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Application software, operating software, system call,kernel

 
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Dr.Disrespect
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PostPosted: Sun Dec 30, 2018 12:48 pm    Post subject: Application software, operating software, system call,kernel Reply with quote

I am trying to figure out the interaction between application software, such as Office, games, CE, etc, and operating software. I do not have a computer science background.

I have done some research on the internet. It seems to me that:

1) Because of the limited availability of system resources on a computer, such as CPU time, memory, operating system needs to allocation those limited resources to different application software when they are running simultaneously.

2) Application software communicate with system software like Windows through system calls.

3) Kernel is part of the operating system. It controls the hardware based on the request of application software.

Are these understandings correctly? Thanks.

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OldCheatEngineUser
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PostPosted: Sun Dec 30, 2018 1:26 pm    Post subject: Reply with quote

well, there is much more.
and its hard to count and write every possible relation and/or how things work, however what said is true and false.

processor in real-mode is different than protected-mode, and available features and capabilities change as well.

1. falls short, maybe you need to explain what you meant here?

2. not really, thru APIs and then APIs thru intxx(realmode) sysenter(protectedmode) syscall(longmode)
note: some OS's does not provide api's at all, but they provide interrupts to use.

3. yes, but not really on programs demand. (talking about windows os and window based programs, there are couple restrictions and limitations for programs whether its running in user space or kernel space)

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Dr.Disrespect
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PostPosted: Sun Dec 30, 2018 1:47 pm    Post subject: Reply with quote

OldCheatEngineUser wrote:
well, there is much more.
and its hard to count and write every possible relation and/or how things work, however what said is true and false.

processor in real-mode is different than protected-mode, and available features and capabilities change as well.

1. falls short, maybe you need to explain what you meant here?

2. not really, thru APIs and then APIs thru intxx(realmode) sysenter(protectedmode) syscall(longmode)
note: some OS's does not provide api's at all, but they provide interrupts to use.

3. yes, but not really on programs demand. (talking about windows os and window based programs, there are couple restrictions and limitations for programs whether its running in user space or kernel space)


Thanks for the reply. I should summarize my questions as follows:

1. Why do we need operating systems, such as windows, macOS, etc? What are they used for?

2. What is system call?

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OldCheatEngineUser
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PostPosted: Sun Dec 30, 2018 2:00 pm    Post subject: Reply with quote

1. because not every programmer can setup and configure the hardware and if there is no operating system then every hardware will run one software only, operating systems such as windows, linux or mac are pretty much general purpose operating systems there are some other special type/case operating systems that are built for specific use such as government or military.

2. system call is a high level interrupt used in modern operating systems which is faster than the old one, it generates a signal into interrupt table/handler and the operating system processes that interrupt so you can think of it as a signal to run special operating system function.

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Dr.Disrespect
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PostPosted: Sun Dec 30, 2018 2:28 pm    Post subject: Reply with quote

OldCheatEngineUser wrote:
1. because not every programmer can setup and configure the hardware and if there is no operating system then every hardware will run one software only, operating systems such as windows, linux or mac are pretty much general purpose operating systems there are some other special type/case operating systems that are built for specific use such as government or military.

2. system call is a high level interrupt used in modern operating systems which is faster than the old one, it generates a signal into interrupt table/handler and the operating system processes that interrupt so you can think of it as a signal to run special operating system function.


Thanks for the reply.

1. By stating "setup and configure the hardware", what do you mean? Can you give me a simple example?

2. https://www.geeksforgeeks.org/operating-system-introduction-system-call/ Is the information in this link helpful or correct?

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PostPosted: Sun Dec 30, 2018 2:46 pm    Post subject: Reply with quote

1. when the power or reset button is hit and after POST bios search for any boot-able device and loads the first 512 byte and transfer the control to that loaded code, the initial state of the processor when it wakes up is real-mode and all registers are initialized to 0, most (if not all) features are disabled.
so its part of the operating system to setup (for example) protected mode everytime the system boots up, sets paging, loads global descriptor table, setup segments, locate devices, load other code from hard-drive, setup the screen, monitor ports, graphics, and ... etc.

if we will say we have cheat engine, and we want to run it on an empty-hardware (with no OS) then we have to do all these, and locate the hard-drive to store the boot-able image there and all the required code. including debugging features.

and you have to use IN/OUT port instructions to write bytes, but how could i identify the hard-drive and whats the port number?

or how could i even manage cpu threads and cores?

so yes, any software that can manage all these called operating system. (just wonder how many years microsoft work under constant development to create a beautiful OS such as windows 7 - from 1980s til 2009)

2. correct, but thats not everything.

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Dr.Disrespect
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PostPosted: Sun Dec 30, 2018 5:45 pm    Post subject: Reply with quote

OldCheatEngineUser wrote:
1. when the power or reset button is hit and after POST bios search for any boot-able device and loads the first 512 byte and transfer the control to that loaded code, the initial state of the processor when it wakes up is real-mode and all registers are initialized to 0, most (if not all) features are disabled.
so its part of the operating system to setup (for example) protected mode everytime the system boots up, sets paging, loads global descriptor table, setup segments, locate devices, load other code from hard-drive, setup the screen, monitor ports, graphics, and ... etc.

if we will say we have cheat engine, and we want to run it on an empty-hardware (with no OS) then we have to do all these, and locate the hard-drive to store the boot-able image there and all the required code. including debugging features.

and you have to use IN/OUT port instructions to write bytes, but how could i identify the hard-drive and whats the port number?

or how could i even manage cpu threads and cores?

so yes, any software that can manage all these called operating system. (just wonder how many years microsoft work under constant development to create a beautiful OS such as windows 7 - from 1980s til 2009)

2. correct, but thats not everything.


Thank you very much, that helped a lot! I will give you rep when I can.

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