Kernel RTOS Development Interview Questions

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by Ruchitha Geebu
Last modified: March 18th 2021

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Best RTOS Interview questions

Q1. In RTOS having 1okbytes of memory and your program for asking for 5kbytes and you got null error? why does it behaves like this?

Ans: RTOS might be having 10k memory, might not fragmentation problem, and the largest hole available to user might be lesser than 5k, this condition might be one of the reason for NULL error.

Q2. What is the need of creating 4GB of pages in Linux?

Ans: Well, the simple answer is it can address so much of memory with available 32 address lines. 2 ^ 32 = 4 GB.

Q3. What are the rules you follow when you are writing critical section of code?


a)Use Atomic Instructions

b) Remember to enable interrupts

c) Make the critical section code as small as possible. (Prefer not more than 20 instructions)

d) Prefer not to call other functions from the critical 

if u r calling, see that there is no critical  section in the other function too. Critical section is  bounded by Disable Interrupt and Enable Interrupt.

Check the example below.


/* Critical Section Start */
Some Instructions A ….
Call FnB();
/* do Something B */
Some Instructions B ….
/* Critical Section End */

/* Critical Section Start */
Some Instructions .. 
/* Critical Section End */

Now the Enable_Interrupts in fnB() will enable the  interrupts and hence “Some Instructions B ..” in fnA()  which should have been in critical section will no more be  in critical section because the interrupts are already  enabled!!
Please check if this condition is handled by the Enable and  Disable functions. If you want suggestions on how to solve  this problem, do revert back

Q4. What are the advantages and disadvantages of winCE compared to GPOS?



1) Supports various types of processor platforms

2) Possible to Customize the Kernel and can reduce its size (upto ~300KB kernel size)

3) Especially for the embedded device platforms


1) Process limits, max. 32 process at a time in WinCE 5.0

2) Limited space allocation for each processes, 32MB/each process

Q5.  Why MFC is not Supporting in Smartphones,This is also winCE mobile then why?

Ans: Well there is nothing to related with limited H/w I believe, Because MFC is just a collection classes designed using the Windows APIs , to provide ease of use.  So the proper answer may Be… To design any application on mobile.. We have very limited APIs which user can directly used. Generally in Embedded system (even in Soft RTOS also ) , if application design using less ( comfort )layer like MFC ( and other if it is there :) ),then your aplication would be more efficient. That’s why even today’s era… The application written in Assembly is the most efficient application then others.

Q6.  What is the difference between winCE4.0 and winCE5.0 Is there any specialty?

Ans: Speciality in the sense …

1) number of processes supported by wince 5.0 is more  than wince 4.0

2) memory mapping might be varying.

Q7.  What are the levels in winCE architecture?

Ans: There are four levels in Win CE architecture.

They are 

1)Hardware layer

2)OEM layer

3)OS layer

4)Application layer

Q8.  What are the SDKs developed by winCE?

Ans: MSFT standard SDK’s are,

1. Windows Mobile for Smartphone = Windows Mobile Standard.

2. Windows Mobile for Pocket PC = Windows Mobile Classic.

3. Windows Mobile for Pocket PC Phone Edition = Windows Mobile Professional.

Q9.  What is the difference between normal OS and winCE OS?

Ans: Normal OS wince 

drivers runs under User space(part of device manager)

kernel space

cannot be customized customized for embedded application

for embedded application like mobile phones,thin client…

(exception linux)

kernel – monolithic kernel- micro kernel

Q10. What is CE Stands in winCCE?

Ans: In the name “Windows CE,” the letters “CE” are not an  abbreviation for anything, but rather they imply a number  of the precepts around which Windows CE is designed,  including “Compact,” Connectable,”  Compatible,” “Companion,” and “Efficient.”