How Hard Disk Drives Work In Personal Computers

Introductions And Overviews

This guide provides insight into what the hard disk drive is and how it operates. It also provides background information into how the hard drive has changed extraordinarily throughout the past few decades.

The fundamental purpose of any storage medium inside a personal computer is to keep data secure and files intact when there's no power running through the machine.

A hard drive consists of a number of integral components all precisely manufactured within a small three dimensional rectangular box comprised of a metal aluminum material. No bigger than six inches long, four inches wide, and three inches high, this complex box can house a large quantity of binary data. The amount of data it can actually store varies depending on the specifications of the drive. A hard drive with a forty gigabyte (GB) capacity is capable of storing rougly forty billion bytes of data.

Some hard drives (such as the ones manufactured with serial ATA (SATA) connectors or Small Computer System Interface (SCSI) components are equipped with better specifications and larger capacities best suited for server computers. Other hard drives are best suited for desktop workstations when they are just above what the end-user actually needs or wants. Whatever the amount of choices available to end-users, the hard drive will remain the best method for the mass storage and retrieval operations of data. And with prices of hard disk drives falling just under $0.50 per gigabyte adding a supplemental disk for extra storage is a very inexpensive upgrade.

Choosing a File System

There are three file systems recognized by the Windows family of operating systems. They are NTFS, FAT, and FAT32. This article provides a comparison look into the advantages and disavantage of each major file system complete with suggestions on how to choose an appropriate file system based on how you use a computer.

While NTFS is the most secure of the three systems, FAT and FAT32 offer a more compatible format of storing and retrieving files and these systems are best suited for use on a Windows ME or earlier based PC. NTFS is more secure than FAT or FAT32 and as such requires a fair bit of knowledge during the administration or transferring of files through a network. NTFS file systems are strongly recommended for systems running Windows 2000 Professional, Windows XP Home and Professional, and the Windows Server family of operating systems. FAT and FAT32 file systems are also ideal for users running a dual-boot configuration (such as running Windows XP Professional and Windows 98/ME) on the same system.

It is also important to note that if you run a server based operating system such as Windows Server 2003 or Windows Advanced Server 2000, NTFS is the only file system recognized by Active Directory and domain based security systems.

The Importance Of Hard Disk Drive Backups

It is necessary for PC users and large corporations to back up their data on a daily basis. As data is crucial to any PC user or large corporation, it is recommended for data to be backed up periodically, allowing for an easy restoration of the data in case of any hard drive failures.. Power surges can quickly erase data from a hard disk drive, so backing up the data on a hard disk is strongly encouraged. This section will outline the various steps a user would take in making a proper backup of their data.

1. The first step in backing up data on a hard disk drive, is selecting the appropriate mass storage device to back the data up on. Floppy drives, are typically inadequate for this procedure as they do not have the capacity to back up data on more modern drives. It would probably take at least 40 or 50 3.5" floppy disks and hours of time to back up 500 MB of data (refer back to the section on the capacities of floppy diskettes in Chapter three.) However, on older drives, such as those being run on a 486 or earlier machines, you may be able to get away with using floppy drives to backup your data.
   
   
2. Common mass storage devices include CD-R Drives, CD-Re-writeable Drives, and Tape Drives such as Iomega's 100MB Zip drive. This devices provide the easiest and quickest method for backing up your data.
   
   
3. The next step in the backup procedure is choosing a software package to back up your hard drive. You could possibly back up your data manually (meaning copying each file or subdirectory on the drive to the storage medium) but this is a tedious procedure and can be easily simplified through the use of back up software. Microsoft Windows 95 comes with a utility called Backup, available in the system tools folder in the accessories folder on the start menu if you are running Windows 95. Backup allows you to choose a method of backup, either selecting each file or subdirectory individually, or choosing the a letter representing the drive you wish to back up.
   
   
4. Once you've obtained and decided which software you want to back up your hard drive with, the next obvious step would be to start the back up procedure. Depending on the size of your hard drive, the time it takes for this process to complete will vary.
   
   
5. One general note about backing up data is that it should be done periodically. It is recommended by most PC specialists that a backup should occur at least once per month, that way you can assure your data is kept current.
   

How Internal Drives Connect

There are four channels on an EIDE drive with each channel supporting two devices in a master/slave configuration. There are four connections utilized by the EIDE interface. The following table summarizes these connections and lists the typical device attached to these connections.

1. Primary Master Hard disk drive # 1 - Typically the primary boot up drive.
2. Primary Slave Primarily used as a CD-Rom drive. The secondary master can also be configured as a second or third hard disk drive in the system.
3. Secondary Master Hard disk drive # 2 - Typically a secondary boot up drive or storage drive.
4. Secondary Slave Used as a tape drive, or any other backup drive such as an Iomega Zip or Ditto drive. A 120MB super floppy can also be configured as the secondary slave or boot up drive

The primary master is typically reserved for the hard disk drive you are booting from, but on newer systems, these settings can be changed to reflect a CD-Rom or tape drive as the primary master. You may want to use a tape drive as the primary master, if you are experience problems with your system or you suspect your hard drive is failing and don't wish to boot up using the hard disk.

