Hardware Reference
In-Depth Information
as the ASCII character set. The original ASCII standard called for 7-bit codes, so there were
128 combinations possible. In 1981, IBM introduced an 8-bit version called the extended
ASCII character set for use on the IBM PC, which added another 128 combinations used for
math, graphical, and foreign language characters, for a total of 256 combinations.
Nowadays, a different encoding system, called Unicode, is the predominantly used
standard. Unicode consists of more than 109,000 characters covering multiple languages.
Unicode can be implemented with different character encodings. The most common one
is UTF-8, which is very similar to Extended ASCII, using the same one-byte values for the
basic set of ASCII characters.
Floppy disk drives, once the most popular and affordable storage medium
for PCs, are now obsolete. Very rarely will a new system come with a
floppy disk drive, although you might occasionally encounter one in an
old PC. You don't need to know anything about them for the Strata exam
except that the acronym FDD stands for floppy disk drive.
Hard Drives
A
hard drive
(or hard disk) is a sealed stack of metal platters, each with a read-write head
on a retractable arm that reads data from and writes data to the platters by magnetizing
bits of iron oxide particles on the platters in patterns of positive and negative polarity. As a
hard disk operates, the platters rotate at a high speed, and the read/write heads hover just
over the disk surfaces on a cushion of air generated by the spinning.
Figure 2.8 shows the inside of a hard disk drive. You wouldn't normally see one this way
because the metal box in which a hard disk is encased is permanently sealed; if you take it
apart, you ruin it. The platters are typically 3.5” in diameter for full-size hard disk drives
(for desktop PCs) and 2.5” for smaller hard disk drives used in notebook PCs.
FIGURE 2.8
Inside of a hard disk drive
Photo credit: Mfield, Matthew Field,
http://www.photography.mattfield.com
