A state where the OS waits until the device is ready to receive a command by repeatedly reading the status register is called

The state where the Operating System (OS) waits until the device is ready to receive a command by repeatedly reading the status register is called "Polling".

Here's a step-by-step explanation:

1. The OS sends a command to the device.
2. The device takes some time to process the command and become ready to receive the next command.
3. During this time, the OS repeatedly reads the status register of the device. The status register is a special type of register that provides information about the status of the device, such as whether it's busy, ready, etc.
4. This state of repeatedly checking the status register to see if the device is ready is called "Polling".
5. Once the status register indicates that the device is ready, the OS can send the next command.

So, in essence, Polling is a method used by the OS to check whether a device is ready to receive a command or not.