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53 Cards in this Set

  • Front
  • Back

What is the OS?

the interface between the hardware and software

What are the modes of the OS?

User Mode

Kernel Mode

What is user mode?

Programs use this mode, it is a protected mode so user programs cannot damage resources or make them unusable

What is kernel mode?

The mode the OS uses to interact with the processor

Wat was the purpose of the monitor?

- User no longer has direct access to processor

- Controls the sequence of events

- Resident monitor is software always in memory

- Reads in job and gives control

- Job returns control to monitor

What is the degree of multi programming?

The number of programs that can be resident in main memory at the same time.

- in modern systems, if memory is full, it swaps data to hard disk that is waiting for something that is ready to run.

What is a heavy computer?

Processor intensive

What is uni-programming?

Sequential operation, one after the other

What is batch multi-programming system?

- Earliest systems

-Main focus was to accept jobs from user, schedule them and then execute them

- Main goal was to improve throughput

- Maximize # of jobs completed

-Totally automated, gets job from file, returns to file

What is a time shared multi-programming sytem?

- User interaction, not automated

- Main goal was response time (the avg time it takes to get a response for a command)

What was the purpose of the monitor?

Memory protection

- stop access to kernel or another users memory

How do you protect memory?

The kernel turns to user mode before turning control over to users program to run, when control is handed back it goes back into kernel mode.

What is a process?

A program in execution

When you want to run a program what must happen?

It must be brought into main memory, when it is executed it becomes a process.

What are the 3 components of a process?

1. An executable program(code)

2. Associated data(variables and constant's)

3. Execution context (values in the registers when program is interrupted)

What is a race condition?

When the output is different depending on the order of the programs running.

- A program should not should not depend upon another, should be the same no matter the order in which they are executed.

What is a deadlock?

A program 1 is waiting on program 2 at the same time program 2 is waiting on program 1.

What is mutual exclusion?

Making sure 2 programs do not try to modify a shared resource at the same time.

- Non shareable resources must be assigned to one process only.

What is synchronization?

blocking a program until a particular event occurs

What are the keys to virtual memory?

-Programs loading is on demand(only when needed)

- It generates a logical address (page # followed by offset)

What is the job of the main memory management unit MMU?

When a program requests a page, it loads it

-keeps a table of pages(page table for each program)

What is process scheduling?

Decides which job to run next

- OS uses queue's to do this

What is a Micro-kernel?

- A very small kernel

- Only essential function in the kernel mode

- Rest are kept in user mode

- Much easier to test

What is a Monolithic kernel?

- bundles everything into one program

- More difficult to test

- Very large , 10's of thousands lines of code

How do threads compare to processes?

thread is a very light weight process, threads can be part of a process, and a process can have many threads that share the data of the process.

What is in the short-term queue?

processes that are ready to run

What is in the long-term queue?

Processes waiting for I/O data requested to arrive

What is in the I/O queue?

used when multiple processes are requesting the services of a I/O device, this is handled by the OS

What are the keys to the Monolithic-kernel architecture

- non paging

- One big piece of code

- cannot be interrupted

- simplifies implementation

What is multi-threading?

- divided into threads that can run concurrently

What is a thread ?

- dispensable unit of work

- includes a processor context and its own data are to enable subroutine branching

-executes sequentially and is interruptible

What is Symmetric Multiprocessing (SMP)?

- term refers to computer hardware architecture

- several processes can run in parallel

- all processors can perform the same functions

- processors share same main memory and I/O facilities

What are the benefits to SMP?

-Performance, more than one process can be run at the same time

- Availability, Failure of a single processor does not halt the system

- Incremental growth, can add more processors to improve performance

- Scale-ability, allows room for growth of system without needing to redesign

What are the benefits of distributed Operating systems?

- A single main memory space

- Single secondary memory space

- unified access to facilities

What are the benefits of Object Oriented design?

- Used for adding modular extensions to a small kernel

- Enables programmers to customize a OS without disrupting system integrity

-Eases development of distributed tools and OS systems

What is fault tolerance?

The ability of a system of component to continue normal operation despite the presence of hardware or software faults

- typically involves some degree of redundancy

What is reliability?

the probability of correct operation up to a time given the system was operating correctly

What is mean time to failure MTTF?

Average time that the system runs without failures

What is mean time to repair MTTR?

the average time it takes to repair the system and bring it back online

What is the definition of availability?

defined as the fraction of time the system is available to service users requests

What is the key responsibility of an OS?

Managing resources

- efficiency

- fairness

- differential responsiveness

What are the basic measures of a system?

- Reliability

- Mean time to failure MTTF

- Mean time to repair MTTR

- Availability

What are the types of Fault categories?

Permanent (after occurs it is always present)

Temporary (not always present)

Transient (only happens once)

Intermittent (happens multiple times and is unpredictable)

What are some of the ways to incorporate fault tolerance into a OS?

- process isolation

- concurrency

-virtual machines

checkpoints and rollbacks

How does interrupt affect fetch-execute cycle?

The processor is not waiting on the slower I/O devices. It can move on to next process and goes back using the interrupt when the process is ready.

What is the role of IR (Instruction register) in fetch-execute cycle?

Holds the address of the current instruction being executed.

What is the use of MAR/MDR(or MBR) in fetch-execute cycle?

1. MAR sends instruction to memory

2. memory returns address to MBR/MDR

3. MBR/MDR sends address to the IR

What is the locality of reference principle and how is it used to enhance the performance of a computer system?

The principle of what the SRAM will store.

1. Data the CPU may need again

2. Adjacent data to CPU may need

Why was memory protection needed in monitor based systems?

To prevent and protect users memory area from other users.

What is the main advantage of interrupt driven I/O ?

I/O devices are much slower than the processor, so using interrupts allows the processor to do other tasks without having to wait on slower devices.

What are 3 design considerations for cache system design?

-size of cache

-size of the block to retrieve

-mapping scheme

What is the job of the memory management unit?

- process isolation, automatic allocation and management to support modular programming

- It stores address in a table so it can use virtual memory and find data quickly

What action is taken by MMU when requested page is not found?

It retrieves the block from the disk that contains what is needed and adds entry into the table in allowing for dynamic mapping between virtual address using in programs and address in main memory