Tagged Questions

Questions about the principles of software that interfaces between hardware and applications.

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0answers
17 views

Why laptop's monitor freezing and becoming inaccessible? [on hold]

I have a Toshiba Satellite L300 with configuration : Intel Pentium Dual Core Processor 2GB RAM 200 GB HDD OS- Windows 7 ( Now there is none, I can't install one now!) Old by more than 6 years 1/2 ...
0
votes
0answers
10 views

Solve a basic mutex lock problem while preventing deadlock

I am solving a problem with a bridge, where you have a one way bridge with people coming from each side. To solve this problem while preventing deadlock (two people going opposite directions on the ...
0
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0answers
16 views

Operating Systems Qualifying Exam Visual Study Aids

I have read the Operating System Concepts book, watched a lot of videos on YouTube, practiced with past qualifying exam questions and several exams from other CS departments around the world. ...
0
votes
1answer
30 views

Operating System Paging concept

I am quoting a paragraph from the book "Operating System Principles" by Galvin. Usually, each page-table entry is 4 bytes long, but that size can vary as well. A 32-bit entry can point to one of ...
0
votes
2answers
50 views

How CPU know which process generated an interrupt?

When a computer OS supports multi-program, it needs to have a scheduling algorithm to handle which process will be run by the cpu. If a process is in state 'blocked' waiting for IO, the scheduling ...
0
votes
1answer
16 views

Round-Robin Scheduler - What exactly is the quantum time used for?

Suppose you have three stages for a job: Creation stage = the job gets created Executing stage = the job is executed/served Finishing stage = the job is "marked" as finished. Now, say the quantum ...
-1
votes
1answer
17 views

Calculating disk seek times

I have a system where disk requests come to a disk drive for cylinders in the order 10, 22, 20, 2, 40, and 38 at a time when the disk drive is reading from cylinder 20. The seek time is 6ms per ...
-1
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0answers
30 views

Calculating availability of a system

Last year, a company providing web application services needed an Internet line to service clients’ demand at that time. However, in order to increase availability, the company actually ...
2
votes
0answers
31 views

Mesa Semantics without Starvation?

When a process inside a monitor with Mesa semantics finishes, another process can acquire the monitor. Now there can be starvation here when there is a thread with a lower priority. Are there ...
0
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1answer
71 views

Are interrupts needed for a computer system to work?

Are interrupts needed for a computer system to work? Could you have a computer system (hardware and software, including the OS) that worked without an interrupt mechanism?
4
votes
1answer
14 views

How are userland programs executed?

Say we have a simple OS with a filesystem, and some programs on that filesystem. How then does a program get executed by the OS? My understanding is that the executable file gets loaded into memory, ...
3
votes
1answer
32 views

Bare Metal Operating Systems in High Performance Computing

Few years back, I stumbled across Return Infinity - the OS framework designed around flat, 64bit memory model, with minimal MMU / VM overhead, etc. I'm wondering if there are any public benchmarks or ...
3
votes
2answers
56 views

Where is the OS when a process is running?

We know that operating system is responsible for handling memory allocation, process management etc. CPU can perform only one task at a time(assuming it to be single core). Suppose an operating ...
5
votes
1answer
18 views

Can multiple tasks in an RTOS share one stack to save memory?

Many small embedded systems have a limited amount of RAM, 10k or less. I know you can run an RTOS on such systems, however, a realistic number of tasks in such a system is very low, mainly because ...
9
votes
2answers
20 views

How does an operating system create entropy for random seeds?

On Linux, the files /dev/random and /dev/urandom files are the blocking and non-blocking (respectively) sources of pseudo-random ...
2
votes
1answer
24 views

How are system calls handled in a virtual machine?

Quoting wikipedia, a system call is: In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services (e.g. ...
8
votes
1answer
19 views

Memory ballooning in the OS

Some hypervisors optimize memory usage using a method that is called ballooning (at least that's what KVM calls it), this method deduplicates memory between VMs and sets common pages to read-only with ...
10
votes
5answers
20 views

Why is the OS design able to reduce power consumption?

