Computer Architecture, Operation of Microprocessor, and the CISSP Exam
Certified Information Systems Security Professional (CISSP) is an independent information security
certification granted by the International Information System Security Certification Consortium.
CISSP is a standardized, vendor-neutral certification program that provided structure and demonstrated
competence relevant to information security professionals.
The basic operation of a microprocessor consists of two distinct phases: fetch and execute.
(It's not too different from what your dog does: You throw the stick, and he fetches the stick.)
During the fetch phase, the CPU locates and retrieves a required instruction from memory. During
the execute phase, the CPU decodes and executes the instruction. These two phases make up a
basic machine cycle that's controlled by the CPU clock signals. Many complex instructions require
more than a single machine cycle to execute.
The four operating states for a computer (CPU) are:
• Operating (or run) state: The CPU executes an instruction or instructions.
• Problem (or application) state: The CPU calculates a solution to an application-based
problem. During this state, only a limited subset of instructions (non-privileged instructions)
• Supervisory state: The CPU executes a privileged instruction, meaning that
instruction is available only to a system administrator or other authorized user/process.
• Wait state: The CPU hasn't yet completed execution of an instruction and
must extend the cycle.
The two basic types of CPU designs used in modern computer systems are:
• Complex-Instruction-Set Computing (CISC): Can perform multiple operations per
single instruction. Optimized for systems in which the fetch phase is the longest part of the
instruction execution cycle. CPUs that use CISC include Intel x86, PDP-11, and Motorola 68000.
• Reduced-Instruction-Set Computing (RISC): Uses fewer, simpler instructions
than CISC architecture, requiring fewer clock cycles to execute. Optimized for systems in which
the fetch and execute phases are approximately equal. CPUs that have RISC architecture include
Alpha, PowerPC, and SPARC.
Microprocessors are also often described as scalar or superscalar. A scalar processor executes
a single instruction at a time. A superscalar processor can execute multiple instructions concurrently.
Finally, many systems (microprocessors) are classified according to additional functionality
(which must be supported by the installed operating system):
• Multitasking: Alternates the execution of multiple subprograms or tasks
on a single processor.
• Multiprogramming: Alternates the execution of multiple programs on a single processor.
• Multiprocessing: Executes multiple programs on multiple processors simultaneously.
Two related concepts are multistate and multiuser systems that, more correctly, refer
to operating system capabilities:
• Multistate: The operating system supports multiple operating states, such
as single-user and multiuser modes in the UNIX/Linux world and Normal and Safe modes in the
• Multiuser: The operating system can differentiate between users. For example,
it provides different shell environments, profiles, or privilege levels for each user, as well
as process isolation between users.
An important security issue in multiuser systems involves privileged accounts, and programs
or processes that run in a privileged state. Programs such as su (UNIX/Linux) and RunAs (Windows)
allow a user to switch to a different account, such as root or administrator, and execute privileged
commands in this context. Many programs rely on privileged service accounts to function properly.
Utilities such as IBM's Superzap, for example, are used to install fixes to the operating system
or other applications.
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