A 3.5 inch hard drive is a type of storage device commonly used in desktop computers. The term “3.5 inch” refers to the approximate width of the hard drive’s physical platters, though the actual dimensions are closer to 4 inches wide. These hard drives are larger in physical size compared to 2.5 inch notebook hard drives and offer more storage capacity. While the platters themselves are 3.5 inches, the whole drive enclosure is larger to accommodate the motors and control circuitry. 3.5 inch hard drives connect via Parallel ATA or Serial ATA interfaces and require an external power source. They have been the dominant hard drive form factor for desktop PCs for several decades.
History
The first 3.5 inch hard drive was introduced in 1982 by Sony.[1] Prior to this, 5.25 inch and 8 inch floppy disks were commonly used for storage. The 3.5 inch form factor allowed for greater storage capacity and portability compared to previous floppy disks. Sony’s first 3.5 inch floppy disks stored up to 720KB of data.[2]
In 1984, several companies began manufacturing 3.5 inch hard drives including Citizen, Matsushita, Maxell, Verbatim and Fuji Film. By the late 1980s, 3.5 inch floppy disks had largely replaced 5.25 inch disks as the storage medium of choice for personal computers.[1]
Overall, the 3.5 inch form factor represented a major advancement in portable data storage and capacity. The convenient size and increased storage ushered in the 3.5 inch floppy disk era during the 1980s and 1990s.
[1] https://en.wikipedia.org/wiki/History_of_the_floppy_disk
[2] https://history-computer.com/floppy-disk/
Physical Dimensions
The standard physical dimensions of a 3.5-inch hard drive are as follows:
Width: 4 inches or 101.6 mm 1
Depth: 5.75 inches or 146 mm 2
Height: 1 inch or 25.4 mm 1
The dimensions allow the 3.5-inch hard drive form factor to be commonly used in desktop computers. The size provides sufficient space for the internal components of the hard disk drive.
Weight
A typical 3.5 inch hard drive weighs between 150 and 650 grams (source). The exact weight can vary depending on factors like capacity and materials used, but most 3.5 inch drives fall within this range.
For example, common high capacity 3.5 inch hard drives can weigh around 650 grams or 1.4 pounds (source). Lower capacity drives may be lighter, with some weighing as little as 150 grams.
In comparison, smaller 2.5 inch hard drives typically weigh between 70-150 grams. So 3.5 inch drives are considerably heavier than their smaller counterparts.
The additional weight of 3.5 inch drives is due to their larger physical size, higher capacity platters, and more robust internal components. But the weight is still low enough for easy handling and installation in desktop computers and storage enclosures.
Form Factor
3.5-inch hard drives typically come in two common form factors:
- IDE (Integrated Drive Electronics) – An older parallel ATA interface standard that was widely used from the late 1980s to mid 2000s. 3.5-inch IDE hard drives are 3.75 inches wide by 1 inch high, with two IDE connectors on the back edge of the drive. They have largely been replaced by SATA drives today.
- SATA (Serial ATA) – The current serial ATA interface standard for connecting hard drives inside computers, which first appeared in 2003. 3.5-inch SATA hard drives have the same dimensions as 3.5-inch IDE drives at 3.75 by 1 inch, but have two smaller SATA connectors instead of IDE. Nearly all modern 3.5-inch hard drives use the SATA interface.
While less common, some other form factors exist like SAS (Serial Attached SCSI) used in servers and enterprise storage. But for most desktop computers and consumers, 3.5-inch hard drives will follow the IDE or SATA form factors.
Capacity
The typical storage capacity range for 3.5-inch hard drives is between 500GB to 16TB (List of disk drive form factors). As of 2019, most desktop hard drives had capacities between 1TB to 6TB, with high capacity models reaching up to 15TB (What is the upper limit of HDD storage in 3.5 inch drives?). While SSDs in the same 3.5-inch form factor may offer less total capacity, they provide faster access speeds.
Rotation Speed
The rotation speed of a hard drive, measured in revolutions per minute (RPM), determines how fast the platters spin and data can be read or written. Common RPM speeds for 3.5″ hard drives include:
- 5400 RPM – This is the slowest and most energy efficient speed for desktop hard drives. It is commonly used for low performance applications like basic data storage.
- 7200 RPM – This is the most common speed for desktop hard drives, providing better performance for typical applications while still being energy efficient.
- 10,000 RPM – This higher speed offers faster data access but with higher power consumption. It is more common for server applications.
- 15,000 RPM – Top-of-the-line enterprise hard drives spin at 15,000 RPM for maximum performance. But they require significantly more power.
For most regular computer use like gaming, multimedia, and productivity applications, a 7200 RPM drive provides the best balance of speed and efficiency. The higher RPM of 10,000 and 15,000 are only necessary for niche high-performance uses.
Power Consumption
The power draw of a 3.5″ hard drive varies depending on the capacity, rotation speed, and whether it is currently active or idle. In general, a 3.5″ HDD will consume between 5-10 Watts while active, and around 2-5 Watts while idle.
A typical 5400 RPM 3.5″ hard drive with up to 2TB capacity will use around 7 Watts during active operation and 3 Watts when idle (Source). Higher capacity and faster 7200 RPM drives tend to consume slightly more, with averages around 8-10 Watts active and 4-5 Watts idle.
Overall power draw also depends on the drive’s workload at a given moment. When the hard drive is frequently accessing data, power usage will be at the higher end of the active range. Idle power remains more consistent whether the drive is fully spun down or ready for immediate access.
Interfaces
3.5″ hard drives commonly use the following interfaces to connect to a computer or storage device:
SATA (Serial ATA): SATA is the most common interface on modern 3.5″ hard drives. SATA connections use a thin, 7-pin cable that supports transfer speeds up to 6Gb/s for SATA III drives. SATA is the interface of choice for most desktop PCs, servers, and NAS devices today.1, 2
SAS (Serial Attached SCSI): SAS is a successor to the older SCSI interface and uses a similar connector. It offers faster maximum speeds than SATA, up to 12Gb/s for SAS-3. SAS is more common in enterprise servers and SANs that require high performance.1
IDE (Parallel ATA): IDE, also known as PATA, was widely used in the past but has been mostly superseded by SATA. IDE uses a wide 40 or 80-pin cable and offers slower transfer speeds than modern interfaces. Few new drives today use IDE.3
Uses
3.5-inch hard drives are most commonly used in desktop computers, servers, and networked attached storage (NAS) devices due to their larger physical size and higher capacities compared to smaller form factor drives like 2.5-inch drives. Some key uses include:
Desktop Computers – 3.5-inch hard drives have traditionally been the default hard drive for desktop PCs, as they offer more storage capacity and the larger size is not an issue in desktop cases. High capacity 3.5-inch HDDs up to 10TB are commonly used for storage in desktops.
Servers – Enterprise and datacenter servers often utilize arrays of 3.5-inch HDDs to provide mass storage capabilities. The larger form factor allows for higher capacities compared to 2.5-inch drives.
Network Attached Storage (NAS) – NAS appliances designed for home or small office use typically use multiple 3.5-inch HDDs in RAID arrays to provide shared network storage with redundancy. The larger capacities make them well-suited for shared storage use cases.
