Hard Drive Glossary

Hard Drive Glossary

Access is the action of obtaining data from or writing data into a data storage device.

American National Standards Institute.

Advanced Technology Attachment. ATA was originally defined as a standard for embedded fixed disk storage on IBM AT compatible PCs and is now the dominant storage interface.

Bit is an abbreviation for binary digit. A bit can only contain the value 1 or 0. The bit is the basic data unit for digital computers.

The buffer is the storage area used to temporarily store data so that a difference in data transfer rates and/or data processing rates between sender and receiver can be compensated.

A byte consists of eight bits.

Like the buffer, the cache is DRAM (dynamic random access memory) on the hard drive used to store temporary data that has recently been accessed or data waiting to be written to the disk.

Capacity is the amount of data that can be stored in a given storage device, usually expressed in bytes.

A channel (referring to that on a data cable) is a collection of electronic circuits used for data writing and reading processes to and from magnetic media.

Data is an ordered collection of information.

Gigabyte (GB)
A unit of storage. 1 GB can mean either 1,000,000,000 bytes using the decimal system or 1,073,741,824 bytes using the binary system. Most hard drive manufacturers define 1GB as 1,000,000,000 bytes, while the operating system will treat 1GB as 1,073,741,824 bytes. This is why the operating system shows the hard drive’s capacity as different to the manufacturer’s claim.

Jumpers are used to set a hard drive’s attributes, such as Master/Slave. A jumper is in essence a simple on/off switch and when placed over two pins it is the same as closing a circuit. The combination of one or several jumpers results in different settings.

Latency refers to the delay that occurs when requesting a specific response. Less latency is better.

Megabyte (MB)
A unit of storage. 1MB=1,000,000 bytes decimal or 1,048,576 bytes binary. Hard drive manufacturers usually apply the decimal system while the operation systems apply binary system of calculating storage capacity.

PATA (Parallel ATA), IDE/EIDE (Enhanced Integrated Drive Electronics)
ATA is the acronym for Advanced Technology Attachment, and it has become an industry standard hard drive interface for 15 years. ATA uses a 16-bit parallel connection to make the link between storage devices and motherboards, and is also called PATA to distinguish it from the newer SATA standard. In additional, ATA is also known as IDE or EIDE (Enhanced Integrated Drive Electronics). Currently the two most popular standards for ATA hard drives are the ATA-6 (which is also known as Ultra ATA 100 or Ultra DMA 100) and ATA 133. The maximum bandwidth for the former is 100MB/s, and 133 MB/s for the latter.

SATA (Serial ATA)
SATA is an interface standard for connecting hard drives to computer systems, and is based on serial signaling technology. The advantages over PATA include longer, thinner cables for more efficient airflow within a computer chassis, fewer pin conductors for reduced electromagnetic interference, and lower signal voltage to minimize noise margin. The bandwidth of SATA is also far improved over today’s PATA – the SATA 1.0 can reach a maximum of 1.5Gb/s (150MB/s), while the latest SATA 2.5 standard can support up to 3Gb/s (300MB/s). As a result of so many advantages, the SATA interface is gradually replacing PATA as the mainstream hard drive interface in the personal storage market.

SCSI (Small Computer System Interface)
SCSI is a standard interface for transferring data between devices and computers. Thanks to its outstanding ability to compartmentalize diverse operation, SCSI is very suitable for multitasking operating environments. Also, SCSI enhances critical performance in situations where more than one device is connected. 

Before serial signaling technology was applied into the SCSI field, all SCSI interface standards used parallel technology to transfer data.

RAID (Redundant Array of Independent/Inexpensive Disks)
RAID is a method of using multiple hard drives together for data storage. A RAID system with multiple hard drives appears as a single drive to the operating system. Depending on the RAID level, the benefits provided by RAID is one or more of the following: better throughput, fault-tolerance or capacity (or something else) when compared to single hard drive.

1. RAID level 0 (or RAID 0) is known as striping, where data is striped across multiple hard drives. RAID 0 provides the most advanced throughput and capacity, but offers no fault-tolerance.
2. RAID level 1 (RAID 1) is known as mirroring, which stores the exact same data within at least two hard drives, this method shows excellent fault-tolerance and reliability, but delivers less capacity efficiency.
3. RAID level 0+1 and RAID 1+0 are both striping and mirroring, providing good fault-tolerance and throughput all at the same time. There are other RAID levels available too, such as RAID level 5 and RAID level 6.

Reading is the action of access a storage location and obtaining the stored data.

Writing is the action of recording data on a storage device.