Page 574 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

“Essential Security Protection Mechanisms” later in this chapter, you’ll
learn how the principle of process isolation can be used to ensure that

processes don’t have access to read or write to memory spaces not
allocated to them. If you’re operating in a multilevel security
environment, it’s especially important to ensure that adequate
protections are in place to prevent the unwanted leakage of memory
contents between security levels, through either direct memory access
or covert channels (a full discussion of covert channels appears later in
this chapter).

Storage

Data storage devices make up the third class of computer system
components we’ll discuss. These devices are used to store information
that may be used by a computer any time after it’s written. We’ll first
examine a few common terms that relate to storage devices and then
cover some of the security issues related to data storage.

Primary vs. Secondary

The concepts of primary and secondary storage can be somewhat

confusing, especially when compared to primary and secondary
memory. There’s an easy way to keep it straight—they’re the same
thing! Primary memory, also known as primary storage, is the RAM
that a computer uses to keep necessary information readily available
to the CPU while the computer is running. Secondary memory (or
secondary storage) includes all the familiar long-term storage devices
that you use every day. Secondary storage consists of magnetic and

optical media such as HDD, SSDs, flash drives, magnetic tapes, CDs,
DVDs, flash memory cards, and the like.

Volatile vs. Nonvolatile

You’re already familiar with the concept of volatility from our
discussion of memory, although you may not have heard it described
using that term before. The volatility of a storage device is simply a
measure of how likely it is to lose its data when power is turned off.
Devices designed to retain their data (such as magnetic media) are

classified as nonvolatile, whereas devices such as static or dynamic