel ATA (PATA) interface, also known as IDE (Integrated Drive Electronics), was the primary hard drive interface used in personal computers from the late 1980s until around 2003. PATA drives connected to the motherboard via a 40-pin or 80-wire ribbon cable and powered by a 4-pin molex power connector.
PATA drives have much larger cables compared to newer interfaces like SATA, which allowed for shorter cable lengths and smaller form factors. The wider PATA ribbon cable was necessary to support 16 data lines for transferring data, compared to only 7 lines for SATA. PATA was originally introduced as an 8-bit interface, then evolved to 16-bit (ATA-2) and 32-bit (ATA-3).
Common PATA connector types include 40-pin (for 3.5″ drives), 44-pin (for 2.5″ drives), and 80-wire (for dual drives). The connector endpoints were color coded, with pin 1 indicated by a missing pin. Master/slave jumpers were used to configure two drives on one cable. PATA drives were limited to transfer speeds up to 133 MB/s.
While PATA has mostly been replaced by SATA in modern systems, it was the primary hard drive interface during the rise of personal computing. PATA drives are still used today in some industrial applications that require IDE compatibility.
The Serial Attached SCSI (SAS) interface is commonly used in enterprise servers and high-performance workstations where fast data transfer speeds are required (HP, 2019). SAS is a point-to-point serial protocol that supports data transfer rates of up to 12 Gbit/s. The SAS interface uses a much smaller cable connector than traditional parallel SCSI, which allows for faster signaling and more device connections via expanders.
Some key characteristics and uses cases for SAS drives include:
- High performance – SAS offers much faster interface speed compared to SATA, making it well-suited for applications like video editing, 3D modeling, simulations, etc. where large files are constantly read from and written to disk.
- Reliability – SAS drives support advanced error checking features to ensure data integrity.
- Scalability – SAS allows connecting multiple drives using expanders, enabling large storage capacities.
- Hot swappability – SAS drives can be replaced and added to a system without powering it down.
- Dual porting – SAS drives provide redundancy by allowing a connection via two separate controller ports.
Overall, the SAS interface excels in enterprise environments where performance, reliability and scalability are critical requirements. It is the interface of choice for most server storage and high-end workstations.
mSATA, which stands for Mini-SATA, is a smaller form factor SSD (solid state drive) that is designed for use in portable and power-constrained devices such as laptops, tablets, and netbooks (Source). mSATA drives are about one quarter the size of a standard 2.5 inch SATA SSD drive, making them well-suited for small and thin mobile devices where space is limited.
The mSATA interface uses the SATA protocol to connect the SSD drive to the host system, but in a much smaller footprint. mSATA drives typically measure about 1.8 inches x 3/4 inch x 1/8 inch in size. This compact design allows them to fit into an mSATA slot on the motherboard of a laptop or tablet. mSATA drives offer similar performance, capacities, and features as full-sized SATA SSDs, just in a smaller physical package.
Some typical applications for mSATA drives include ultrabooks, netbooks, laptops, and tablet PCs where minimizing space and power consumption are important factors. The small size and low power draw of mSATA drives make them well-suited for these mobile platforms. mSATA SSDs are commonly used as the primary internal storage drive or as additional internal storage in space-constrained devices.
M.2, also known as Next Generation Form Factor (NGFF), is a small form factor interface designed for internal drives and expansion cards like SSDs. M.2 uses the PCI Express and Serial ATA interfaces over a single connector to provide high bandwidth and reduce clutter. It was introduced in 2013 and has become a popular standard for internal SSDs.
M.2 modules come in different physical lengths like 2230, 2242, 2260, 2280, and 22110 which denote their dimensions in mm. They also use different keying notches like M keyed for PCIe SSDs, B keyed for SATA SSDs and BM keyed for SATA and PCIe SSDs. The keying prevents inserting an M.2 drive in an incompatible slot. Popular M.2 interfaces include PCIe 3.0 x4 and SATA 3.0.
Overall, the small footprint, high speed and versatility of M.2 has led to wide adoption. It allows manufacturers to easily integrate high-performance storage without taking up space for drive bays (https://en.wikipedia.org/wiki/M.2).
NVMe, which stands for Non-Volatile Memory Express, is a protocol specification designed specifically for solid state drives (SSDs). It was created to address the shortcomings of older interfaces like SATA and SAS in fully utilizing the speed of SSDs.
The key benefit of NVMe over SATA is much higher performance. As per Netapp, NVMe enables SSDs to perform at speeds up to 6-7x faster than SATA SSDs. This is because NVMe utilizes the high bandwidth of PCIe lanes (up to 64 Gbps), while SATA is still bottlenecked at 6 Gbps.
In addition, NVMe has improved queuing and Stream capabilities to better manage multiple I/O requests in parallel. This allows NVMe SSDs to fully saturate the PCIe bus bandwidth and minimize latency.
Overall, for tasks involving heavy workloads and frequent read/write operations, NVMe provides substantially higher throughput and lower latency compared to SATA SSDs.
Choosing the Right Internal Hard Drive
When selecting an internal hard drive, there are several key factors to consider including capacity, speed, form factor, and interface.
Capacity refers to the amount of data the drive can store, with common sizes ranging from 120GB to 4TB for laptop drives and up to 10TB for desktop drives. It’s important to consider how much storage you need for applications, media files, and other data (Source).
Speed determines how quickly the drive can read and write data. This is measured in revolutions per minute (RPM) for traditional hard disk drives and read/write speeds for solid state drives. Faster drives offer better system performance but come at a higher cost (Source).
Form factor refers to the physical size and shape of the drive. Common internal form factors include 3.5″ for desktops and 2.5″ for laptops. Drives must match the form factor supported by the computer case or laptop (Source).
The interface determines how the drive connects to the computer’s motherboard. Common interfaces include SATA, SAS, and M.2. It’s crucial to choose a drive with a compatible interface supported by the system (Source).
By evaluating these factors, you can select the best internal hard drive for your performance needs and budget.
When choosing an internal hard drive format, the most important factors to consider are the interface, physical size, and performance needs. SATA remains the most common interface for 3.5″ and 2.5″ hard drives meant for desktops and laptops. mSATA and M.2 offer more compact form factors well-suited for ultrabooks and mini PCs where space is limited. NVMe M.2 drives provide cutting-edge bandwidth and IOPS for high-performance computing applications.
Looking to the future, we can expect new interfaces and form factors to emerge for internal storage as computing devices continue getting smaller and more powerful. However, SATA will likely persist for years to come as the standard for budget-friendly mass storage. M.2 and NVMe will become increasingly dominant in high-end PCs and servers needing top sequential and random access speeds. The physical size and connector of internal drives will evolve, but the need for locally attached storage will remain.