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operating-systems interview questions

Top operating-systems frequently asked interview questions

Does every OS need RAM?

Is there an OS which can be used without RAM, specifically the kind I can create a bootable pendrive from and use it in the computer? This gets awkward, since booting is essentially loading OS in RAM.

Note: I originally wanted to know about a RAM-less OS to check if my laptop (which does not boot but presents a blank screen) RAM had gone bad, but I like the way this question has snowballed.


Source: (StackOverflow)

Do 64bit software/applications require more RAM than their 32bit counterparts?

I just saw these minimum requirements for a game:

Memory: 2GB for 32-bit OS or 4GB for 64-bit OS

Why does the 64bit OS require more RAM than its 32bit counterpart?


Source: (StackOverflow)

What does an operating system look like without a shell?

A shell like the bash or command.com (up to Windows ME) or CMD.EXE (in later versions) provides an interface that (among other things) accepts commands from the user. What does an operating system look like before a shell is run? How were systems used before the first shell was developed (e.g. UNIX in the early 1970s)? If a computer cannot even accept commands (there is no command line), how can a user interact with it? What is this most basic interface? Can I run this interface in a terminal emulator or is there no way going behind a shell?


Source: (StackOverflow)

What is there in an Operating System other than the kernel

As I understand it, the kernel does all the interaction with the hardware, and manages the memory, the I/O devices, etc. So the kernel is doing everything, yet it is just a part of the operating system. So what else is there in an OS ? Just the applications that come bundled with it ? For example, what does Ubuntu have other than a kernel ? The Gnome Desktop, and a few other applications ?


Source: (StackOverflow)

Does Windows still rely on MS-DOS?

I am just about to start an OS course and as an Apple user I am not very familiar with the underlying details of Windows OS. I was wondering, is MS DOS still used with Windows running on top or is ONLY Windows used now as the OS? I was a little confused because I read somewhere that MS-DOS is used for booting but Windows has all other OS capabilities built into it and thus is used for all other OS operations...


Source: (StackOverflow)

Use physical harddisk in Virtual Box

Using Virtual Box, how can I install an OS to a secondary, physical disk, and boot it in both (at separate times) Virtual Box, and as a typical secondary OS install?


Source: (StackOverflow)

Should I install 64-bit versions of operating systems?

With the release of Windows 7 coming up, 64-bit operating systems have caught my attention.

What are the main advantages and disadvantages of installing 64-bit Windows 7? What type of compatibility issues will I face and would i have to install 64-bit software, or will all the applications I have been using in 32-bit operating systems work just the same?

Edit: My computer is only 5 months old, so it supports 64-bit operating systems


Source: (StackOverflow)

What are the functions of the BIOS while the operating system is running?

I always wondered whether the BIOS (apart from conducting POST, starting the bootloader and passing control to the OS after one presses the power button) has any purpose or function while the operating system is running?

Does the operating system communicate with the BIOS while running and if so, how?


Source: (StackOverflow)

How does the computer know that the PC was not properly shut down?

Actually, this question struck me because of power cuts in my house. When there is a power cut, there is a sudden loss of power from the computer.

How does the computer know that the shutdown was not properly done?


Source: (StackOverflow)

cat /proc/meminfo what do all those numbers mean

In reading the man page on the free command in Linux. I found that is gets its info from /proc/meminfo.

I understand a few of the entries, like MemTotal and MemFree. What do the rest mean.

cat /proc/meminfo 
MemTotal:        3973736 kB
MemFree:          431064 kB
Buffers:           46604 kB
Cached:           494648 kB
SwapCached:        11360 kB
Active:          2322760 kB
Inactive:         933028 kB
Active(anon):    2057952 kB
Inactive(anon):   679956 kB
Active(file):     264808 kB
Inactive(file):   253072 kB
Unevictable:          16 kB
Mlocked:              16 kB
SwapTotal:       4096568 kB
SwapFree:        3961748 kB
Dirty:               236 kB
Writeback:             0 kB
AnonPages:       2704520 kB
Mapped:           182240 kB
Shmem:             23372 kB
Slab:              93848 kB
SReclaimable:      52044 kB
SUnreclaim:        41804 kB
KernelStack:        5064 kB
PageTables:        64928 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:     6083436 kB
Committed_AS:    7327800 kB
VmallocTotal:   34359738367 kB
VmallocUsed:      321156 kB
VmallocChunk:   34359411708 kB
HardwareCorrupted:     0 kB
AnonHugePages:         0 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:      225280 kB
DirectMap2M:     3895296 kB

