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Computer Hard Drive Tutorial

Computer Hard DriveThis tutorial discusses the various types of hard drives and their features. Separate tutorials discuss installing hard drives and partitioning hard drives.

Every computer must have a hard disk drive (commonly called a hard drive, hard disk, or abbreviated HDD). Your operating system is stored on the hard drive. Of course any other file can be saved there too. It is the main location where people save data. Having adequate hard disk storage for your needs is important. The main purpose of this page explains the difference between a IDE and SATA hard drive, although a brief description of SCSI, solid state, and flash drives are discussed as well. But first I explain some common terminology.

Capacity is the maximum amount of data a drive or disk (for example, a DVD disk) can store. Typical hard disk storage capacities today are either in gigabytes or terabytes. These sizes store enormous amounts of data. This is very useful when saving music and video, especially video files, which can get very large.

RPM (Revolutions Per Minute) - Within a hard disk case are round platters (the actual disks) that are attached to a spindle that spins. The disks are written to or read from while spinning. One revolution is how many times the platters make a complete rotation. Disks in a HDD literally rotate thousands of times per minute. The greater the RPM, the faster data is read or written. 7200 RPM is typically what you will see in home computer hard drives.

Form Factor:
The form factor of a hard drive is the actual physical size of the case the platters are in. The main sizes are 3.5in and 2.5in.

Cache Memory:
A small amount of memory, usually 8, 16, or 32MB, is set aside for the most frequently accessed files. When one of these files is selected, it is retrieved from the cache. This reduces access time since the system does not have to search the drive for the data.

Types of Drives:
Now that the basics have been covered, let's look at some different kinds of drives. There are two main types used by home PCs and laptops: IDE/EIDE and Serial ATA (SATA).

IDE (Integrated Drive Electronics):
The IDE interface standard has been around for a very long time. The term interface in this sense means how the drive connects to the motherboard. As improvements were developed it later was called EIDE for Enhanced IDE. And after even further developments it has also come to be known as ATA (Advanced Technology Attachment). These drives connect to the motherboard via a flat, 80-wire cable to an IDE connector. Two drives can be attached on one cable.

Computer Hard Drive cable

The speed of a hard drive is determined by how fast the connector can send data. Currently the primary drive rates are 100 MB/s and 133 MB/s - 133 MB/s being the maximum. These hard disks are commonly described by the abbreviation "ATA" followed by the speed of its connector (ATA 100, ATA 133).

IDE drive connectors use a parallel bus, meaning multiple bits are transmitted simultaneously. To distinguish between Serial ATA drives, IDE disks are also referred to as PATA (the "P" stands for parallel).

Computer Hard Drive cable

To make it a little less confusing, here are some different names for IDE:
  • EIDE (Enhanced IDE)
  • ATA (Advanced Technology Attachment)
  • PATA (Parallel ATA)
Although there are still IDE drives around, Serial ATA is now the standard and is discussed next.

Serial ATA (SATA):
Today, SATA disk drives are the current standard and use a serial interface to transfer data, i.e. data is transmitted one bit at a time. Using a faster clock rate, sending one bit is faster than sending several with a slower clock, as with IDE. Data also travels along a single wire, reducing inteference. With SATA, one path is used for sending and another for receiving. With PATA, data is sent and received on one path.

The original SATA standard has a transfer rate of 150 MB/s (SATA-150). Now SATA can transmit up to 300 MB/s (SATA II or SATA-300), and 6 Gb/s (SATA 3), far surpassing PATA's 133 MB/s. SATA uses a 7-wire cable for connecting to the motherboard.

SATA hard drive

SCSI Drives:
SCSI (Pronounced "scuzzy") stands for Small Computer Systems Interface, and was originally developed to replace IDE before SATA came about. In addition to hard drives, other devices can use SCSI. Because PCs use either IDE or Serial ATA drives, I am not going to go into a lot of detail about SCSI, but I do want you to know that it exists and a PC is capable of using a SCSI drive if it has a SCSI controller.

SCSI is much faster than IDE. Several types developed over time: Narrow, Wide, Fast, Fast Wide, and Ultra. These refer to how much and how fast data is sent for each standard. The only one in use today is Ultra, itself consisting of various types. 8 or 16 devices are supported on one cable, depending on which kind is implemented. SCSI devices are a little more troublesome to configure than IDE and SATA and generally tend to be more expensive.

External Drives:
Hard disk drives can connect externally to a computer. The drive is placed in a case called an enclosure that contains a port(s) on the back for connecting to the computer via a cable. For quite some time enclosures used USB or Firewire. Now, many support any combination of USB, Firewire, and External SATA (eSATA) ports on the same encasement. External SATA is far faster than USB and Firewire. To use it, a computer must also have an eSATA connector. If it doesn't, a card can be purchased with the interface on it. Enclosures are manufactured to match the form factor of particular drive.

External hard drive

Solid State Drives:
Solid State Drives, or SSDs, differ from traditional hard drives in that they contain flash memory rather than a motor, spinning platters, and a read/write head. A big advantage is that you do not have to concern yourself with drive failure due to some mechanical failure, and they require much less power to run.

Like standard drives they come as internal or external, IDE or SATA. Most are 2.5 inches.

A big disadvantage with solid state hard drives, however, is capacity and cost. Presently, most come in much smaller capacities than regular drives and are quite expensive. So you will have to decide if the cost is worth it.

Flash Drives:
Flash Drives are portable drives about the size of your thumb that use flash memory to store data. They replaced floppy disks years ago as the primary method of transporting data from place to place. The early ones only had a capacity of 8 or 16 MB megabytes. Now, storage is in the gigabytes which allows you to store large files such as music and pictures. They connect using a USB interface.
Flash drive

Related Tutorials:
Installing Hard Drives
Partitioning Hard Drives

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