I have two x 2GB DDR3 sticks in my machine, as confirmed by lshw below.
Why does sysinfo and meminfo show 3GB?
This is x86_64. 10.04 LTS

sysinfo shows:
3018MiB

=============
cat /proc/meminfo | grep MemTotal
MemTotal: 3090800 kB


======
lshw
*-memory
description: System Memory
physical id: 2d
slot: System board or motherboard
size: 4GiB
*-bank:0
description: DIMM Synchronous 1333 MHz (0.8 ns)
product: PartNum0
vendor: Manufacturer0
physical id: 0
serial: SerNum0
slot: DIMM0
size: 2GiB
width: 64 bits
clock: 1333MHz (0.8ns)
*-bank:1
description: DIMM Synchronous 1333 MHz (0.8 ns)
product: PartNum1
vendor: Manufacturer1
physical id: 1
serial: SerNum1
slot: DIMM1
size: 2GiB
width: 64 bits
clock: 1333MHz (0.8ns)