System Generation
A process that creates a particular and uniquely specified operating system; it combines user-specified options and parameters with manufacturer-supplied general-purpose or nonspecialized program subsections to produce an operating system (or other complex software) of the desired form and capacity. Abbreviated sysgen.
System Boot
Operating system must be made available to hardware so hardware can start it
Operating system must be made available to hardware so hardware can start it
- Small piece of code – bootstrap loader, locates the kernel, loads it into memory, and starts it
- Sometimes two-step process where boot block at fixed location loads bootstrap loader
- When power initialized on system, execution starts at a fixed memory location
- Firmware used to hold initial boot code
- Virtual Machine
- Is a software implementation of a machine (computer) that executes programs like a real machine.
- Provides a complete system platform which supports the execution of a complete operating system (OS).
- Takes the layered approach to its logical conclusion. It treats hardware and the operating system kernel as though they were all hardware.
IMPLEMENTATION
- Modes: - virtual user mode and virtual monitor mode,
- Actual user mode and actual monitor mode
-Time - Whereas the real I/O might have taken 100 milliseconds, the virtual I/O might take less time (because it is spooled) or more time (because it is interpreted.)
- The CPU is being multi-programmed among many virtual machines, further slowing down the virtual machines in unpredictable ways.
BENEFITS
- concept provides complete protection of system resources since each virtual machine is isolated from all other virtual machines.
- perfect vehicle for operating-systems research and development. System development is done on the virtual machine, instead of on a physical machine and so does not disrupt normal system operation.
- multiple OS environments can co-exist on the same computer, in strong isolation from each other
- the virtual machine can provide an instruction set architecture (ISA) that is somewhat different from that of the real machine
- application provisioning, maintenance, high availability and disaster recovery
EXAMPLE
- A program written in Java receives services from the Java Runtime Environment (JRE) software by issuing commands to, and receiving the expected results from, the Java software. By providing these services to the program, the Java software is acting as a "virtual machine", taking the place of the operating system or hardware for which the program would ordinarily be tailored.
System Structure
Simple Structure
– any part of the system may use the functionality of the rest of
the system
– MS-DOS (user programs can call low level I/O routines)
Layered Approach
– layer n can only see the functionality that layer n-1 exports
– provides good abstraction from the lower level details
• new hardware can be added if it provides the interface required of a particular layer
– system call interface is an example of layering
– can be slow if there are too many layers
Simple Structure
– any part of the system may use the functionality of the rest of
the system
– MS-DOS (user programs can call low level I/O routines)
Layered Approach
– layer n can only see the functionality that layer n-1 exports
– provides good abstraction from the lower level details
• new hardware can be added if it provides the interface required of a particular layer
– system call interface is an example of layering
– can be slow if there are too many layers
System Calls
Provide the interface between application programs and the kernel
Are like procedure calls
– take parameters
– calling routine waits for response
Permit application programs to access protected resources
Process Control
– create/terminate a process (including self)
File Management
– open, create
– read, write
– close, delete
– get or set file attributes
Also referred to as simply a file system or filesystem. The system that an operating system or program uses to organize and keep track of files. For example, a hierarchical file system is one that uses directories to organize files into a tree structure.
Although the operating system provides its own file management system, you can buy separate file management systems. These systems interact smoothly with the operating system but provide more features, such as improved backup procedures and stricter file protection.
Device Management
Device Management is a set of technologies, protocols and standards used to allow the remote management of mobile devices, often involving updates of firmware over the air (FOTA). The network operator, handset OEM or in some cases even the end-user (usually via a web portal) can use Device Management, also known as Mobile Device Management, or MDM, to update the handset firmware/OS, install applications and fix bugs, all over the air. Thus, large numbers of devices can be managed with single commands and the end-user is freed from the requirement to take the phone to a shop or service center to refresh or update.
Information Maintenance
– get time
– set system data (OS parameters)
– get process information (id, time used)
Provide the interface between application programs and the kernel
Are like procedure calls
– take parameters
– calling routine waits for response
Permit application programs to access protected resources
Process Control
– create/terminate a process (including self)
File Management
– open, create
– read, write
– close, delete
– get or set file attributes
Also referred to as simply a file system or filesystem. The system that an operating system or program uses to organize and keep track of files. For example, a hierarchical file system is one that uses directories to organize files into a tree structure.
Although the operating system provides its own file management system, you can buy separate file management systems. These systems interact smoothly with the operating system but provide more features, such as improved backup procedures and stricter file protection.
