What is a hard drive?
A hard drive is one of the key components of a modern computer. The hard drive is where all of your programs and files are stored.
How does a hard drive work?
A traditional hard drive uses similar technology to cassette and VHS to store your data. Inside the hard drive there are several delicate metallic platters. Just as a head inside of a cassette or VHS player reads the data on a tape there is a head inside of the hard drive that moves over the platters reading and writing data.
When you turn on your computer the platters immediately begin to spin up to speed. The platters in a modern hard drive will spin between 5400rpm and 7200rpm, you may be able to hear a slight hum from your PC when your fan is not running and this will be the sound of your hard drive.
When your computer is on but you are not accessing the drive the platters will continue to spin. The arm with the heads on it (called the actuator) will only move when you read or write data to the drive.
What is Average Seek Time?
In order to read or write data in a particular place on the disk, the actuator arm with the read/write head of the disk needs to be moved into the correct place. This process is known as seeking and the time it takes a drive to get the head into the correct place is the seek time.
Seek time can vary depending on the starting point on a drive, the head may have to move 10% across the platter or 80% across the surface of the platter and both will give different seek times. This is why the measurement is taken as an average seek time to allow for comparisons to be made between drives.
Solid State Drives (SSDs) do not have what we normally define as seek time because they do not feature any moving parts. There is however a delay from the hardware signal from the other components in the system which is described as seek time normally of 0.1ms or below.
What does RPM stand for?
RPM stands for Revolutions per Minute.
RPM is a measurement of how many complete revolutions the platters in a hard disk drive make in a single minute. The general rule is the higher the RPM the faster the data on a hard drive will be accessed and transferred.
The standard speeds you will find listed among modern hard drives are as follows:
5400RPM: Typical speed used on laptop hard drives and value multi-purpose or storage drives.
7200RPM: Used primarily on multi-purpose drives and offers a good balance between performance, noise, heat and cost.
10,000RPM: Ultra-performance speed for mechanical hard drives found in desktops. Offers the highest levels of performance currently available from desktop mechanical hard drives. The performance offered by this class of drive have been replaced by the Solid State Disk technology which offers higher levels of performance without the high levels of noise and heat these hard disk drives can output.
3200RPM-7200RPM: Variable rotational speeds are often used in dedicated storage drives such as the Western Digital Caviar Green range of drives. The hard drive can increase or decrease its spin speed to save energy or offer increased performance on demand. These drives are ideally used as a secondary hard drive with a Solid State Disk having the operating system installed on it.
What are the physical sizes of hard drives?
Hard drives are available in two major form factors, 2.5” and 3.25”. The standard size of drives for use in laptop computers is 2.5” while desktop hard drives are usually the 3.25” form factor.
Solid state hard drives are normally made using the 2.5” form factor and may need an adapter to be installed securely into a standard desktop case.
What interfaces are there for hard drives?
There are many ways of connecting a hard drive to your PC, primarily you have internal and external connections depending on how you wish to connect the drive.
USB: Probably the most well known form of computer connection. USB stands for Universal Serial Bus and was designed to replace many varieties of serial and parallel ports. USB can connect computer peripherals such as mice, keyboards, digital cameras, printers, MP3 players and flash drives. For many devices USB has become the standard connection method although it is only one of many for the hard disk drive due to performance limitations.
There are three versions of USB currently used by external hard drives, each varying in performance.
USB 1.1: Offers speeds of up to 12Mbit/s and should be avoided by modern systems.
USB 2.0: Offers speeds of up to 480Mbit/s and is the most common of the external hard drive connections. Has enough performance to be useable on a day to day basis although a hard drive on the USB 2.0 is noticeably slower than a comparable drive running on the IDE or SATA internal interfaces.
USB 3.0: The latest and fastest USB standard offering speeds of up to 5120Mbit/s and offer comparable performance currently to the internal standards.
USB drives ensure the highest levels of compatibility with computers and a comparatively low cost to some of the competing standards making them the default choice for people wishing to share the same hard drive around multiple computers.
Firewire: Sometimes known by its technical name IEEE 1394 is another popular standard for connecting high performance devices to a computer. Originally pioneered by Apple for use on their range of Mac products the Firewire interface soon became popular in the PC world thanks to its high levels of performance.
