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EIDE (Enhanced IDE) Interface

The majorty of hard drives are EIDE drives. EIDE is used with other devices as well, such as CD and DVD drives, zip drives and tape drives.

ANSI Standards for IDE Drives:

IDE/ATA
First standard for IDE drives. Limited to no more than 528 MB and supports PIO and DMA transfer modes. Speeds range from 2.1 MB per second to 8.3 MB per second.

ATA-2/Fast ATA
Allows for drives larger than 528 MB and up to four IDE devices. Supports PIO and DMA transfer modes. Speeds up to 16.6 MB per second.

ATA-3
Improved version of ATA-2 with about the same performance.

Ultra ATA/Fast ATA-2/Ultra DMA/DMA 33
Improved DMA mode transfer rates with performance up to 33.3 MB per second.

Ultra ATA 66/Ultra DMA 66
Uses 80 wire IDE cable with extra grounding to improve signal strength. Speeds up to 66.6 MB per second.

Ultra ATA 100
Speeds up to 100 MB per second.

Ultra ATA 133
Speeds up to 133MB per second.

SATA (Serial ATA)
Speeds up to 300MB per second. Uses smaller cable than PATA IDE drives and only allows for one device per cable.

Transfer Modes

A hard drive can use one of two transfer modes. They are DMA and PIO. DMA transfers data from the hard drive to memory without involving the CPU. PIO mode includes the CPU in the process which makes it slower than DMA.

IDE Cables

Current IDE hard drives use two types of cabling. They are PATA (Parallel ATA) and SATA (Serial ATA).

PATA

A PATA cable is an 80 wire IDE cable used by ATA/66 and higher hard drives. Forty of the wires in a PATA cable are ground wires used to reduce crosstalk. These ground wires alternate in between the signal wires. These cables are also known as ATA/100 cables or Ultra DMA 100/66 cables. Standards before ATA 66 used a regular 40 wire. The only difference between the 80 wire and 40 are the ground wires. They look the same, other than one having twice as many wires, and an 80 wire cable can be used in place of a 40 wire IDE cable. The maximum lengh of a PATA cable is 18 inches.

SATA

A SATA cable is much thinner than a parallel IDE cable and has few wires (minimum of 4). The maximum lengh of a PATA cable is 1 meter. SATA hard drives are faster and are currently on their way to replacing PATA drives. SATA is designed for larger drives with higher performance than PATA hard drives.

EIDE Hard Drive Configurations

Most motherboards by defualt can support up to four IDE devices in a single PC. The motherboard offers a primary and secondary IDE channel. Each channel can support one IDE cable with two devices running off the same cable. One of the devices is configured to act as the master and the other as the slave. These configuartions are configured using either jumpers or DIP switches.

Primary channel, master device
Primary channel, slave device
Secondary channel, master device
Secondary channel, slave device

Most motherboards that support serial ATA have two SATA connectors. A single serial cable only supports one device. In a standard setup you can have up to four PATA and two SATA devices.

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