Transfer Protocols Associated With EIDE:

There are several transfer protocols associated with an EIDE interface. They are: primary and secondary EIDE, Ultra DMA (ATA-33), and Ultra DMA (ATA-66). The fastest transfer protocol by far is the Ultra DMA (ATA-66) capable of theoretically transferring data at speeds of up to 66 MB/second. The slowest of all protocols is the primary EIDE protocol which transfers data at a maximum theoretical speed of 13 MB/second.

In the OSR2 version of Windows 95, Ultra DMA requires the drivers to be installed correctly. Ultra DMA is completely supported under the Windows 98 operating system,
Requirements for the UDMA Transfer Protocol:

There are certain requirements that a system needs to meet to ensure the Ultra DMA interface is running properly. They are as follows:

   1. The hard disk must be the Ultra DMA type.
   2. The system board must have a chip set, which supports Ultra DMA, such as 82430TX or 82440LX.
   3. BIOS must "log on" the hard disk with Ultra DMA protocol. You can verify that in the start up screen.
   4. Drivers for the chip set must be installed in Windows 95.

SCSI Identification

SCSI Chain Of Command Identification System

To ensure that two SCSI devices are not using the same identification number, all SCSI devices, require a unique address (always labeled ID0 through ID7). The typical SCSI2 system can handle 8 devices and the SCSI Wide system handles 15 devices. SCSI devices can be internal or external, as a SCSI system always has at least one external connector on the controller itself. The typical SCSI chain is shown to the right. As already noted, each SCSI device within the system must have a different SCSI address, meaning that 2 SCSI devices cannot share a SCSI ID # such as SCSI-ID 2. A jumper or dip switch is typically used on the device itself to change its identification number. One final thing to remember about SCSI devices, is that the hard drive typically always occupies ID # 0 on the SCSI chain.

Overview Of Logical Block Addressing

LBA or Logical Block Addressing rearranges the apparent geometry of a hard disk. LBA is a way of addressing hard drives by assigning numbers sequentially to each sector on a hard drive. The only way LBA can be efficient is if it is used by the operating system and applications on the software side of the BIOS. LBA can be a more efficient method to handle files on drives larger then 528 MB but LBA does not necessarily improve system performance.

SCSI drives always employ LBA, and it is just recently that IDE drives started to use LBA. To implement LBA, both the hard drive and the BIOS, must be aware that the hard drive is in LBA mode and the drive itself must support logical block addressing. On most hard drives, the use of LBA is not required as it; what is required to support a large hard drive is a translating BIOS.

Most drives that support LBA do not require that LBA is used and LBA addressing is not normally required in order for a BIOS to support large drives. What is required to support large drives is a translating BIOS.

Comparison Between Old School And New School Hard Disk Drives

This document is intended to give you a brief comparison between the Pentium and the 486 computer in terms of the number and size of hard drives that can be supported on both motherboards. Firstly, the Pentium motherboard typically has two IDE connectors labeled IDE 0 and IDE 1 accordingly. These connectors are soldered directly on the motherboard and can be configured through the BIOS. Both IDE controllers on a Pentium motherboard should be able to house at least two EIDE devices each wether they be hard drives, CD-Rom drives, or tape drives.

The 486, by comparison, can typically only handle three drives and requires the use of a separate controller card inserted into an expansion card in the motherboard. The three drives a 486 can handle are typically in the form of two hard drives and a CD-Rom drive. Depending on the casing, both the Pentium and the 486 may not be able to handle more than a few devices in the system, as there may be no available drive bay able to handle the drive(s), not enough power connectors, or depending on the controller card installed within the machine, may simply not have a free cable connector to attach the data cable from the controller card to the hard drive

Master / Slave Designation

    Additionally, with Pentium systems and 486 systems, the master/slave drive designations remains roughly the same. On a Pentium system, devices are listed by connection. The connection can be one of the following:

    Primary Master
    Secondary Master
    Primary Slave
    Secondary Slave.

    On a 486 the connections are either labeled Hard Drive A or Hard Drive B, so there does exist a difference in the way a PC identifies the installed hard drives and related devices. All changes to the storage mediums in a PC must be made through the BIOS. One final point to compare is the limit of 2GB capacity on drives which are running under DOS. Windows 98, however, gets around this by using the FAT32 file format. By comparison, 486 computers tend make heavy use of DOS because the 486 is generally too slow to run the Windows 98 operating system adequately. Pentium systems are more powerful then 486 computers, and are therefore, more likely to run the Windows 98 operating system and take advantage of the FAT32 filing system.