- Operating system must be made available to hardware so hardware can start it
- Firmware used to hold initial boot code
- Operating systems are designed to run on any of a class of machines; the system must be configured for each specific computer site
- SYSGEN program obtains information concerning the specific configuration of the hardware system
- Booting – starting a computer by loading the kernel
- Bootstrap program – code stored in ROM that is able to locate the kernel, load it into memory, and start its execution
JAVA VIRTUAL MACHINE
- Compiled Java programs are platform-neutral bytecodes executed by a Java Virtual Machine (JVM)
- JVM consists of
- Just-In-Time (JIT) compilers increase performance
Simple Structure
-->View the OS as a series of levels
-->Each level performs a related subset of functions
-->Each level relies on the next lower level to perform more primitive functions
-->This decomposes a problem into a number of more manageable subproblems
Layered Approach
The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.
With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers.
<--MS-DOS Layered Structure-->
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.
Additional functions exist not for helping the user, but rather for ensuring efficient system operations.
•Resource allocation – allocating resources to multiple users or multiple jobs running at the same time.
•Preemptable, nonpreemptable resources
•Deadlock prevention and detection models
•Accounting – keep track of and record which users use how much and what kinds of computer resources for account billing or for accumulating usage statistics.
•Protection – ensuring that all access to system resources is controlled.
SYSTEM COMPONENT
Operating Systems Process Management
A process is a program in execution. A process needs certain resources: CPU time, memory (address space), files, and I/O devices, to accomplish its task.
The operating system is responsible for the following activities in connection with process management.
-->Process creation and deletion.
-->Process suspension and resumption.
-->Provision of mechanisms for:
-->Process synchronization
-->Process communication
Main Memory Management
Memory is a large array of words or bytes, each with its own address. It is a repository of instructions and data shared by the CPU and I/O devices. Main memory is a volatile storage device. It loses its contents in the case of system failure.
The operating system is responsible for the following activities in connections with memory management:
-->Decide which processes to load when memory space becomes available.
-->Allocate and deallocate memory space as needed. Keep track of which parts of memory are currently being used and by whom.
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.
Before mounting,
-->Files on floppy are inaccessible
After mounting floppy on b,
-->Ffiles on floppy are part of file hierarchy
I/O System Management
The I/O system consists of:
-->A buffer-caching system
-->A general device-driver interface
-->Drivers for specific hardware devices
Secondary Storage Management
Since 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.
Most 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
Protection System
Protection refers to 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
Command-Interpreter reads commands from the user or from a file of commandsand executes them, usually by turning them into one or more systemcalls. It is usually not part of the kernel since the command interpreteris subject to changes.
The program that reads and interprets control statements is called variously:
-->command-line interpreter
-->shell (in UNIX)
Its function is to get and execute the next command statement
