1. S1 (Standby or Sleep): This mode is also known as Sleep mode or Standby mode, and it is the most basic sleep state. The system enters a low-power state, but it can quickly return to normal operation when the user wakes it up by pressing a key or moving the mouse.

2. S2 (Standby or Sleep): This mode is similar to S1, but it has a deeper sleep state. The system enters a low-power state, but it takes a bit longer to resume normal operation when the user wakes it up. This mode is used to conserve more power than S1.

3. S3 (Suspend to RAM): This mode is also known as Suspend-to-RAM (STR) or Standby mode. The computer enters a low-power state, but it retains the contents of the RAM. This allows the computer to quickly resume normal operation when the user wakes it up.

4. S4 (Hibernation): This mode is also known as Suspend-to-disk (STD) or Hibernation mode. The computer enters a low-power state and saves the contents of the RAM to the hard disk. This allows the computer to resume normal operation when the user wakes it up, even if the battery is dead or if there is a power failure.

Some laptops may not support all types of sleep modes to check which kind of sleep mode is supported in your laptop open the command prompt and type,

"powercfg /availablesleepstates".

Here is an example,

on this laptop, only s3 sleep is supported, and rest modes are unavailable.