Device Management
Device Management is a set of technologies, protocols and standards used to allow the remote management of mobile devices, often involving updates of firmware over the air (FOTA). The network operator, handset OEM or in some cases even the end-user (usually via a web portal) can use Device Management, also known as Mobile Device Management, or MDM, to update the handset firmware/OS, install applications and fix bugs, all over the air. Thus, large numbers of devices can be managed with single commands and the end-user is freed from the requirement to take the phone to a shop or service center to refresh or update.
Information Maintenance
– get time
– set system data (OS parameters)
– get process information (id, time used)
Operating System Services
- Program execution – system capability to load a program into memory and to run it.
- I/O operations - since user programs cannot execute I/O operations directly, the operating system must provide some means to perform I/O.
- File-system manipulation – program capability to read, write, create, and delete files.
- Communications – exchange of information between processes executing either on the same computer or on different systems tied together by a network. Implemented via shared memory or message passing.
- Error detection – ensure correct computing by detecting errors in the CPU and memory hardware, in I/O devices, or in user programs.
- Program execution – system capability to load a program into memory and to run it.
- I/O operations - since user programs cannot execute I/O operations directly, the operating system must provide some means to perform I/O.
- File-system manipulation – program capability to read, write, create, and delete files.
- Communications – exchange of information between processes executing either on the same computer or on different systems tied together by a network. Implemented via shared memory or message passing.
- Error detection – ensure correct computing by detecting errors in the CPU and memory hardware, in I/O devices, or in user programs.
OPERATING SYSTEM STRUCTURE
SYSTEM COMPONENTS
Operating Systems Process management
- In operating systems, process is defined as “A program in execution” [10]. Process can be
considered as an entity that consists of a number of elements, including: identifier, state, priority, program counter, memory pointer, context data, and I/O request. The above information about a process is usually stored in a data structure, typically called process block. Figure 1 shows a simplified process block [10]. Because process management involves scheduling (CPU scheduling, I/O scheduling, and so on), state switching, and resource management, process block is one of the most commonly accessed data type in operating system. Its design directly affects the efficiency of the operating system. As a result, in most operating systems, there is a data object that contains information about all the current active processes. It is called process controller. Figure 2 shows the structure of a process controller [10], which is implemented as a linked-list of process blocks. In order to achieve high efficiency, process controller is usually implemented as a global variable that can be accessed by both the kernel modules and nonkernel modules. For example, any time a new process (task) is created, the module that created this process should be able to access the process controller to add this new process. Therefore, process controller – the data object that controls the current active process – is usually implemented as a category-5 global variable. This means, both the kernel modules and nonkernel modules can access process controller to change its fields and these changes can affect the uses of process controller in kernel modules.
Main Memory Management
- the act of managing computer memory. In its simpler forms, this involves providing ways to allocate portions of memory to programs at their request, and freeing it for reuse when no longer needed. The management of main memory is critical to the computer system.
- tricky compromise between performance (access time) and quantity (available space). We always seek the maximum available memory space but we are rarely prepared to compromise on performance. Memory management must also perform the following functions:
> allow memory sharing (for a multi-threaded system);
> allocate blocks of memory space for different tasks;
> protect the memory spaces used (e.g. prevent a user from changing a task performed by another user);
> optimise the quantity of available memory, specifically via memory expansion systems.
File Management
- A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data.
- The operating system is responsible for the following activities in connections with file management:
> File creation and deletion.
> Directory creation and deletion.
> Support of primitives for manipulating files and directories.
> Mapping files onto secondary storage.
> File backup on stable (nonvolatile) storage media.
INPUT / OUTPUT SYSTEM MANAGEMENT
- The I/O system consists of:
> A buffer-caching system
> A general device-driver interface
> Drivers for specific hardware devices
> A buffer-caching system
> A general device-driver interface
> Drivers for specific hardware devices
Secondary Storage System
- Main memory (primary storage) is volatile and too small to accommodate all data and programs permanently, the computer system must provide secondary storage to back up main memory.
- Modern computer systems use disks as the principle on-line storage medium, for both programs and data.
- The operating system is responsible for the following activities in connection with disk management:
> Free space management
> Storage allocation
> Disk scheduling
> Storage allocation
> Disk scheduling
Protection System
- A mechanism for controlling access by programs, processes, or users to both system and user resources.
- The protection mechanism must:
> distinguish between authorized and unauthorized usage.
> specify the controls to be imposed.
> provide a means of enforcement.
Command Interpreter System
- Many commands are given to the operating system by control statements which deal with:
>process creation and management
>I/O handling
>secondary-storage management
>main-memory management
>file-system access
>protection
>networking