The thin, lightweight Thinkpad X21 notebook from IBM has been designed for users who want a fully functional laptop that is easy to carry. While the X21 on its own doesn't fulfil that need, by adding the optional lightweight media slice it becomes a very useful ultra-portable. Despite being thin, and only weighing 1kg, this notebook's good build quality is apparent and apart from the screen, which is a little flexible, the X21's solid construction puts many larger notebooks to shame.

Powered by a 700MHz Mobile Pentium III processor and 128MB of SDRAM memory, the X21 performs well enough and its 20GB hard drive provides plenty of storage space. To keep the weight and dimensions to a minimum, several features have been omitted from the notebook itself and are built into the media slice. For example, there are no serial or parallel ports built in, nor any way of using a PS/2 mouse or keyboard.

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On the plus side you do get a single PC Card slot, a CompactFlash Type II slot (ideal for IBM's range of Microdrives), two audio ports (mic and headphones) and a VGA socket for an external monitor, but there's no infra-red port. For connectivity the Thinkpad X21 we reviewed came with a combined 3Com mini-PCI card containing a 56Kbps modem and a 10/100Mbps network adapter.

As mentioned above, most of the drives are built into the optional media slice. The UltraBase X2 adds another 1kg to the overall weight, but has an integrated Ultrabay 2000 media bay, which allows for the swapping of optional media and storage devices. The one supplied with our review machine came with a 6-speed DVD-ROM drive installed. The UltraBase X2 also provides a floppy drive, serial and parallel ports, a PS/2 port and two speakers.

The notebook's 12.1-inch TFT screen is powered by a 4MB ATI Rage Mobility M graphics chip, which allows for a maximum native resolution of 1,024 pixels by 768 pixels. The keyboard is well built and laid out, and feels secure when in use, while above the keyboard are the volume buttons and the ThinkPad button, which opens the useful online help and information centre.

One aspect of the Thinkpad X21 that is particularly impressive is the life of its 3,600mAh Li-Ion battery; under test it gave an excellent three and a half hours of use.

The ThinkPad X21, although expensive, is a well-built and surprisingly solid machine. It's easy to use and has excellent battery life and good connectivity, which many systems in this market segment fail to achieve.