Operating Systems
Terms
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- Direct Memory Access Structure
- Allows high-speed I/O devices to transfer data from buffer storage directly to main memory w/o CPU intervention. Only one interrupt is generated per block instead of per byte. This is much more efficient.
- How do you handle interrupts?
- The operating system preserves the state of the CPU by storing registers and the program counter Determines which type of interrupt has occurred: polling vectored interrupt system Separate segments of code determine what action should be taken for each type of interrupt
- what are the functions of an interrupt
- Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines Interrupt architecture must save the address of the interrupted instruction Incoming interrupts are disabled while another interrupt is being processed to prevent a lost interrupt A trap is a software-generated interrupt caused either by an error or a user request An operating system is interrupt driven
- what is an interrupt
- a way for a piece of hardware (device controller) to inform the CPU that it has finished it's operation usually through the system bus
- what is an operating system
- a program that acts as an intermediary between an user of the computer and the computer hardware
- what are the 4 components of an os
- hardware, os, application programs, users
- What is a bootstrap program?
- is loaded at power-up or reboot Typically stored in ROM or EPROM, generally known as firmware Initializes all aspects of system Loads operating system kernel and starts execution
- Caching
- Important principle, performed at many levels in a computer (in hardware, operating system, software) Information in use copied from slower to faster storage temporarily Faster storage (cache) checked first to determine if information is there If it is, information used directly from the cache (fast) If not, data copied to cache and used there
- Clustering
- a cluster system is like multiprocessor systems, but multiple systems working together, usually sharing storage via a storage-area network (SAN)
- Symmetric clustering
- has multiple nodes running apps, monitoring each other
- Asymmetric clustering
- assymetric clustering has one machine in hot-standby mode meaning that if the active server fails, it becomes the active server
- Timesharing or Multitasking
- logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing. response time should be < 1 sec and each user has at least one program executing in memory
- what is user mode and what is kernel mode
- kernel mode is when a user application requests a service from the os it must transition from user to kernel mode to fufill the request. when the system is executing on behalf of an user application the system is in user mode.