Hard Disk Drives
There are numerous types of drives used for storing computer data; these include floppy drives, hard drives, CD-ROM drives and so on. These drives use differing types of technologies to store information, including magnetic and optical storage. Modern hard disks consist of one or more magnetic disks contained in a box that is typically 3.5 inches in diameter. Size and speed of the hard drive are decisive factors in a computer's performance.
A disk drive is made up of a disk that stores information, a motor that rotates the disk, a magnet, and an actuator with read/write heads attached to suspension arms that magnetically and electronically read and write information on the disk surface.
When the motor is powered up the disk rotates and causes the read/write heads to fly above the disk surface on a cushion of air. They are two or three microns above the surface, and the disk can rotate up to 7200 RPM or more, which means that the heads can be travelling at speeds in excess of 64 miles per hour. Under normal operation there is never any head to disk contact.
Hard Disk
Magnetic Disk
EIDE Cable
IDE Sockets
EIDE
Hard drives can be distinguished by their interface types. Today's systems generally have either EIDE controllers or SCSI controllers. EIDE (Enhanced Integrated Device Electronics) is the current standard for inexpensive, high performance hard disks. It is the enhanced version of the old IDE standard. EIDE controllers are integrated onto motherboards. The acronym ATA (Advanced Technology Attachment) is synonymous with EIDE. Most modern BIOS software can autodetect an EIDE disk, allowing it to work immediately once it is installed.
The hard disk is connected to the motherboard by means of an EIDE signal cable. Each motherboard has sockets for two EIDE cables (a primary channel and a secondary channel), and has connectors for two units (a master and a slave) on each channel.
The EIDE interface is designed for more than just hard disks. It can be used for a variety of devices, including CD-ROM drives, CR-RW drives, DVD drives and other types of storage media. A new PC will usually have two EIDE units connected, a hard disk on the primary master, and a CD-ROM drive on the secondary master. A second hard drive must be placed on the primary EIDE channel's slave connector. Additionally, you also must set jumpers on the disk drive itself to specify if it is to be a master or slave disk. Jumper pins are used to detail the jumper setting that specifies how the drive is to be used.
A typical setup with four EIDE devices might look like this:
Primary master = Hard disk 1
Primary slave = CD-ROM
Secondary master = Hard disk 2
Secondary slave = LS120 diskette
As shown, on an EIDE host controller there are sockets for two EIDE cables. For a system with a single hard disk, it should be assigned as primary on the master channel. In general, to achieve optimal performance, if you have two hard disk drives, each should be assigned as masters on the primary and secondary channels.
This is because the slave and master sub-channels on a given channel can not multi-task; only one operation is performed at a time, as opposed to the primary and secondary channels, which are capable of multitasking.
EIDE Controller
Juggling four (or more!) EIDE units on a system can be a difficult task.
One possible solution is to expand your system's EIDE capabilities with a PCI-based EIDE controller. These expansion cards work side-by-side with your existing EIDE controller and can be connected to additional hard disks, CD-ROMs, ZIP or other ATA-based drives.
SCSI
The SCSI (Small Computer System Interface) interface is typically found in high end systems and servers. The main difference between SCSI and EIDE is that a single SCSI adapter can handle 7 or 15 devices, of varying types (internal or external hard disks, scanners, CD-ROMs, zip drives, etc.). Another difference is that while most modern systems have their EIDE controller as part of the motherboard, SCSI controllers are often a separate expansion card. SCSI drives are faster and generally more robust than EIDE drives. The SCSI system holds its own computer power, thus freeing the CPU.
Hard Disk Upgrades
Hard disks have become progressively faster and cheaper, and with their increased capacity can hold ever-growing amounts of data. Upgrading your hard disk is a common improvement you can make to your system, as is adding a second hard disk. However, as drives get faster, they require improved cooling. Many modern systems now come with multiple cooling fans to stop drives from overheating. It is important to keep your system's cooling fans clean and dust-free, and to make sure they are running properly. Keep a new hard disk in its electrostatic discharge protection container until you are ready to install it. Handle hard disks carefully, and never handle more than one at a time. Never stack them or place them on edge. Avoid dropping a drive -- even a 1/4 inch drop can cause damage.
Before you can physically install a new hard disk into your computer you must make sure that it is configured properly. For an IDE drive this means specifying (using jumpers) whether it is a master or a slave device.
There is no standard way to set jumper pins. It varies across manufacturers, and even across different drives from a single manufacturer. Consult your drive's documentation, or the manufacturer's web site for jumper setting configuration. Many drives have the proper jumper settings printed directly on the drive itself.
For a SCSI drive, configuration entails setting the device's SCSI ID and the SCSI bus termination state.
Each device on the SCSI chain must have a unique SCSI ID. On most systems the SCSI controller is set as the highest available ID (ID 7 on non-wide systems and ID 14 on wide and ultra-wide systems). Typically the boot drive is set as 0. Some SCSI controllers allow you to skip IDs (for example, you can have ID 0, ID 1 and ID 3), other controllers do not permit this.
If you are installing a new SCSI drive in a system that has other SCSI devices installed (for example, a scanner or a tape backup unit), terminate only the end devices on the SCSI chain.
Use all four screws to securely mount your drive. Using less than four screws may be tempting, but it may cause the drive to vibrate excessively, and this can shorten its life. Do not tighten the screws, however, as this can warp the drive's internal frame.
