1. GUIDE
MS. ANUPAM SINGH
IT
HPL

2. When two processors
request access to a shared
memory at approximately
the same time, the Arbiter
puts the requests into one
order or the other, granting
access to only one
processor at a time. The
Arbiter guarantees that
there are never two actions
under way at once, just as
the traffic officer prevents
accidents by ensuring that
there are never two cars
passing through the
intersection on a collision
course.
N x M
Arbiter
Client 1
Client N
Resource 1
Resource
M
(Release)
(Available)
(Grant)
(Request)

3. Round-robin (RR) is one of the simplest scheduling
algorithms for processes in an operating system. As the term is
generally used, time slices are assigned to each process in equal
portions and in circular order, handling all processes
without priority (also known as cyclic executive). Round-robin
scheduling is simple, easy to implement, and starvation-free.
RR scheduling algorithm is given by following steps:-
1. The schedular maintains a queue of ready processes and a list of blocked and
swapped out processes.
2. The PCB of newly created process is added to end of ready queue. The PCB
of terminating process is removed from the scheduling data structures.
3. The schedular always selects the PCB at head of the ready queue.
4. When a running process finishes its slice, it is moved to end of ready queue.
5. The event handler perform the following action
a) When a process makes an input -output request or swapped out,its PCB is
removed from ready queue to blocked/swapped out list
b)When input-output operation awaited by a process finishes or process is
swapped in its process control block is removed from blocked/swapped list to end
of ready queue.

4. An arbiter would typically employ a scheduling algorithm to
decide which one on several requestors would be serviced.
The round robin arbitration, in its basic form, is a simple
time slice scheduling, allowing each requestor an equal
share of the time in accessing a memory or a limited
processing resource in a circular order
Round robin arbitration is a scheduling scheme which gives
to each requestor its share of using a common resource for
a limited time or data elements. The basic algorithm
implies that once a requestor has been serves he would “go
around” to the end of the line and be the last to be served
again. The simplest form of round robin arbiter is based on
assignment of a fixed time slot per requestor.

5. R0
R1
R2
R3

6. L =LAST GRANT
L00 L01 L10 L11
00(START) G1(WAS LAST
GRANT )
G2(WAS LAST
GRANT)
G3 (WAS LAST
GRANT)
G2 G3 G1
LOW LOW LOW
LOW LOW ACTIVE
ACTIVE LOW LOW
LOW ACTIVE LOW
G2|G3 G1 |G3

7. •L00 R1 R2
•L01 R2
•L10 R3 R0 R1 R2
•L11 R0 R1 R2
•L00 R1 R2 R3
•L01 R2 R3
•L10 R3
•L11 R0 R1 R2 R3
•L00 R1
•L01 R2 R3 R4 R0
R1
•L10 R3 R0 R1
•L11 R0 R1
•L00 R1 R2 R3 R0
•L01 R2 R3 R0
•L10 R3 R0
•L11 R0
R0
L00(UNMASKING
CASE)
R1 L01
R2 L10
R3 L11