A hard drive stores program files and data files. Data files can be almost anything; help files, support files, letters, contracts, accounting journals, etc..

Also called a fixed disk. Resides in an internal drive bay. Requires a power connector and a data connector. Older parallel drives: (Now called PATA) Really Old: 40-wire ribbon connector Newer Old: 80-wire ribbon cable Both were stiff, cold, short, and could block airflow IDE/ATA; Integrated drive Electronics/AT Attached (AT= Advanced Technology. From the IBM PC AT, 1982) Anything with IDE, EIDE, AT, ATA, DMA, Ultra DMA, or ATAPI in the name Max transfer rate about 133 MB/sec Newer Serial Drives: (Now called SATA) PCI-e, serial connection Seven-wire connector; Thinner, longer, and more flexible 1st Gen=150 MB/sec; 2nd Gen=300 MB/sec; Roadmap leads to 600 MB/sec Most physical drives are barely fast enough to saturate the 150 MB/sec 1st Gen

PATA on the Left SATA on the Right

Typical Hard Drive Configuration

Disks are called Platters. Typical drives have three platters. Each side of a platter is called a surface.

The actuator assembly moves the read/write heads.

There is one read/write head for each surface.

Spinning platters write data in concentric circles called Tracks Spinning platters write data in concentric circles called Tracks. The yellow is a track. Tracks are numbered starting from zero at the outermost track. Tracks are further subdivided into segments of arc called Sectors. The blue is a sector. Each sector in a drive holds 512 Bytes. Notice the outer sectors are physically longer than the inner sectors, but still hold 512 Bytes. Most drives since the early 1990s use Zone Bit Recording that sets the sector length so that there are more sectors on the outer tracks. The sector that would be sector zero, is called the Master Boot Record. Therefore, the first usable sector is numbered sector 1, again on the outer track.

Structure of a Master Boot Record Address Description Size in bytes Hex Dec 0000 Code Area max. 446 01B8 440 Optional Disk signature 4 01BC 444 Usually Nulls; 0x0000 2 01BE 446 Table of primary partitions (Four 16-byte entries, IBM Partition Table scheme) 64 01FE 510 55h MBR signature; 0xAA55 01FF 511 AAh MBR, total size: 446 + 64 + 2 = 512 Code Area: Master boot program that calls the OS boot record. Table of primary partitions: Contains partition information about the hard disk. A single hard drive can be divided into a number of drive letters. A single hard drive can contain more than one operating system. I(f it does, they cannot generally communicate with each other. It’s like having more than one computer in one computer. Each of these entities would be contained in a separate drive partition.

Hard drive capacities have reached one terabyte for internal drives. External drives can be connected through a USB port, or through a firewire port. Large capacity hard drives are especially important for people who work with large graphic files and video. A one-hour mini DV video tape can be a 20 GB download onto your hard drive. Editing it would require a second file of at least equal size. Hi-Def would be larger.

The most important word in computing is backup. Many external hard drives come with software that will automatically back up your PC’s main hard drive. Archiving is saving old computer data files that you may someday, but probably never, need.

A certain percentage of hard drives fail each year A certain percentage of hard drives fail each year. If yours is one of them, and your PC is not too old, it may be cost efficient to replace the old, dead drive with a new one. Remember, you’ll need OS installation media.

Hard drive storage capacity is measured in gigabytes (GB), or terabytes (TB) these days.

Most desktop hard drives spin at 7200 RPM Most desktop hard drives spin at 7200 RPM. Drives are available that spin at 10,000 and 15,000 RPM, but they are very pricey. (RPM means revolutions-per-minute.) Most laptop drives spin at 5400 RPM. That’s one reason laptops typically seem to operate more slowly than an equivalently equipped desktop. Average access time is the average time it takes for the read/write heads to locate the sector to be accessed. Average access time is measured in milliseconds, typically around 8ms.

The word “cache” means a store of things that will be required in the future. In computing, it is a memory storage area used by fast devices to access data stored in slower devices. Disk cache is a memory area, now part of the disk drive itself, that stores the most recently used data and instructions retrieved from the drive. During the next access, the drive will Look in the cache memory for the requested data. If it is there, the transfer will be thousands of times faster than if the drive itself has to be accessed.

Deleting unwanted files, Internet histories, and cookies can free up space on your hard drive. You can always burn them to CD or DVD, if you feel you just can’t part with them completely. You don’t delete programs in Windows, you uninstall them. You can always reinstall them, if you have the original install disks.

Remember, saving old stuff is also called archiving.

Windows Backup: Start/All Programs/Accessories/System Tools/Backup Google backup programs, and get a bunch Full Backup means everything. Incremental Backup means backing up only those files that have been changed since the last backup.

A virus is a program intended to do damage to your PC. Viruses are transmitted through infected e-mails, downloads, floppy disks, CDs, DVDs, Flash Drives, hackers that can access your PC while you’re on-line without you knowing it, or anything else that has been infected that you connect to your PC. Your PC should be protected with a complete set of programs that include a firewall, virus scanner, and anti-spyware at the least. Popular software names are Norton, McAfee, ZoneAlarm, Kasperski, AVG, and others.

Fragmentation happens whenever your PC is turned on Fragmentation happens whenever your PC is turned on. Parts of files get spread apart. The read/write heads have to work harder to read and write. Your drives will wear faster, and the probability of losing data on your drive increases. Defragmentation puts file pieces back together. Windows: Start/All Programs/Accessories/System Tools/Disk Defragmenter

Parts of hard drives have errors when they are manufactured Parts of hard drives have errors when they are manufactured. These are mapped out by the formatting program, So the operating system can’t use them. Other parts of drives may fail during use. Check your drives periodically For errors.

A second hard drive can allow you to install your software on your primary drive, and use your secondary drive For data storage. That helps increase efficiency.