Answer :
If a system appears to be having issues with performance for read and write operations to a hard disk, option d. tester is not a valid scheduling method that you could try to improve performance.
Tester is an electric instrument that is employed to see the flow of electrical current is named tester. it's hooked up to the terminals of the electrical circuit. If the bulb of tester glows, it confirms that electrical phenomenon is flowing through the circuit.
Hard disk, conjointly referred to as magnetic disk drive or disc drive, magnetic storage medium medium for a laptop. arduous disks square measure flat circular plates product of metal or glass and coated with a magnetic material. arduous disks for private computers will store terabytes (trillions of bytes) of data.
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