After physically installing the drive you will need to configure it. First, you will need to run FDISK in order to partition it, thereby defining areas of the disk for an operating system to use as a volume. FDISK writes a master partition boot sector on the first sector of the hard disk. This partitioning also prepares the drive for formatting, and tells the ROM BIOS which of the partitions are bootable. If you are unfamiliar with FDISK, we encourage you to read Using the FDISK Utility.
Second, you will need to format your disk. There are two format procedures that are required prior to your using a new hard disk:
Low-level or physical formatting (LLF)
High-level or logical formatting (HLF)
When you format a floppy diskette, both types of formatting are done simultaneously, but on a hard disk they are separate procedures. The LLF is performed by the manufacturer prior to sale, and for EIDE drives this is usually never done by the end user. The low-level format writes the tracks and sectors on the disk.
The HLF is what is done by the DOS FORMAT command. If you are unfamiliar with the DOS FORMAT command, we encourage you to read Using DOS FORMAT. During the high-level format the operating system writes the structures required for managing data on the disk, basically creating a table of contents. Hard Drive Problems
Your computer's hard drive holds your data, and so is an extremely important and valuable part of your computer. Many things can go wrong with a hard drive -- some catastrophic, like total failure of the media (which can prevent your system from starting), while others are not catastrophic, but still serious, like sectors going bad (which can lead to the loss of a file or files). For many of these problems the troubleshooting activities vary only slightly, depending on, for example, if your drive is receiving power or not.
Warning: Anytime you do hard drive troubleshooting you take the risk of destroying any data on the drive. It is always wise to attempt to backup any data prior to troubleshooting, if possible. Never reformat or partition a hard drive except when all else fails, and always do regular backups of your data.
If you do not see any drive light or hear any drive activity and you see a message that the drive cannot be located:
Try booting from a boot diskette. If you can, then the problem is with your hard drive.
Try switching to the C: drive. If you can access it, you may have a boot sector problem. You should check for a boot sector virus immediately. If you can not access the drive, continue troubleshooting.
Make sure the 4-pin power connector is inserted securely into your drive. If your drive is on a Y-connector make sure any other connections are secure.
Make sure the signal cable from the motherboard to the hard drive is securely seated. Check for frayed edges or other damage to the cable. If you have a spare, try replacing it. If it is an EIDE cable, make sure that the red stripe that you see on one side of the cable is aligned properly with pin 1 on the disk. Enter your CMOS Setup and confirm that the parameters for your hard drive (heads, cylinders, sectors per track, etc.) have been entered correctly. In most modern systems these parameters are automatically detected, but you need to make sure that the drive is enabled in the CMOS Setup.
If you have a separate drive controller board (most modern systems do not unless they are SCSI systems) make sure it is seated securely in its expansion slot.
Try switching the non-working drive with a known, good, drive (remember you may need to change the CMOS Setup settings if you do this). If the good drive works as you expected, then the replaced drive is bad. If it does not work as expected, you may need to replace the disk controller or the motherboard.
If you see or hear drive activity (constant or intermittent) but your boot drive can not be located (you might see a "No Fixed Disk Present" error message on the monitor):
Check to make sure the signal cable is inserted with the proper orientation (that it is not reversed at one of the two ends).
Check that the signal cable is in good condition.
Check that your CMOS Setup has the correct parameters for the drive. In most modern systems these parameters are automatically detected, but you need to make sure that the drive is enabled in Setup.
Boot from a boot floppy and attempt to access the drive. If you can, it is likely that your boot files have become corrupt. Check for boot sector viruses immediately.
Try switching the non-working drive with a known, good, drive (remember to change the CMOS Setup settings if you do this). If the good drive works as you expected, then the replaced drive is bad. If it does not work as expected, you may need to replace the controller board.
If you hear your disk spinning up but it is not recognized by your computer (you may get a "Hard-disk error" or "Hard-disk controller failure" message on your monitor):
Check to make sure the signal cable is inserted with the proper orientation (that it is not reversed at one of the two ends).
Check that the signal cable is in good condition
Check that the jumpers are set correctly on your drive(s) and that the primary is set as primary, and the secondary or slave, if existent, is set as secondary.
Check that your CMOS Setup has the correct parameters for the drive. In most modern systems these parameters are automatically detected, but you need to make sure that the drive is enabled in Setup.
Boot from a boot floppy and run FDISK to confirm that there is at least one DOS partition and that if it is your boot drive, that it is active and bootable.
Boot from a boot floppy and attempt to access the drive. If you can, it is likely that your boot files have become corrupt. Check for boot sector viruses immediately.
Try switching the non-working drive with a known, good, drive (remember to change the CMOS Setup settings if you do this). If the good drive works as you expected, then the replaced drive is bad. If it does not work as expected, you may need to replace the disk controller or the motherboard.
If you hear your drive spinning up at start-up but then it immediately spins down:
Check to make sure the signal cable is inserted with the proper orientation (that it is not reversed at one of the two ends).
Check that the signal cable is in good condition.
Check that the jumpers are set correctly on your drive(s) and that the primary drive is set as master, and the secondary or slave, if existent, is set as slave.
Try switching the non-working drive with a known, good, drive (remember to change the CMOS Setup settings if you do this). If the good drive works as you expected, then the replaced drive is bad. If it does not work as expected, you may need to replace the disk controller or the motherboard.
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