• An OS is a program that acts as an intermediary between a user of a computer and the computer h... more • An OS is a program that acts as an intermediary between a user of a computer and the computer hardware • Goals: Execute user programs, make the comp. system easy to use, utilize hardware efficiently • Computer system: Hardware ↔ OS ↔ Applications ↔ Users (↔ = 'uses') • OS is: • Resource allocator: decides between conflicting requests for efficient and fair resource use • Control program: controls execution of programs to prevent errors and improper use of computer • Kernel: the one program running at all times on the computer • Bootstrap program: loaded at power-up or reboot • Stored in ROM or EPROM (known as firmware), Initializes all aspects of system, loads OS kernel and starts execution • I/O and CPU can execute concurrently • Device controllers inform CPU that it is finished w/ operation by causing an interrupt • Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines • Incoming interrupts are disabled while another interrupt is being processed • Trap is a software generated interrupt caused by error or user request • OS determines which type of interrupt has occurred by polling or the vectored interrupt system • System call: request to the operating system to allow user to wait for I/O completion • Device-status table: contains entry for each I/O device indicating its type, address, and state • OS indexes into the I/O device table to determine device status and to modify the table entry to include interrupt • Storage structure: • Main memory – random access, volatile • Secondary storage – extension of main memory That provides large non-volatile storage • Disk – divided into tracks which are subdivided into sectors. Disk controller determines logical interaction between the device and the computer. • Caching – copying information into faster storage system • Multiprocessor Systems: Increased throughput, economy of scale, increased reliability • Can be asymmetric or symmetric • Clustered systems – Linked multiprocessor systems • Multiprogramming – Provides efficiency via job scheduling • When OS has to wait (ex: for I/O), switches to another job • Timesharing – CPU switches jobs so frequently that each user can interact with each job while it is running (interactive computing) • Dual-mode operation allows OS to protect itself and other system components – User mode and kernel mode • Some instructions are only executable in kernel mode, these are privileged • Single-threaded processes have one program counter, multi-threaded processes have one PC per thread • Protection – mechanism for controlling access of processes or users to resources defined by the OS • Security – defense of a system against attacks • User IDs (UID), one per user, and Group IDs, determine which users and groups of users have which privileges
• An OS is a program that acts as an intermediary between a user of a computer and the computer h... more • An OS is a program that acts as an intermediary between a user of a computer and the computer hardware • Goals: Execute user programs, make the comp. system easy to use, utilize hardware efficiently • Computer system: Hardware ↔ OS ↔ Applications ↔ Users (↔ = 'uses') • OS is: • Resource allocator: decides between conflicting requests for efficient and fair resource use • Control program: controls execution of programs to prevent errors and improper use of computer • Kernel: the one program running at all times on the computer • Bootstrap program: loaded at power-up or reboot • Stored in ROM or EPROM (known as firmware), Initializes all aspects of system, loads OS kernel and starts execution • I/O and CPU can execute concurrently • Device controllers inform CPU that it is finished w/ operation by causing an interrupt • Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines • Incoming interrupts are disabled while another interrupt is being processed • Trap is a software generated interrupt caused by error or user request • OS determines which type of interrupt has occurred by polling or the vectored interrupt system • System call: request to the operating system to allow user to wait for I/O completion • Device-status table: contains entry for each I/O device indicating its type, address, and state • OS indexes into the I/O device table to determine device status and to modify the table entry to include interrupt • Storage structure: • Main memory – random access, volatile • Secondary storage – extension of main memory That provides large non-volatile storage • Disk – divided into tracks which are subdivided into sectors. Disk controller determines logical interaction between the device and the computer. • Caching – copying information into faster storage system • Multiprocessor Systems: Increased throughput, economy of scale, increased reliability • Can be asymmetric or symmetric • Clustered systems – Linked multiprocessor systems • Multiprogramming – Provides efficiency via job scheduling • When OS has to wait (ex: for I/O), switches to another job • Timesharing – CPU switches jobs so frequently that each user can interact with each job while it is running (interactive computing) • Dual-mode operation allows OS to protect itself and other system components – User mode and kernel mode • Some instructions are only executable in kernel mode, these are privileged • Single-threaded processes have one program counter, multi-threaded processes have one PC per thread • Protection – mechanism for controlling access of processes or users to resources defined by the OS • Security – defense of a system against attacks • User IDs (UID), one per user, and Group IDs, determine which users and groups of users have which privileges
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