The hardware component responsible for storing your digital content in a persistent way on your computer is the well-known hard drive. Sometimes you will hear the term “non-volatile” storage, which means that even if you power off the system the hard drive still keeps the stored data in it.
Hard drives come in different capacity sizes, types and connection interfaces. In this context, “size” refers to storage capacity and not the physical dimensions of the drive.
You cannot save programs, pictures, documents, or other personal files without a hard drive. The OS itself is installed on the hard disk.
Can a computer operate without a hard drive? A computer will only power up without a hard drive, but it cannot run without a properly functioning storage system.
Hard disks can reside inside or outside a computer. Internal hard disks are connected directly to the motherboard of a computer system (e.g laptop, workstation, server etc).
On the contrary, external hard drives are connected to the system using a wired interface such as thunderbolt or a USB cable.
In this article we will discuss and explain different types of computer hard disks and also different types of interfaces used to connect a hard drive to the rest of the computer eco-system.
Let’s start with the 3 most popular types of hard disk drives.
1. HDD Drives
HDD is an acronym that stands for Hard Disk Drive. HDDs have been around for ages and their main characteristic is that they have moving/mechanical parts and also use magnetic storage technology.
For more than half a century, hard disk drives technology was the main storage media in computers. There has been an evolution in the HDD technology with time in terms of speed and size capacity.
For instance, hard disk drives made 50 years ago were larger in physical size, slower and had a much smaller capacity than the current ones.
Characteristics of a Hard Disk Drives:
Storage Capacity – Hard drives have varying storage capacities. The standard for measuring hard disk capacity is the byte. The storage capacity in modern hard drives is measured in gigabytes and terabytes. Up until 2018, the largest HDD available was 16 terabytes.
Speed – The access speed of hard disk drives is determined by how fast the magnetic plates’ data is read and written as the plates rotate. A standard HDD can read/write at speeds of around 125 Mbytes per second.
The type of connection also affects the speed and overall performance of hard drives. The revolutions per minute of mechanical hard drives also determine the speed.
For example, hard disks with an RPM of 7,200 are faster than those with an RPM of 5,400. However, HDDs are much slower than SSDs as we will see below.
Connection Type – Hard disk drives connect to a computer either via a SATA, parallel ATA (PATA), or a SCSI data cable. Older types used PATA but newer ones use SATA.
Cost – Magnetic hard drives are the cheapest among all other hard drives. Because of their cheap cost, they are now mostly used as backup systems whereby you don’t need to have fast read/write operations.
Physical Size – Magnetic hard drives are larger than solid-state drives because they have many mechanical components.
Durability – Hard disk drives are less durable because they have movable mechanical components and also their magnetic nature tends to deteriorate over time.
Energy Efficiency – HDDs consume a lot of energy (6-7) watts.
2. SSD Drives
SSD in full means Solid State Drive. As the name suggests, solid-state drives do not have any movable parts, unlike the traditional mechanical hard disks.
Instead, solid-state drives utilize flash memory technology. You can think of an SSD as an oversized memory stick because both use NAND technology for storage.
NAND involves saving collected data and information on microchips. NAND technology enables SSDs to save data and recall it even after switching off the disk.
Characteristics of a Solid-State Drive:
Storage Capacity – Solid state drives come in various sizes. The most common sizes for SSDs range from 128GB to 512GB. Up until 2018, the largest SSD available was at 100 TB!
Speed – SSDs are super fast. In fact, they are the fastest of any type of hard drive. Standard Solid-state drives boast speeds of over 550 MB per second. SSDs owe their prowess in performance to the fact that they do not have movable parts.
Cost – Solid-state drives are expensive. They cost more than a magnetic or a hybrid hard drive but their cost keeps getting lower over time.
Durability – SSDs are durable. Since solid-state drives – as the name suggests – do not have any moving parts, they are less susceptible to mechanical damage from shock or vibrations.
Energy Efficiency – SSDs consume less energy (2-3) wats compared to HDD.
3. Hybrid Drives (HDD + SSD)
Hybrid hard drives combine both hard disk drives and solid-state drives to use magnetic platters and flash memory.
In hybrid hard drives, the most commonly accessed data and information are stored in flash memory. The rest of the data is stored in the magnetic platters. The intention is to add speed to the already cost-effective and high capacity HDDs.
Characteristics of Hybrid Drives:
Storage Capacity – Hybrid hard drives come in smaller sizes, especially the SSD part.
Speed – Hybrid drives are fast. They are faster than magnetic hard drives because they use flash memory to access data quickly.
Cost – Hybrid hard drives cost more than magnetic hard drives but are cheaper than solid-state drives.
Computer Hard Drive Connection Interface Types
In this section we will discuss the various connection interface types that are used to attach hard drives to the rest of the computer system (usually to the motherboard of the computer).
The type of connection is crucial because it determines factors like speed, scalability, and compatibility. They include:
1. SATA Interface
Serial Advanced Technology Attachment, also known as Serial ATA cables (SATA), is replacing the older parallel ATA or PATA cables.
SATA cables joined the market in 2003 and have been replacing PATA cables ever since. Nowadays, many computers use SATA cables to connect hard drives and optical drives to the motherboard.
SATA uses serial signaling technology instead of parallel signaling, which is used by IDE hard disks.
Characteristics of SATA Interface:
Speed – The latest SATA models (SATA III) offer high read-write speeds of up to 600MBs per second of actual bandwidth or 6Gbps speed.
Energy efficiency – SATA interface uses little power.
Data integrity – SATA protocol facilitate data integrity by detecting and correcting errors.
Performance – SATA protocol can support a single command queue, each with 32 entries.
SATA cabling and connection is way simpler because SATA cables are more flexible and thinner.
SATA interfaces support more bandwidth than PATA protocols.
2. SAS (SCSI) Interface
SAS in full is Serial Attached SCSI (Small Computer System Interface). It is a point to point interface connection that uses a serial protocol. It replaces the parallel SCSI, which used a parallel bus.
Characteristics of SAS:
Speed – SAS protocols have been improving over the years. In 2017, the SAS-4, which boasts a data transfer rate of 22.5 GB per second, was released.
Performance – SAS can support only one queue and with 254 entries each.
Communication – Using expanders, SAS allows communication of up to 65,535 devices.
SAS gets rid of clock skew.
NVMe stands for Non-Volatile Memory Express. In comparison to legacy storage interfaces, NVMe offers higher scalability, performance, and optimization.
NVMe is the latest technology that uses PCI Express (PCIe) bus to connect the storage device directly to the CPU. NVMe was made for SSDs in order to provide the fastest interface communication of the SSD drive to the CPU.
Characteristics of NVMe:
Speed – NVMe is faster than SATA in all aspects. Whether its data access time, read-write speed, or input/output operations per second, NVMe will beat the quickest SATA model. For example, NVMe with SSD can offer throughputs of up to 32 Gigabytes per second.
Performance – NVMe can support up to 64,000 queues.
Digital storage and memory technology have evolved so much in the last half-century. This evolution has brought about increased data transfer rates and subsequently increased performance in both hard drives and their interfaces.
The reality is that storage devices are evolving, and traditional hard disk drives are slowly being phased out and will soon be completely replaced with the much faster SSDs connected with the latest NVMe interface technology.