Linux buffers and cache what's the difference?

If I do 'sar -r 1 1' I get output like:

[root@sukdbs03 ~]# sar -r 1 1
Linux 2.6.18-194.3.1.el5 (sukdbs03.offices.global)      07/20/2010

03:06:18 PM kbmemfree kbmemused  %memused kbbuffers  kbcached kbswpfree kbswpused  %swpused  kbswpcad
03:06:19 PM    128524   8046648     98.43    381348   6722556   8041044     47672      0.59      4656
Average:       128524   8046648     98.43    381348   6722556   8041044     47672      0.59      4656

The man page for sar shows the following definitions:

              kbbuffers
                     Amount of memory used as buffers by the kernel in kilobytes.

              kbcached
                     Amount of memory used to cache data by the kernel in kilobytes.

The free command also distinguishes between buffers and cached. Please could someone explain the difference?

Thanks, Steve