1/16/17. Computer Programs and Processes. PHYSICAL: damage from either tampering, misuse, theft of equipment, or any combination of these

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Computer System Security Threats Computer and Processes CSC362, Information Security PHYSICAL: damage from either tampering, misuse, theft of equipment, or any combination of

(malicious or unintended) A Faraday cage is an enclosure that channels an electrical charge throughout. This blocks any RF signals that might interfere with enclosed equipment.

1 Computer System Security Threats Computer and Processes CSC362, Information Security PHYSICAL: damage from either tampering, misuse, theft of equipment, or any combination of these OPERATIONAL: outsiders taking control of the system Physical Security block or prevent outside agents from access to equipment safeguard the system from insider threats (malicious or unintended) A Faraday cage is an enclosure that channels an electrical charge throughout. This blocks any RF signals that might interfere with enclosed equipment. Basic Computer Organization HARDWARE: the devices that manage and execute computational processes SOFTWARE: programs and instructions that direct computational processes hardware components 1

Basic Computer Organization central processing unit (CPU) control unit arithmetic/logic unit (ALU) main memory input & output devices external or secondary memory architecture: functional components

2 Basic Computer Organization central processing unit (CPU) control unit arithmetic/logic unit (ALU) main memory input & output devices external or secondary memory architecture: functional components Von Neumann Instruction- Execution Cycle FETCH: the address of the next executable instruction is fetched from the Program Counter (PC) DECODE: the instruction is transferred to the Instruction Register (IR), where it is deciphered into both the type of operation prescribed and the data (if any) that is needed to perform it EXECUTE: the CPU signals the devices that will implement the prescribed operation Von Neumann Instruction- Execution Cycle and Processes programs are conceived as sequences or lists of instructions, which works more efficiently if they can be stored sequentially in contiguous memory a program is a static entity; programs direct processes a process is a sequence of individual states in which data is transformed step- by- step Depending on the nature of the instruction and the conditions of the process, the instruction- execution cycle can be more complicated 2

instructions include jump or branch instructions unconditional branch: change the address of the next executable instruction to the

3 the set of possible processor or machine instructions is called a processor machine language data movement instructions arithmetic instructions logical (comparative) instructions bitwise instructions input & output instructions control instructions control instructions include jump or branch instructions unconditional branch: change the address of the next executable instruction to the address indicated conditional branch: if the stated condition is true, change the address of the next executable instruction to the address indicated 3

It is a convenient abstraction to consider main memory supporting two separate (functional) segments control sections: instructions and static data

) modern low- level and high- level programming languages offer abstractions for aiding the development of large programs subroutines, functions,

4 It is a convenient abstraction to consider main memory supporting two separate (functional) segments control sections: instructions and static data data sections: variable data and supporting data structures (buffers, stacks, etc.) modern low- level and high- level programming languages offer abstractions for aiding the development of large programs subroutines, functions, procedures, methods, threads, etc. these sub- processes are coordinated in the program execution stack a single process contains a sequence of lightweight processes that are executed sequentially (and sometimes concurrently) 4

5 Operating System The operating system is a collection of resident programs that manage the execution of all processes on the system, control and allocate various resources in the system to these processes, and provide useful services that both protect the system and improve the human user s interaction with it. Concurrent Processing is usually supported by the OS capability for context switching save the PC from the current process save other CPU data from the interrupted process (e.g., data, stack frame, register contents) located the saved state for the new process to commence load the saved CPU data needed to resume the saved process load the PC with the starting process next executable instruction address signal the OS process manager to restart the process Concurrent Processing Concurrent Processing for multi- core architectures, the OS perceives each core as a separate processor the OS scheduler maps threads/processes to different cores each core can take single or multiple processes (SMT) The Unix ps command displaying ready processes for the CPU 5

Concurrent Processing OS Services process scheduler context switching process manager (dispatcher) memory management including the file management for the file system network protocols user interface

6 Concurrent Processing OS Services process scheduler context switching process manager (dispatcher) memory management including the file management for the file system network protocols user interface The MacOS provides similar information using the Activity Monitor OS Kernel The OS protects the system by creating a barrier through which user processes make system calls the kernel denotes the critical code that supports essential services such as memory and device management OS Memory Management the OS organizes memory for running processes into distinct segments for further protection text: machine language program data: static program values BSS: static variables not initialized heap: dynamic segment storing data generated by the process stack: organizes the execution of subroutines 6

AS/A Level Computing Syllabus 2011

AS/A Level Computing Syllabus 2011 Section 3 - System Software Mechanisms - - Machine Architecture - - Database Theory - - Programming Paradigms - Chapter 3.3 Computer Architectures & Fetch-Execute Cycle