1. Process management
• Status of the process (★)
• Process synchronization and mutual exclusion (★★★★)
Critical resources: resources that need to be shared between processes in a mutually exclusive manner, such as printers, tape drives, etc.
Critical section: The section of code in each process that accesses critical resources is called the critical section.
Semaphore: is a special variable
Note: P is Passeren in Dutch, and V is Verhoog in Dutch.
• Precursor graph (★★★★)
• Semaphores and PV operations (★★★★)
• Deadlock and Banker’s Algorithm (★)
Process management is the core of the operating system, but if it is not designed properly, deadlock problems will occur. If
a process is waiting for something that cannot happen, the process is deadlocked. And if one or more processes
deadlock, it will cause a system deadlock.
2. Storage management
• Segmented page storage (★★★)
Page storage : Divide the program and memory into blocks of the same size, and transfer the program into the memory in units of pages.
Advantages: high utilization, small fragmentation, simple allocation and management
Disadvantages: Increased system overhead; possible jitter
Segmented storage : The logical space is divided according to the natural segments in the user's job, and then transferred into the memory. The lengths of the segments can be
different.
Advantages: Multi-programs share memory, and modifications of each program do not affect each other.
Disadvantages: Low memory utilization, large waste of memory fragmentation
Segmented page storage : a combination of segmented and paged storage. Segment first, then paginate. A program has several segments, and each
segment can have several pages. The size of each page is the same, but the size of each segment is different.
Advantages: little space waste, easy storage sharing, easy storage protection, and dynamic linking
Disadvantages: Due to the increase of management software, the complexity and overhead also increase, the required hardware and the occupied content
also increase, which greatly reduces the execution speed
• Quick watch
The fast table is a small-capacity associative memory (Associative Memory), which is composed of high-speed caches. It is
fast and can guarantee parallel search by content from the hardware. It is generally used to store the few active pages that are currently most frequently
accessed page number.
Fast table: stores the page table in the Cache; slow table: stores the page table in the memory.
• Page replacement algorithm (★)
• Document management
File Properties
- R Read Only File Properties
• A Archive Properties
• S System Files
- H Hidden Files
• Absolute paths and relative paths (★)
Absolute path: is the path starting from the drive letter.
Relative path: is the path starting from the current directory.
If the current directory is: D1, and the path is required, then: absolute path: /D1/W2/F2, relative path: W2/F2
• Index files (★★★)
• Bitmap (★)
Free area table method (free file directory)
free list method
bitmap
group chaining
3. Job management
device management
• Microkernel operating system
• Embedded operating system
Embedded operating system features:
- miniaturization
- high code quality
- specialization
- Strong real-time
- Tailorable and configurable.
The kernel services of real-time embedded operating systems include: exceptions and interrupts, timers, and I/O management.
Common embedded RTOS (real-time operating system, Real-Time Operating System) VxWorks, RT-Linux, QNX, pSOS