IDE Devices in Brief

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There are typically two types of hard disk drives supported on the personal computers: IDE and SCSI .^[*] In a typical configuration, a PC motherboard would have two IDE controllers supported, each of the controllers in turn supporting two IDE devices. For the sake of simplicity, the SCSI controllers and drives are not addressed in the current discussion. Also the default configuration sold by most of the vendors through stores as well as mail orders have IDE controllers and not SCSI controllers. Examples of IDE devices are hard disk drives, CD-ROM, CD-R, CD-RW, DVD-R, internal zip drive, and so on. One IDE controller is identified as primary and the other as secondary. The motherboard manual of the computer can help identify these controllers. Again, each of the controllers identifies the two IDE drives as master and slave, respectively. Thus, at a maximum, a typical PC can have four IDE drives identified as primary master, primary slave, secondary master, and secondary slave. However, recent technological advancement enables you to add more IDE controllers through PCI cards attached to the PCI slots. One such PCI card gives you two additional IDE controllers, thus enabling you to connect four more IDE drives. The master-slave relationship of IDE devices is set by jumper settings on the specific IDE devices. One such setting is known as Cable Select, which means that the particular IDE device having this setting lets the IDE cable decide whether the device should be identified as master or as slave in the master-slave duo configuration. An IDE cable contains three connection points—the two ends and a center connection point. Although one end of the cable is marked to be inserted into the IDE controller (primary or secondary controller located on the system main-board, or the additional IDE controller located on the controller card added as a PCI device), the other two connection points (located at the center and the other end of the cable) are marked to connect to the primary IDE device or secondary IDE device. If the jumper setting on the IDE device is made to Cable Select, then the appropriate connection point on the cable should be used to connect to the device. It is also possible to manually set the master-slave relationship on the IDE devices, and more details on how to connect IDE devices to the IDE cable in a PC may be obtained by referring to the device vendor’s manual.

Even though the personal computer can have a number of drives, the primary master drive must be a hard disk drive, from which the computer boots. The motherboard of the computer is also equipped with the ROM BIOS (also called CMOS ROM), which stores the initial startup configuration information set by the motherboard vendor. The BIOS configuration may be accessed by invoking the BIOS setup program, by pressing a key sequence while booting the computer. The key sequence is specific to the motherboard, and the motherboard manual is the correct help source for more information. On most computers, a message is also displayed with the key sequence information in the beginning of the boot process. For example, it may be the F2 key, or the DEL key, the CTRL+ALT+S key combination or CTRL+ALT+ESC key combination, and so on. Most of the time, you do not have to do anything with the BIOS setup. But, if you add a new hard drive—or for that matter any new IDE drive—and if the BIOS does not recognize it automatically, you may have to enter its parameters (such as the number of cylinders, heads and sectors, and so on) in the BIOS setup. Also, when you are installing an operating system and you want the system to boot from the CD-ROM without attempting to boot from the hard disk, then you will have to change the booting sequence, which was already set in the BIOS. The default booting sequence may be different on different motherboards. The booting sequence tells the computer which devices should be checked for a valid operating system image to start the booting process. A typical booting sequence may look like Floppy, CD-ROM, HardDisk, which means that the computer first looks for a bootable floppy in the floppy drive. If it does not find one, it looks for a bootable CD-ROM in the CD-ROM drive, and if it does not find one, then it looks for an IDE hard drive, which is identified as primary master. It is strongly recommended that the BIOS setup should be accessed with caution, as you may make changes that would have an impact on the booting process. One who is thorough and knowledgeable with the BIOS setup configuration values can play with different setup configurations. Even if the computer fails to boot, the BIOS setup should be available for access without any difficulty. Sometimes the motherboard vendors may also provide upgraded BIOS when they add additional configuration options to the BIOS.

^[*] IDE stands for Integrated Drive Electronics. SCSI stands for small Computer systems Interface and should be pronounced "skuzzy." The SCSI devices are expected to give better performance over the IDE devices. However, the SCSI devices are substantially expensive compared to the IDE devices, and therefore the IDE devices have almost been the defacto standard followed by most of the personal computer manufactures. The IDE abd SCSI are two different types of drive interface architectures, and drives designed for one type of architecture cannot be used to connect to contollers of the othertype, with their standard design. There are hardware converters available in the market that claim to convert the IDE devices to be connected to the SCSI controllers, thus boosting the performanceof the IDE devices with minimum investment.

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