Illustration 1.1 Tracks and Sectors



Most magnetic storage disks now use multiple sides of multiple platters. In order to determine the size of a disk, you must know how many cylinders are in a drive. A cylinder is a barrel-shaped cross section of a disk, consisting of a circular strip from each side of each platter.






Calculating Disk Space



Cylinders: 12288
Heads: 16
Sectors per track: 63

Cylinders x Heads x Sectors x 512 = 6,341,787,648

6,341,787,648 bytes = 6.341 GB

This is something that is good to know but won’t be needed for trouble shooting purposes.

Binary Vs. Base 10

Humans count in base 10 (i.e. 1 2 3… 9 10..1000..1,000,000.. etc)

101 = 10, 103 = 1,000, 106 = 1,000,000 109 = 1,000,000,000

Computers count in binary (i.e. 1 2 4..16 32.. 1024.. 1048576.. etc)

2¹ = 2, 2¹°= 1,024, 2²° = 1,048,576, 2³° = 1,073,741,824

Bit = 1 or 0 is the smallest single piece of information that a computer can keep track of.
Byte = 8 Bits. Bytes are normally capital B’s while bits are lower case b’s. 8 B is read 8 Bytes while 8 b is read 8 bits.
Kilobyte = 1000 or 1024 bytes. Depending on the counting system you are using. Abbreviated KB
Megabytes = 1000 or 1024 kilobytes. Once again depending on the counting system. Abbreviated MB
Gigabytes =1000 or 1024 megabytes. Depends on the counting system used. Abbreviated GB
Terabytes = 1000 or 1024 gigabytes. Pattern continues. Abbreviated TB

It is important to understand the difference between base 10 and binary because when a device that states a storage capacity it often times states the decimal value while the computer can only use the binary value. This will show up as a difference between what is labeled on the front of the computer and what a customer finds when viewing the hard drive properties, as an example. There is a common misconception about the stated storage space. The closest that computers come to 1000 is 1024 or 210. In our example of calculating disk space we see a drive that is 6.341 billion bytes.

 

In this example the hard drive manufacture will sell the hard drive as 6.3 GB but when you put it in your computer you actually only have 5.9 GB that you can use.



Magnetic Storage Types

Emachines only supports two types of magnetic storage, the Floppy Disk Drive (FDD) and the Hard Disk Drive (HDD)

Floppy Disk Drive

The 3.5 floppy drive is a technology that has been in the industry since 1984. Throughout the 1990’s the 3.5 drive dominated the market as the popular back up and transport mechanism. Although very common, the floppy drive is starting to become obsolete and in some of our newest models the floppy drive has been excluded. The floppy disk drive has a drive motor that will spin the disk, and two read\write heads that read the disk (One on top, one on the bottom)

Physical Size: 3.5 Inches (90 mm)
Capacity: 1.44 MB (720 per side)

Note: The floppy disk has a thin magnetic disk that is protected by a hard plastic outer casing. A small window cut in the plastic to allow the read\write heads access to the film. This window is protected by a spring loaded sliding door.

Caution: The floppy drive connects the computer motherboard via the 34 pin Floppy Drive Controller (FDC) cable. If the cable is plugged in backwards the activity light will stay on constantly and the drive will not read any disks.

Hard Disk Drive

Hard Disk Drives have been included in all modern computers for the last 20 years. The hard disk drive is the primary storage device. Most eMachines computers now ship with drives that are 40 GB or higher. A common misunderstanding among customers is confusing the Hard Disk Drive with the system memory. The hard drive’s main job is to store large amounts of data even when the computer is turned off. There are important things to consider when purchasing a hard drive.

• Spin Rate – The spin rate is the speed that the drive will rotate the internal platters, a faster Spin rate typically will indicate a lower seek time. 5400 – 7200 RPM are common.
• Drive capacity – The drive size is the measurement of how much information it can hold. 20 – 100 GB sizes are common.
• Interface Type – The interface type is how the hard drive will connect to the computer. EIDE is currently the only type that eMachines supports.

Common Dangers
Magnetic storage has two major hazards to be aware of.

Magnetic Fields: The way that information is contained on the disk makes it vulnerable to magnetic fields. If you place a magnetic field too close to a disk, it is possible that the information on the disk may be lost.

Bad Sectors: Information is stored by changing the polarity of a sector, eventually after changing the polarity enough times, the sectors stop holding a charge. When a sector looses its ability to hold information it is called a bad sector. You can Identify a bad sector with the operating systems build in disk utilities

• Scandisk: Windows 9X, use the through option to check for bad sectors.
• ChkDsk: Windows XP, Use the Scan and attempt recovery of bad sectors

Summary

In this presentation you should have learned about magnetic storage and the devices that use magnetism in order to store information on a disk or platter. Magnetic storage is the most common method used in Large Storage devices such as hard drives. Special care should be taken to protect Magnetic devices from outside magnetic fields because data loss my result.