50 Computer Service and Repair
command.com
produces an MS-DOS command
prompt, whereas
cmd.exe
produces a 32-bit console
application. Both
command.com
and
cmd.exe
are
executable files. An executable file has an
.exe
or
.com
file extension. Executable files are complete
software programs that run when the file name is
entered at the command prompt. Similar results
occur when a program is selected from the
Start
menu or when clicking a desktop shortcut that
represents a program.
Command.com
can be run in Windows Vista,
Windows 7, and Windows 8 when required for
legacy programs. It is run as a DOS interpreter
inside a Windows NT virtual machine. The
Windows NT virtual machine is not a physical
machine. A virtual machine or computer only
exists in the computer’s memory but appears
to the user as a real machine or computer. This
command interpreter contains many of the same
DOS internal and external commands, plus
additional commands.
Windows Features
The most important Windows features are
introduced in this section. Not all of the features
are available to all versions of Windows. You can
use the table Figure 2-16 to quickly identify which
version of Windows has the feature integrated
into the operating system. Features unique to
Windows 8 are covered in the following section.
For a more detailed list of Windows operating
system features, check the Microsoft website.
You can conduct an Internet search using the key
terms ”Microsoft Windows feature comparison.”
Be sure to add the operating version or versions in
the search key terms.
The A+ Certification requires knowledge of
a variety of Windows operating systems and
features. Always check the CompTIA website
for a list of operating systems that are covered
on the exams.
A+ Note
Windows Aero
Windows Aero is an enhanced user interface.
It is much more sophisticated than the user
interfaces of operating systems previous to
Windows Vista. It is designed to have a glass-like
appearance with various degrees of transparency,
Figure 2-17. The Windows Aero feature is one
of the main reasons a greater amount of RAM
and a quality 3-D graphics card or motherboard
is required. Windows Aero is also one of the
main reasons for the slow performance of
Windows Vista when compared to Windows XP
loaded on a similar PC.
BitLocker Drive Encryption
BitLocker Drive Encryption is an encryption
feature. Encryption is the process of rendering
the contents of a file unreadable by people other
than those who are allowed to read it. It differs
from earlier versions of file encryption in that it
encrypts the entire volume, including the system
files required for startup and logon, rather than
just data files. BitLocker ensures that data remains
encrypted even when the operating system is not
running. For example, if someone removes a hard
drive and then attempts to access the data from
another computer using a different operating
system or software utility, BitLocker prevents
the data from being accessed because the data
remains encrypted.
BitLocker is transparent to the user after
it is activated. It is designed to be used with a
computer that has a Trusted Platform Module
(TPM) or firmware that can read a USB flash
drive. The TPM is a microchip designed to work
with the BitLocker software. The TPM ensures
that encryption is intact throughout the boot
sequence of the computer. If the TPM is missing
or has changed, the user is required to supply
a password to access the encrypted data. If
BitLocker is configured on a system that does
not have a TPM, a startup key is required when
it is first configured. A typical startup key is a
software program loaded on a USB flash drive.
The software program contains the encryption
key used to access the encrypted drive.