Storage Concepts

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Personal computers have two types of storage:

1. Primary (or temporary) storage holds data only while the computer is using the data. For example, if you're woking on a document, the data is held in primary storage until the document is saved. RAM is an example of primary storage. When your computer loses power, all information in primary storage is lost.
2. Secondary storage holds data permanently (or until you delete it). When you turn on your computer, all the software and files you have saved are still available to you. Secondary storage holds data permanently, even when the computer is turned off.

There are a wide variety of secondary storage options. You are probably familiar with floppy disks and Zip disks. Hard disks are the main means of secondary storage for a personal computer. These drives can be internal (built into the computer case) or external (removable drive which plugs into a port on the back of the computer). Hard disks are faster and offer more space than other storage devices.

	The space between the read-write heads and the platters is smaller than the width of a human hair. Particles such as dust and smoke can interfere with the read-write heads, causing the disk to crash, and you to lose data. Therefore, it is important to keep the area around your computer free from dust and smoke.
	When buying a computer or a new hard drive, there are three factors to consider: Capacity—How much data can the drive hold? Capacity is measured in gigabytes. (One gigabyte equals 1,000 megabytes.) Most new computers come with hard disks 10 GB - 40 GB. Data rate—How quickly can the drive send data to the CPU? Data rate is measured in megabytes per second. Today's data rates average 40-60 MB per second. With data rate, a higher number is better. Seek time—How quickly can the drive respond to a request from the CPU? Seek time is measured in milliseconds (ms), usually 8-12 ms for new systems. With seek time, a smaller number is better.
	As large hard drives become more common, the amount of space available can become unwieldy. You can organize your hard drive by dividing it into smaller drives—called partitions. Each partition is assigned its own drive letter, making it easy to have one drive for applications only, another for personal files, another for business purposes, etc.

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Parts of the hard drive:

Platters—discs where data is written to. Most hard drives have multiple platters. When a platter is formatted so it can store data, it is organized into:

• Tracks—rings
• Sectors—pieces of each ring (track)

Spindle—holds the platters and attaches them to the drive which causes them to spin.

Read-write heads—move across the platters using magnetic fields to read data from and write data to the platters.