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If the entire image must be in main memory, then the image must be small and only a limited number of processes can be active at anytime. This problem can be solved by using virtual memory, so that only a portion of the process image (the portion currently being used) needs to be in memory atany given time.

It states that unix is unsuitable for real-time applications because a process executing in kernel mode may not be preempted. elaborate.

Because there are circumstances under which a process may not be preempted (i.e., it is executing in kernel mode), it is impossiblefor the operating system to respond rapidly to real-time requirements.

Use the ps program to list all the processes running on a linux machine (including system processes and processes for all users). list oneProcess for each unique state that is listed (i.e. one per unique entry in the state column) and describe what state this process is in. see the manual pageFor help with ps. next, create five new processes in quick succession and leave them running. using ps, list their process identifiers. is there any relationBetween the identifiers they are assigned?

You can use ps ax to list all the processes on a Linux machine. Here is a list of some of the processes I found:

PID TTY STAT TIME COMMAND

1 ? S 0:04 init [3]

2 ? SN 0:00 [ksoftirqd/0]

3 ? S<0:02 [events/0]

4 ? S<0:00 [khelper]

9 ? S<0:00 [kthread]

18 ? S<0:06 [kacpid]

118 ? S<0:00 [kblockd/0]

176 ? S 0:00 [pdflush]

179 ? S<0:00 [aio/0]

178 ? S 0:01 [kswapd0]

771 ? S 0:04 [kseriod]

829 ? S<0:00 [ata/0]

843 ? S<0:00 [reiserfs/0]

983 ? Ss 0:00 /sbin/devfsd /dev

5192 ? S 0:00 [khubd]

6328 ? Ss 0:00 metalog [MASTER]

6332 ? S 0:00 metalog [KERNEL]

6366 ? Ss 0:00 /usr/sbin/acpid -c /etc/acpi/events

6991 ? Ss 0:00 /usr/sbin/cupsd

7326 ? Ss 0:00 /usr/sbin/fcron

7422 ? Ss 0:00 /usr/sbin/speedfreqd -P /var/run/speedfreq.pid -p pow

There are many more. The TTY column indicates whether the process is attached to a termanl, and STAT gives the state of the process.Most processes are sleeping (S), one has been given a low priority (N), and others have been given a high priority (<). Notice that typically important system processes have a high priority.

If you create five processes in quick succession, they will typically have sequential process identifiers.

How is a process switch different from a mode switch?

A process switch involves the operating system having to do a lot of work, whereas a mode switch is done completely in hardware. Amode switch involves saving the state of the current process (in hardware), changing to supervisor mode, then giving control to the operating system. Theidea is that the operating system will execute a short handler, then return control to the processor. The processor will restore the state of the originalprocess and continue.

With a process switch, the operating system must give control of the CPU to a different process, rather than resuming with theprevious process that was running. Thus it must save the context of the current process in its PCB, update the PCB state and accounting information, move thePCB to a new queue, execute the scheduling algorithm to choose a new process,remove the PCB of that process from the ready queue, update its memory management structures, and restore its context into the processor.

Questions & Answers

Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
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Source:  OpenStax, Operating systems. OpenStax CNX. Aug 13, 2009 Download for free at http://cnx.org/content/col10785/1.2
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