I have read that OSes like Android and iOS are somehow optimised to improve battery life. My understanding is that a CPU executes a certain number of operations in a certain time, so I would think ...
1
vote
2answers
8 views

Handling TOCTTOU with system calls

What are some of the best practices when implementing system call functionality for handling/avoiding "Time of check to time of use" (TOCTTOU) security issues?
8
votes
2answers
27 views

What guarantees do “soft” real-time operating systems actually provide

I think I know what a "hard" real-time operating system is. It is an operating system with a scheduler that provides a contract with the application programmer. An application provides a deadline ...
3
votes
1answer
23 views

Which process states exist a multi-processor machine?

In a single-processor architecture, A process might be New, Ready, Running, Blocked and Terminated. Are there any additional states in a multi-processor architecture?
3
votes
1answer
6 views

Relation between Signals and Events

There are POSIX signals (linux man), and various event-based operating systems (such as TinyOS, most seem to be targeted at embedded systems). But the mechanisms seem very similar. Are the terms ...
1
vote
1answer
12 views

Are Time-sharing and multi-tasking operating systems same or different

My question is regarding time-sharing and multi-tasking systems. Time-sharing operating system assigns time slot to each task while multi-tasking OS runs various jobs in parallel. But as I get it, ...
6
votes
1answer
28 views

Writing a multitasking operating system for a processor without MMU

I've been thinking of writing a hobby operating system for some of the ARM processors. There are many popular single-board computers with ARM MPU, so I simply wanted to purchase one of those (choosing ...
8
votes
1answer
22 views

Performance of microkernel vs monolithic kernel

A microkernel implements all drivers as user-space programs, and implements core features like IPC in the kernel itself. A monolithic kernel, however, implements the drivers as a part of the kernel ...
11
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2answers
22 views

What are potential pitfalls with having a minimal kernel that runs managed code?

Suppose I want to build an operating system based on a very small native lower kernel that acts as a managed code interpreter/runtime and a larger upper kernel compiled to a non-native machine ...
9
votes
3answers
33 views

How does the processor find kernel code after an interrupt?

When an interrupt occurs, the processor preempts the current process and calls kernel code to handle the interrupt. How does the processor know where to enter the kernel? I understand that there are ...
18
votes
1answer
20 views

Can an interrupt handler be preempted?

Can a running interrupt handler be pre-empted by another interrupt handler? If this is possible, in which scenarios is this safe, and in which scenarios is it not? If this is not possible, why?
2
votes
1answer
147 views

Practical Page-Replacement Algorithms

Could anyone suggest other page replacement algorithms that are applicable to the real world aside from FIFO, Second Chance (Clock), Enhanced Second Chance and Random?
1
vote
1answer
80 views

What's the difference between Clock and Second Chance Page-Replacement Algorithm?

I know that they both have reference bit, but I only understand the Second Chance but not the Clock Page-Replacement algorithm. could anyone help me understand?
1
vote
2answers
82 views

What is the maximum directly adddressable memory capacity?

This is taken from OPERATING SYSTEMS: INTERNALS AND DESIGN PRINCIPLES by WILLIAM STALLINGS Consider a 32-bit microprocessor composed of 2 fields: first byte contains the opcode and remainder an ...
5
votes
1answer
96 views

Difference between hypervisor and exokernel

An hypervisor (1st type) is a software that creates and run virtual machines, managing guest's operative systems's requests to the hardware. An exokernel is an operative system kernel, that let's ...
0
votes
1answer
47 views

Does a multi cpu system not improve the first come first serve (fcfs) cpu scheduling algorithm?

I created a program that simulates the fcfs scheduling algorithm. First I implemented it for a single core, then modified it for four homogenoues cpus. I compared the results with several datasets, ...
1
vote
2answers
76 views

Why don't hard drives actually delete data?

