Performance with IDE Drives

Integrated Drive Electronics (IDE) drives are popular because the disk controller and drive are integrated into a single piece of hardware. This makes IDE drives less expensive than SCSI drives (which you will learn about in a later section in this chapter titled 'Performance with SCSI Drives'). IDE traditionally hasn't provided the same performance as SCSI-but even that has changed in recent years. New IDE standards, covered later in this section, are increasing IDE drive performance to be comparable to SCSI.

You can easily distinguish an IDE drive from a SCSI drive, because IDE uses a 40-pin connector whereas traditional SCSI uses a 50-pin connector. If you are using other forms of SCSI, wide SCSI uses a 68-pin connector and SCA SCSI uses an 80-pin connector.

master

A device that is responsible for controlling one or more directly connected devices.

slave

A device that is controlled by another device called the master.

You can connect IDE drives to the computer in two ways:

• You can attach them directly to the motherboard if the IDE adapter is integrated as part of the motherboard.

• You can attach them to a paddleboard. The paddleboard is not a controller. It is a simple piece of hardware that facilitates the connection between the drive and the motherboard. This hardware is inexpensive, usually costing under $20.

  

IDE technology enables you to install two drives per paddleboard. You designate one drive as the master drive and the second drive as a slave drive. Jumpers on the hard drive usually determine the drive designation. You should refer to the drive's documentation to see how to configure your particular drive.

jumpers

Plastic-covered metal clips that are used to connect two pins on a motherboard. The connection creates a circuit that turns the setting to 'on.'

Enhanced IDE (EIDE)

An extended version of the IDE standard. The benefits of EIDE include the support of hard drives over 528MB, the capability to chain devices other than drives (for example, CD-ROM drives and tape drives), faster access time, and the capability to chain up to four devices.

Note 

You can start, or boot, your computer only from the master drive.

Most IDE drives that are used today are actually Enhanced IDE (EIDE) drives. The original IDE specification supported drives only up to 528MB. EIDE supports drives in the 100's of GB range, and the maximum capacity is increasing with advances in technology.

Note 

In some hardware books and manuals, you will see references to RLL, MFM, and ESDI on the subject of hard drives. These standards have been obsolete for some time.

IDE Interface Standards

direct memory access (DMA)

A process wherein data moving between a device and RAM bypasses the CPU. The CPU is then free to complete other tasks.

IDE drives come in many formats, from 31⁄2-inch to 51⁄4-inch drives, with the former being the most popular today. But physical size doesn't matter much when what really counts is the speed and accuracy of the drive. Several standards have been developed to greatly improve IDE disk drive performance. These standards are actually protocols that the disk drive and the controller use to communicate with each another. Each protocol is made up of a set of rules that govern how communication will occur between the disk drive and the controller. Advancements in protocols can greatly improve hard disk performance. Faster communication between the hard disk and the rest of the computer means applications open more quickly and videos play more smoothly.

Several standards have been defined for IDE drives. As the standards have been released, they have typically doubled the amount of data that can be transferred. We explain each standard next.

Advanced Technology Attachment (ATA)

Advanced Technology Attachment (ATA) refers to a disk standard wherein the controller responsible for moving data on and off the disk is located in the drive. ATA is the original standard for IDE drives. ATA drives can have one or two drives connected to a single controller. As stated earlier, one of the attached drives is referred to as the master, and the second is the slave because of its dependency on the master. IDE drives slow the performance of the CPU because they must communicate directly with the CPU to access RAM. Some IDE/ATA drives have a transfer rate as high as 2MBps.

ATA-2

Someone referring to a computer with an IDE drive is more than likely talking about an Enhanced IDE drive based on the ATA-2 standard. ATA-2, or EIDE, made two significant gains over the original ATA standard. The first major advance was the capability to take advantage of the direct memory access (DMA) protocol. DMA improved CPU performance by accessing memory directly and avoiding the CPU whenever possible. The second enhancement was the capability of advanced BIOS to identify the type of hard drive from information on the drive itself, making installation much easier. ATA-2/ EIDE has a maximum transfer rate of 16.7MBps.

Ultra-ATA

Ultra-ATA drives, like ATA-2/EIDE drives, also make use of the DMA protocol. Ultra-ATA uses a faster mode of the DMA protocol (mode 3, to be exact), which pushes transfer rates to 33MBps. As with ATA-2/EIDE, your motherboard must support Ultra-ATA.

burst mode

The temporary increase in data transmission speeds beyond what is normal. The increase is not sustainable and usually prevents other devices from transmitting.

Ultra-ATA/66 and ATA/100

The ATA/66 and ATA/100 have been developed to complement today's larger applications and faster CPUs. With data transfer rates of 66MBps and 100MBps respectively, these two standards blur the lines between IDE and SCSI.

Note 

The Ultra-DMA/33 protocol was developed by Quantum Corporation to take advantage of faster Ultra-ATA disk drives. Ultra-DMA uses burst mode to temporarily take control of the bus to achieve data transfer rates of 33MBps.