Lenovo T23 uses 15, 30, or 48GB hard disks. It depends on its configuration. It is IDE or, in other words, ATA interface and it looks like this:

It can be replaced with hard drives with ATA interface, produced by various companies, such as Toshiba, IBM, Hitachi, WD, etc.

It is located on the left side of the laptop near it’s corner:

 

To replace T23 hard drive we need to unscrew a screw, which is located underneath the laptop, as it is shown in the picture below:

It is the biggest screw of the laptop. When you notice it, you just have to slide the hard drive compartment, as shown in the picture below:

The hard drive compartment is screwed with 4 screws to the casing, so they have to be unscrewed. You should remember the way the casing is attached to the plastic cover. Then you will be able to attach it easily, if you would assemble it again.