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The four core files
that make up DOS The three basic files are MSDOS.SYS, IO.SYS and COMMAND.COM (if it is PC-DOS, it is IBMDOS.COM, IBMBIO.COM and COMMAND.COM ).Among them, MSDOS.SYS is called the DOS kernel (it can be seen that MSDOS.SYS is a very important file). It is mainly used to manage and start up the various hundred components of the system, making preparations for the DOS boot.
IO.SYS (IO is the abbreviation of Input & Output, which means "input and output") is mainly responsible for the basic input and output of the system, that is, the connection between DOS and various components.
The COMMAND.COM file (COMMAND means "command") is the interface between DOS and the user. It mainly provides some internal commands of DOS, and can accept, discriminate and execute the commands entered by the user. Whether the disk has the ability to start DOS depends on whether it has these three files. The disk with these three files is called the boot disk. In addition, the disk that contains many DOS external commands is called the system disk.
The last thing to note is that the storage locations of the two files MSDOS.SYS and IO.SYS are limited, they must be at the forefront of the physical location of the disk, otherwise they will lose the ability to boot.
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The PC-DOS system call number is int 21h
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The appearance of time-sharing operating system and multi-programming marks the formal formation of this operating system
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The characteristics of multi-channel programming are: multi-channel , macro-parallel , micro-series .
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In the UNIX system, the process is composed of the following three parts : ① process control block PCB; ② data segment; ③ text segment.
In order to save the memory space occupied by the process control block, the UNIX system divides each process control block into two parts. A part of the resident memory PROC , regardless of whether the process is occupying the processor or not, the system often queries and processes this part of the content. The resident part includes: process status, priority number, process characteristics, data segment start address, waiting reason and Queue pointers, etc., are some of the main information that must be used when performing processor scheduling. The other part is non-resident memory USER . When the process does not occupy the processor, the system will not query and process this part of the content, so this part of the content can be stored in the swap area of the disk, it changes with the user's program and data part In or out of memory.
The UNIX system divides the process data segment into three parts: the user stack area (information area for user programs); user data area (including user work data and non-reentrant program segments); system data area (including system Variables and swap information).
The text segment is a reentrant program that can be shared by several processes. In order to manage shareable text segments, UNIX sets up a text table, each text segment occupies an entry, used to indicate the location of the text segment in memory and disk, the size of the segment, and the number of processes that call the segment Etc.
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Original link: https://blog.csdn.net/SYP35/article/details/48877027
