Questions: 1. Why single block of memory management method would affect the operating system and applications after changing position?
2, how to determine the frame offset and a size?
3, how do I find files on their computers?
4, the process is not thread?
第十章、操作系统1, the operating system of the computer hardware and software closely linked, it is the basis for other software dependent and allows us to write programs that interact with the machine
2, classification software: Modern software can be divided into two categories: application software and system software. Application software to meet the specific needs - to solve real-world problems in written; System software is responsible for managing computer systems on the base layer, which provides the tools and environment for creating and running software applications. It can interact directly with the hardware.
3, the computer's operating system is the core software, the operating system is responsible for managing computer resources, other system software supports a specific purpose
4, a computer operating system usually only one active, the process of loading ROM provides the user interface is termed to boot the computer. Guide can be, but no matter what, the computer is always controlled by a dual-boot and multi-boot operating system.
5, the operating system's central idea is a good share. The concurrent execution of a plurality of programs shared memory. Executing program resides in main memory.
6, some key operating system concepts: (1), memory management: know how many programs and their position in the main memory contains the action.
(2) the process: during program execution in a dynamic representation
(3), Process Management: Understanding action information of active processes
(4), memory management and process management requires CPU scheduling: determine which process the main memory can access operation of the CPU for execution.
(5), operating: system software or the user needs additional resources required for the execution of the program provides a set of separate instructions, the program instructions are grouped together and called a job
(6), batch: comprising the same or similar resource needs job these jobs are loaded into memory, CPU and other competition the right to use shared resources. Batch does not require interaction between the user and the program.
(7), sharing: sharing system allows multiple users to interact with the computer. Multi-channel programming method allows simultaneous multiple active processes. Sharing system initially consists of a host and a plurality of dumb terminals connected to the host. Dumb terminal: a monitor and keyboard. Dumb terminal may extend over the entire building, and the host is placed in a special room, the operating system resides in the host, all processing occurs here.
(8), the login process; represent each user.
7, other OS features: The operating system is responsible for communication with a variety of bi variety of equipment, such communication is done with the help of device drivers, so-called device drivers, it is to understand the specific device to receive and publish information about the desired adaptations applet mode.
The final element of the operating system is needed to support real-time systems, real-time system: nature of the application determines the response time to always turn off the system. Response time: the time delay between the received signal and generates a response.
8, memory management: operating system software requires the following elements: 1, a tracking program memory resides in what position and how resides. 2, converts the logical address into an actual program memory addresses.
9, logical address: store the value of a reference, a program is referenced with respect to its
physical address: a real address in the main storage device
address bindings: mapping between the logical addresses and physical addresses
when compiling the program, an identifier of reference is converted to logical addresses. When the final program is loaded into memory, each logical address is translated into a corresponding physical address. Logical address in memory so that the program can be moved or loaded each time a different location. Just know the location of a stored program, it can be determined in any physical address corresponding to the logical address.
10, memory management methods:
a monolithic memory management: it is divided into only two parts: the operating system and application programs to be executed, as long as the physical address to be generated by adding the logical address to the physical address of the program is actually in the main memory, this approach is simple, but a lot of waste of CPU time and memory space
Partition memory management: fixed partition method: The main memory is divided into a certain number of partitions, size of the partitions need not be the same, but in the initial operating system boot, their small play is fixed. Job will be loaded partitions a space large enough to accommodate it. OS having an address table, storing the starting address and length of each partition.
Dynamic partitions: a partition will be created as needed program. With the address information is loaded and clear program of change. The starting address of the base register, the length of the partition boundaries are stored in the register. In dynamic partitioning, the continuous blank partition will be merged into a large empty partition.
11, three common partition selection method:
first Match: assign a first program partition enough to accommodate it.
Best match: the minimum allocation to accommodate the program to partition it.
Worst match: allocating the largest able to accommodate the program to partition it. Useful for dynamic allocation in
paged memory management method: it requires tracking allocated memory, but also to resolve the address, but the elimination of the entire process must be loaded into memory as a continuous whole, so that the city no size limit.
The process is divided into fixed-size pages, load the memory management method stored in the frame memory when.
