Introduction OS Flashcards
Multiprocessors systems dominates
the computing market
Advantages of it include:
a. Increased throughput
b. Economy of scale
c. Increased reliability – graceful degradation
or fault-tolerant.
There are two kinds of multiprocessing
Asymmetric Multiprocessing and Symmetric multiprocessing
Asymmetric Multiprocessing
– Each processor is assigned a specific task:
\+ A boss processor controls the system.
\+ The other processors look to the boss
for instruction.
Symmetric multiprocessing
– Each processor performs all tasks
Multicore
The CPU that design is to include multiple
computing cores on a single chip. Or to put it simply: Multicore mean 2 or more than 2 CPU equipped in one chip.
Singlecore
Which mean only 1 CPU equipped in one chip.
Muliticore can be more efficient than multiple
chips with single cores
Because ON-CHIP communication is faster
than BETWEEN-CHIP communication
Interrupts
are signals sent to the CPU by external devices, normally I/O devices. They tell the CPU to stop its current activities and execute the appropriate part of the operating system
There are three types of interrupts
- Hardware Interrupts
- Software Interrupts
- Traps
Hardware Interrupts
are GENERATED by hardware devices to SIGNAL that they need some attention from the OS
Hardware Interrupts
are generated by hardware devices to signal that they need some attention from the OS
Software Interrupts
are generated by programs when they want to request a system call to be performed by the operating system
Traps
are generated by the CPU itself to INDICATE that some error or condition occurred for which assistance from the OS is needed
There are two CPU Execution Mode
- User mode
- Kernel or supervisor mode
User mode
is restricted in that certain instructions cannot be executed, certain registers cannot be accessed, and I/O devices can not be accessed
- Can only execute a subset of instructions
- Can only reference a subset of memory locations
Kernel or supervisor mode
Kernel mode has NONE of the restrictions
- A system call will set the CPU to kernel mode, as will traps and interrupts
- Can execute all machine instructions
- Can reference (?) all memory locations
Context switch
switching from running a user level process to the OS kernel and to other user processes before the current process is resumed
The CPU performs the following actions in response to an interrupt
- Using the pointer to the current process control block
- The state and all register values for the process
are saved for use when the process is later
restarted
- The state and all register values for the process
- The CPU mode bit is switched to supervisory mode
- Using the pointer to the interrupt handler table and the interrupt vector
-The location of the kernel code to execute is
determined- The interrupt vector is the interrupt request
(IRQ) for hardware interrupts and an argument to
the interrupt assembly language instruction for
software interrupts
- The interrupt vector is the interrupt request
- Processing is switched to the appropriate portion of the kernel
There are 4 broad tasks performed by an operating system
Process Management
Memory Management
File System Management
Device Management
Process Management
A process is an executing program
It consists of code, data, a certain set of resources allocated to it, and one or more threads of
execution through the code
The OS manages the allocation of resources to these processes, and also provides system calls to
manage these processes
Memory Management
Memory must be shared between the OS and an application program
The OS must manage the allocation of memory to processes and control the memory management
hardware that determines which memory locations a process may access
File System Management
Computers process information that must be transmitted, processed, and stored
File systems are an abstract organized collection of file system objects
The OS provides primitives to manipulate these objects process may access
Device Management
Information is sent through a computer’s input and output devices
Processes access these devices using the system call interface
The OS tries to manage devices in a manner that makes them efficiently shared among all processes
requiring them
A system call is a programming interface to the services provided by the OS, typically written in C/C++
Design Goals
At the highest level, system design is dominated by the choice of hardware and system type
Beyond this level, the requirements can be divided into two groups:
User goals: include convenience, reliability, security, and speed
System goals: include ease of design, implementation, maintenance, flexibility, and efficiency
Implementation
o Operating systems were firstly written in assembly, but nowadays C/C++ is the language
commonly used
o Small blocks of assembly code are still needed, especially related to
* Low level I/O functions in device drivers * Turning interrupts on and off * The Test and Set Instruction for Synchronization Facilities
o Using higher level languages allows the code to be written faster
* It also makes the OS much easier to port to
different hardware platforms
Implementation
o Operating systems were firstly written in assembly, but nowadays C/C++ is the language
commonly used
o Small blocks of assembly code are still needed, especially related to
* Low level I/O functions in device drivers * Turning interrupts on and off * The Test and Set Instruction for Synchronization Facilities
o Using higher level languages allows the code to be written faster
* It also makes the OS much easier to port to
different hardware platforms
