Magnetic Media

Magnetic media range from some of the smallest capacity storage devices, floppy disks, to the largest capacity devices, hard disk drives. The floppy disk is no longer used to distribute operating systems, though, because of the increasingly large size of current operating systems. The last major distribution of Windows using floppy disks was Windows 95, which occupied 30 diskettes.

Zip disks, removable storage drives produced by Iomega, allow users to store much larger amounts of data than a floppy disk can hold—although Zip disks are physically not much bigger than floppy disks. These drives were once very popular, and many machines came with a Zip drive as standard equipment. But, their use declined with the wide availability of CD-RW and DVD-RW drives and the reduced cost of blank CD-R and DVD-R disks.

Smaller portable drives are being manufactured with larger capacities. For example, Mini USB storage device offers 512MB, 1GB, or 8GB of storage capacity on a storage device the size of a car key. Another portable storage device offered by Iomega is the pocket-size HDD Desktop external hard drive. It is available from 40GB all the way to 1TB of storage capacity. These devices can be connected to a USB or FireWire port.

Fixed (non-removable) hard disk drives are still the main storage medium for computers today. They can hold more data than any of the removable media types, optical or magnetic. On most personal machines, the operating system, application programs, and user data all reside on one hard drive. The smallest hard drives today, which are typically found in laptops, hold about 160 GB. When purchased separately, hard drives run from 20 GB up to around 1TB, with the limit continuing steadily upward each year. Another important characteristic when comparing hard disk drives is the speed at which a disk drive rotates, since this limits the rate at which bits can be transferred between the drive and the computer. Slower drives spin at 4200 rpm (i.e. laptop computers); faster ones, at 15,000 rpm. If a hard drive is to be used in a performance-critical application, such as a database server, the data transfer rate is an important consideration. This rate will be affected by several other factors besides the rotation speed of the disk and latency (time it takes to access the first bit of data)—such as the type of disk controller selected and the type of memory architecture the computer uses. Refer to the sections on benchmarking in 2.1.1 Processor Basics and 2.5.2 Bottlenecks to find more information on this subject.

Optical versus Magnetic

Let us briefly compare optical and magnetic storage technologies. Optical media are more durable. They are not ruined by dust or moisture, nor are they vulnerable to electrical damage (however, they can be damaged by physical damages such as scratches). Optical media's MTBF rating (average life expectancy) ranges between 30 and 300 years, while magnetic media utilize magnetic properties that have a MTBF of about 3–7 years. Optical media are also less expensive per MB than magnetic disks. A box of blank CD-Rs is twice as expensive as a box of ten floppy disks. On the other hand, magnetic disks, with the exception of floppy disks, can be written and read faster than optical disks. It takes at about 8 minutes to fill up a 700 MB recordable CD. A hard disk drive can store the same amount of data in less than a minute. Finally, most hard disk drives offer greater capacity than any currently available optical device.