Frame: the size of the fixed portion of the main memory, for storing the process page
page: fixed size part of the process, is stored in the frame memory
page mapping table: operating system tables for the relationship between the recording frames and pages
paged memory management system the distinction between the logical address and the same system, the address is replaced by two values: the page number and offset. Divided by the size of the logical address of the page with the page number quotient is, the remainder is offset. <Page number, offset>, the physical address to be generated, first of all have to view the PMT, multiplied by the frame size of the frame number, adds the offset to
the advantages in the dry tabs do not have to process stored in consecutive memory space network Electricity. This ability to process the segmentation process to find a chunk of free space line reading problem became finding enough to spend more than small memory.
Demand paging: Extended paged memory management method, and only when a page is referenced it will be loaded into memory
Page swapping: put a page, another page will usually removed from memory from secondary storage device loaded into memory
virtual memory: As the whole program does not have to be in memory at the same time caused no program size limitations illusion
thrashing: frequent page processing inefficiencies caused by the exchange
12, process management:
1, process status: enter the system, ready to execute, execute, waiting for resources, the implementation of the end of the
note ready state, the process does not have any obstacles to implementation. There may be more than one process in the ready or wait state, but only one process is running
during operation, the process may be interrupted by the operating system, it is possible for another process to obtain CPU resources, it could be the introduction of a new section to read
13, the process control block: a data structure of the operating system used by the information management processes.
14, the information stored in the PCB:
various kinds of information about the process to
process the values of all of the other CPU registers
to maintain information about the scheduling of CPU
accounting information, such as account, date and time limit for use of CPU time
a context switch: when a process is removed CPU, the register can occur while you replace it with another exchange process
15, CPU scheduling:
non-preemptive scheduling: the currently executing process voluntarily gave up occurs when the CPU scheduling
preemptive scheduling: the operating system decides to take care of another process and seize the currently executing when CPU resources processes.
First come first served and the shortest job first is non-preemptive scheduling. It is the literal meaning of
the polling method: that specifies the time slices, and then follow the order cycle, the end of a project, it has since terminated, then it is no longer involved in the cycle.
Turnover period: the turnover of each process cycle time to complete its
Chapter IX, file systems and directories
1, file systems: the main memory is where programs and data are being used to store activities.
File: famous collection of data used to organize secondary storage device
file system: the operating system provides a logical view of the file he managed
directory: famous grouping file
format Some files are very strict, some file format is flexible
can put files See sequence as a sequence of bytes, the row sequence or record sequence
2, text files and binary files
text files: character file contains
binary file: a file contains the data in a particular format, a specific request to the bit string of explanation
some Offers character representation, sometimes this file is called source
file types: text data files, audio files, image files, word processing documents, programmer file
filename is usually divided into two parts by a dot, that is the main file name and file extension. File extension describes the type of file, told Open your file. Change the file extension does not change the data file or its internal format.
3, file operations:
under the assistance of the operating system:
create file
delete a file
open file
close the file, read data from a file, the file data is written, the current file pointer in the file relocation, the additional data to the end of the file, delete files, rename files, copy the file
to read file: refers to a copy of the documents submitted by the operating system starting from the current file pointer to the data. After the read operation occurs, the file pointer is updated, the write information is the data stored in the position indicated by the current file pointer points, and then update the file pointer
Delete: Deletes the contents of the file, but does not delete management entry in the file table
4 , file access: access to the file type is set when the file was created
File access method defines a process of relocation of the current file pointer, which the physical device with limited storage file independent
5, two methods of file access:
sequential file access: linear method to access data files
direct file access : the method specified by the logical record number to directly access the data file
6, file protection: file protection is provided with three categories: OWNER, GROUP, WORLD
OWNER writable, GROUP-readable, world can not read
7, directories: directory storing the file name, the current size of the file type, address, and files stored on the hard disk, in addition to the directory information is also stored in the file protection settings, as well as when a file was last modified and when created
Once a directory file, it must support the general operation of the directory files.
8, the directory tree:
presentation files nested directory structure of the organization
root directory: the directory that contains the highest of all other directories, a bit like a tree structure
9, the working directory: a subdirectory of the current activities of
10, path: Word file or directory in the file system text the name of the location of the
absolute path: starting from the root directory, subdirectory contains the path to all subsequent
relative path: a path from the current working directory.
When using a relative path: sometimes you need to return to the upper directory, use absolute paths will not pay attention to such cases.
.. represents the parent directory
11, disk scheduling: decided to meet the disk I / O operation requested
12, first come first served disk scheduling
shortest seek time disk scheduling priority method
SCAN disk scheduling method