As the fourth generation Apple's MP3 player, iPod 40GB sports a click-wheel navigation; 12-hour battery life; and dual FireWire 400 and Hi-Speed USB interface support plus battery re-charging. But missing are a remote and belt clip. It doesn't matter anyway since Apple discontinued this model in favor of the 30GB photo and 60GB photo, both of which have 65k color LCD.

Specifications

Dimensions
4.1" x 2.4" x 0.69"
 
Weight
6.2 oz.
 
Natively supported music format(s)
MP3, AAC, WAV, Audible, AIFF, Apple Lossless

Battery life
12 hrs. 
 
Storage
40GB built-in hard drive

FM tuner
Optional via 3rd party add-on
 
Voice recording
Optional via 3rd party add-on

Software iTunes
4.6 for Mac, Windows

Inputs / outputs
Headphone jack

Power source
Built-in Li-Polymer battery rechargeable via USB port
 
Warranty
One year (optional AppleCare 2-year service)

Review

The player against which all others are judged, despite limited features compared with those of newcomers and a high price.

Pros:
Slim, attractive player. Excellent ergonomics. Wired remote. Solid audio performance.
Cons:
No FM or recording. Expensive

Source:
http://www.pcmag.com