Firewire was originally designed as a high bandwidth connector which could effectively connect devices such as hard drives, audio interfaces and video equipment to a computer. It offered performance over 10x that of USB at its introduction.
Firewire hard drives offer performance equal to or better than the same drive on the USB 2.0 connection. The latest versions of Firewire rival the performance offered by USB 3.0.
Firewire has become the standard connection for professionals who need external storage on a single PC. Although Firewire drives can be used on any PC with a Firewire interface due to them being less common than USB connectors many users favour USB based hard drives for mobile use.
eSATA: The eSATA connector is a more robust SATA connector, intended for connection to external hard drives and SSDs. It has a far higher transfer rate (3Gbps, bi-directional) than USB 2.0. A device connected by eSATA appears as an ordinary SATA device, giving both full performance and full compatibility associated with internal drives.
eSATA does not supply power to external devices. This may seem as a disadvantage compared to USB, but in fact USB's 2.5W is usually insufficient to power external hard drives. eSATAp (power over eSATA) is a new standard that supplies sufficient power to attached devices using a new, backwards-compatible, connector.
eSATA is rare even on modern systems although when it is present it offers the highest levels of performance of any of the external connections.
What types of hard drive are there?
Modern hard drives can be categorised into several different groups, each of them specialised for one particular use. The major groups for hard drives are SSD (Solid State Drive), Storage Drive and the multi-purpose drive. With very few exceptions external drives fall under the Storage Drive category.
SSD Drives: A solid-state disk or drive (SSD), sometimes called a flash drive, is the next generation hard disk. Though the architecture of an SSD does not employ disks at all, the name is carried over from standard hard disks. In reality a SSD utilizes a special kind of memory chip with erasable, writeable cells that can hold data even when powered off.
An SSD has many advantages over a traditional drive. Seek time is decreased significantly, making the SSD very fast not only in benchmarks but in general use. A PC with a SSD drive installed will “feel” more responsive to the user in operation over a conventional hard drive. Being sold-state, the drive has no moving parts to malfunction, and does not generate significant heat. It is also lighter than a standard drive, more power efficient, and completely silent. Finally, the SSD is more durable. If dropped or banged it isn’t as likely to be damaged.
It is widely regarded that upgrading a modern PC or laptop with a Solid State Drive is the most worthwhile performance upgrade you can make. With a laptop thanks to the reduced power consumption of a Solid State Drive battery life can also be increased.
Storage Drive: A storage hard drive generally offers massive amounts of storage with low power consumption compared with normal drives. All the manufacturers now offer a range of storage drives with technologies in place to keep operational and environmental costs down. For example the Western Digital Caviar Green series of drives feature the following range of technologies:
- IntelliPower – A fine tuned balance of spin speed, transfer rate and caching algorithms designed to deliver both significant power savings and solid performance. Additionally the Western Digital Caviar Green hard drives consume less current during startup allowing lower power loads on systems as they are booted.
- IntelliSeek – Calculates optimum seek speeds (how fast the actuator arm and head are moving over the platters) to lower power consumption, noise and vibration.
When combined these technologies make for a drive that offers comparable transfer speeds to that of a standard multi-purpose hard drive but with slower access times. Power consumption can be reduced by up to 45% compared to a standard hard drive while operating temperatures, noise and vibrations are all decreased.
Storage drives are best used as the second hard drive in a system with a SSD as the drive with the operating system installed on. This allows the secondary drive to power down when not needed giving even greater power savings. The performance limitations of storage hard drives are mainly removed when the operating system is installed on another drive. Normally the Eco/Green storage drives in a manufacturer’s range are priced very aggressively and offer the best value for money per Gigabyte that you purchase.
Multi-Purpose Drive: The traditional mechanical hard drive. Offers good performance compared to other mechanical drives but is still considerably slower than a SSD drive, the benefit being a higher capacity for less money.
The energy saving features used on the storage hard drives may or may not feature fully on these models. Performance is usually favoured over any potential energy savings.
Generally systems with a multi-purpose hard drive will only feature a single drive that holds both the operating system and the user’s data.
The use of a single multi-purpose drive is the industry standard for low to mid-range systems although at the high end the emergence of SSD drives is slowly taking over.