(^196) PC Hardware: A Beginner’s Guide
Ten different RAID levels exist—0 through 7, 10, and 53, and each one is more com-
plicated than its predecessor. In general usage, there are only four RAID levels—0, 1, 3,
and 5—used on most systems. Here is a brief overview of these RAID levels:
RAID 0 (Striped disk array without fault tolerance) This level provides
data striping but does not include any mirroring or other redundancy. If a
disk drive is lost, the portion of the data stored on it is also lost.
RAID 1 (Mirroring and duplexing) A very common RAID level on high-
volume disk systems. It features complete data redundancy and does not
require the data to be rebuilt. Should a disk failure occur, a copy of the data
only needs to be loaded to the replacement disk (usually a hot-swap disk).
RAID 3 (Parallel transfer with parity) This level is very much like Level 0,
except that it sets aside a dedicated disk for storing parity and error-correcting
code (ECC) data that can be used to reconstruct the data should a hard disk fail.
RAID 5 (Data striping with parity) On systems requiring a high-degree of
data protection and availability, this RAID level is popular. RAID 5 provides
for data striping at the character level and implements error correction at the
stripe level. The error correction data is stored on a separate disk from the
data it represents. RAID 5 requires at least three disk drives to implement.
Floppy Disk Drives
Although manufacturers have been trying for years to replace the floppy disk, a.k.a.
diskette, with a device that holds more data, the 3.5-inch floppy disk drive is still very
commononmostPCssoldtoday.Thefloppydiskhassurvivedwellbeyondwhatanyone
expected. It has changed in size over the years and is available in drives that fit inside the
system case as well as outside. The floppy disk has come in a variety of sizes over its life-
time, but for about the past ten years the most popular size has been the 3.5-inch diskette.
Figure 9-10 contrasts the older 5.25-inch diskette to the 3.5-inch disk.Figure 9-10. The 3.5-inch and 5.25-inch floppy disks