Dual mode operations in operating systems involve two modes: user mode and system mode (kernel mode), where user mode corresponds to a bit value of 1 and system mode to 0. User mode allows applications to run while system mode provides hardware protection and execution of privileged instructions. Transitions between these modes occur during system calls or exceptions, facilitating requests from user applications.

1. Dual Mode Operations in OS:
User Mode, System Mode &
Kernel Transitions

2. DUAL MODE OPERATIONS
DUAL MODE IS AN
OPERATION OF AN
OPERATING SYSTEM. IT HAS
TWO MODES.
USER MODE AND SYSTEM
MODE (ALSO KNOWN AS
KERNEL MODE, SUPERVISER
MODE, PRIVILÈGE MODE).
THESE MODE ASSIGN WITH
A BIT (0, 1). 1 BIT IS USED
FOR USER MODE AND 0 BIT
USED FOR SYSTEM MODE.
DUAL MODE OPERATION IS
BASICALLY USED FOR
HARDWARE PROTECTION OF
COMPUTER.

3. USER MODE
•When the computer system run user
application like creating a text document
or using an application program. Then the
system is in user mode.
•When the user application requests for a
service from the operating system or an
interrupt occurs, then there will be a
transition from user to kernel mode to
fulfill the requests.

4. SYSTEM MODE
When system boots then hardware starts in System
mode and when operating system is loaded then it start
user application in user mode.
To provide protection to the hardware, we have
privileged instructions which execute only in System
mode.
If user attempt to run privileged instruction in user
mode, then it will treat instruction as illegal and traps to
OS.

5. TRANSITION FROM USER
TO KERNEL MODE
Typically, there are 2 points of switching from user
to kernel mode:
• When calling a System Call
• When an exception comes
To switch from user mode to kernel mode, mode-
bit should be 0 and To switch from kernel mode to
user mode, mode-bit should be 1.

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