Eugene's observations

When you add a USB thumb/pen/flash drive to your PC you will see an icon in the system tray enabling you to 'Safely Remove Hardware' with a mouse click. This is always good to do before pulling the device out as it causes unwritten data to be flushed out of volatile memory. But sometimes the system disk C: is listed there - how come ?

This is noticeable with disks that connect using Serial ATA sockets. Apart from an increase in speed over the earlier drives, the SATA specification allows for hot swappable or hot pluggable devices. Where these are accessible from outside the computer case they are known as External SATA devices (eSATA). Being able to easily (dis)connect a disk from your running PC is obviously handy for backups and RAID configurations, but apart from just having an eSATA connection, to be able to safely remove disks with the system running two attributes need be active.

First, you'll need a SATA controller that supports hotpluggability, an second, you'll need to enable AHCI mode - which itself has to be done before installing Windows. AHCI is supported natively by Windows Vista, but older operating systems require drivers written by the host bus adapter vendor in order to support AHCI.

You'll know when it is all working because the SATA drive will be presented in the system tray as stoppable, even when it is the disk the system booted off and is therefore not stoppable. Hotplugging hard disks in an unsupported system could result in lost or corrupted data or possibly even fried hardware.