Source: (StackOverflow)

Overriding HOMEDRIVE and HOMEPATH as a Windows 7 user

My employer has an Active Directory group policy which sets my Windows 7 laptop HOMEDRIVE to "M:" (a mapped network drive) and my HOMEPATH to "\". Since I have read-only permissions for the root of that shared drive, I cannot create files or directories in my windows home directory. My attempts to work with the IT department have been unsuccessful.

Is there a way for me to globally change these envars at boot or login time? I need for all applications to use alternate values (such as "C:" and "\Users\myname"). I have some installed utilities (like gvim and others) that store preference files in the user's home directory.

IMPORTANT: Changing these envars under "System Properties > Environment Variables" does not work. I have tried setting these as both User and System Variables (including a reboot). TypingSET HOMEin a DOS window clearly shows that my settings are ignored. Also, using "Start in" in a Windows shortcut will also not solve this, as I need things like Explorer context menu items (like "Edit with Vim") to operate correctly.

I do have admin rights on this company laptop, but I am not a Win7 guru. Back in the day, a boot script would have solved this in a minute. Is it even possible today? Thanks.


Source: (StackOverflow)

How computers display raw, low-level text and graphics

My ever-growing interest in computers is making me ask deeper questions, that we don't seem to have to ask anymore. Our computers, at boot, as far as I understand it, are in text mode, in which a character can be displayed using the software interrupt 0x10 when AH=0x0e. We've all seen the famous booting font that always looks the same, regardless of what computer is booting.

So, how on earth do computers output graphics at the lowest level, say, below the OS? And also, surely graphics aren't outputted a pixel at a time using software interrupts, as that sounds very slow?

Is there a standard that defines basic outputting of vertices, polygons, fonts, etc. (below OpenGL for example, which OpenGL might use)? What makes me ask is why OS' can often be fine without official drivers installed; how do they do that?

Apologies if my assumptions are incorrect. I would be very grateful for elaboration on these topics!


Source: (StackOverflow)

Before Operating systems, What concept was used to make them work? [closed]

The Operating systems have been tightly related to the computer architecture.An OS takes care for all input and output in a computer system. It manages users, processes, memory management, printing, telecommunication, networking etc.It sends data to a disk, the printer, the screen and other peripherals connected to the computer.

Prior to the introduction of Operating System,

What was used in computer systems to make them work?

Which concept was used to operating system in our evolution of computer?


Source: (StackOverflow)

Is it still necessary to shut down computers?

Nowadays with our modern operating systems, is it necessary to fully shutdown computers instead of choosing to stand-by or hibernate computers (desktops and laptops)?

Would there be any side-effects of keeping a computer running continuously without a shutdown (putting it to sleep or hibernating it when it is not used)? For example, hard drive life decrease, system internals (Processors, RAM etc.) aging faster than usual, etc?


Source: (StackOverflow)

Using UDF on a USB flash drive

After failing to copy a file bigger than 4G to my 8G USB flash drive, I formatted it as ext3. While this is working fine for me so far, it will cause problems if I want to use it to copy files to someone which does not use Linux.

I am thinking of formatting it as UDF instead, which I hope would allow it to be read (and possibly even written) on the three most popular operating systems (Windows, MacOS, and Linux), without having to install any extra drivers. However, from what I found on the web already, there seem to be several small gotchas related to which parameters are used to create the filesystem, which can reduce the compability (but most of the pages I found are about optical media, not USB flash drives).

I would like to know:

  • Which utility should I use to create the filesystem? (So far I have found mkudffs and genisoimage, and mkudffs seems the best option.)
  • Which parameters should I use with the chosen utility for maximum compability?
  • How compatible with the most common versions of these three operating systems UDF actually is?
  • Is using UDF actually the best idea? Is there another filesystem which would have better compatibility, with no problematic restrictions like the FAT32 4G file size limit, and without having to install special drivers in every single computer which touches it?

Source: (StackOverflow)