As far as I understand it, when you delete a file from trash/recycle bin the file isn't actually erased from memory but is instead marked as being okay to be over written. So, my question is as to ...
2
votes
1answer
93 views

How does the OS know the physical address of a process' first memory page?

If I have a program, its instructions are stored on the hard drive. When I double-click the executable the pages of memory for this process must get loaded in to RAM. However, for the pages to get ...
21
votes
7answers
4k views

Does an Operating System inject its own machine code when you open a program?

I'm studying CPU's and I know how it reads a program from the memory and execute its instructions. I also understand that an OS separates programs in processes, and then alternate between each one so ...
3
votes
1answer
88 views

What is the difference between LRU implemented for a cache and for page replacement?

I have read that true LRU page replacement requires significant hardware support, so only approximation of LRU is implemented for page replacement. So I wanted to contrast LRU that is implemented for ...
0
votes
1answer
32 views

Name for almost random memory distribution on the heap

If I had a heap like the following: with blue blocks being occupied memory and white blocks being free memory What is the general name given to the situation illustrated, where the free and ...
0
votes
1answer
50 views

How is heap memory allocated to a process?

I want to better understand how OS provides heap memory to a process. Here by heap memory I mean the memory allocated dynamically, say by call to malloc. When a ...
2
votes
0answers
23 views

How can I talk about priority inversion if it's impossible to specify priority?

In the paper: Leslie Lamport: What It Means for a Concurrent Program to Satisfy a Specification: Why No One Has Specified Priority; ACM Symp Principles of Programming Languages, (POPL-12):78-83, ...
3
votes
1answer
75 views

Are cache contents specific to a process?

Suppose the L1 cache is filled up with data from some process. Now CPU loads another process. Does the new process share cache contents? Or the cache has to be invalidated completely in each context ...
7
votes
0answers
98 views

Can the end-to-end principle be formalized?

In the late 1990s, when I was in graduate school, the paper JH Saltzer; DP Reed; DD Clark: End-to-end arguments in system design. ACM Trans. Comput. Syst. 2(4):277-288, 1984. ...
2
votes
1answer
22 views

Access control matrices: who are the subjects: users or processes?

I'm studying the basics of security in computers. The doubt I have is that the access control matrix is presented as a matrix whose rows are the subjects and the columns are the objects. Also subjects ...
1
vote
1answer
40 views

How can OS schedule disk requests efficiently without knowing the LBN to PBN mapping ?

I learn from the OS schoolbook that the OS has the function that schedule the disk requests with the knowing algorithms such as SSTF, SCAN .. However, the date layout inner disk drives now is very ...
2
votes
1answer
31 views

Filing systems using index blocks

I know that a disadvantage of the index block system is that it can be wasteful of space if the files involved are mostly small in size, as index blocks are allocated from free space as required and ...
0
votes
1answer
65 views

Is the way an OS schedule threads related to parallel computing?

From Wikipedia: Operating systems schedule threads in one of two ways: Preemptive multitasking is generally considered the superior approach, as it allows the operating system to determine ...
0
votes
2answers
214 views

How does an operating system implement the C library?

I have an idea of how a C program is turned into machine code by the compiler. I also know how the processor processes the instructions (https://www.youtube.com/watch?v=cNN_tTXABUA this video has a ...
0
votes
1answer
96 views

How does an Operating System without kernel mode works?

Andrew S. Tanenbaum in his book "Modern Operating Systems 3rd Edition" states that the distinction between operating system software and normal (user mode) software can sometimes be blurred in ...
0
votes
0answers
175 views

size of memory in 64-bit computer system

I'm new here, a brief intro, I'm a student majoring in comp-sci. Right now I'm having a bit confusion to answer one of my assignment, it is about system paging. I want to know how do I able to know ...
3
votes
0answers
53 views

How hardware interrupt works on music

Does music stop for a short interval while listening into it,maybe a milliseconds that we just doesnt sense it cause by interrupts for operating system to run other programs