About the things specifications for Inspiron531s don't tell us.

Specifications for this machine tell us its memory is 512MB or 1GB. This machine I selected indeed has two 512MB memories. Picture A shows two preinstalled 512MB memories work normally. The software package for this verification is Memtest86 (http://www.memtest86.com, Download-Memtest86 v3.4a ISO image(zip)).

Picture A

At the same time, there are well-known things in the things specifications for this machine don't tell us. Its memory capacity is above 1GB and can be 2GB. Picture B shows two 2GB memories work
normally.

Picture B

Memories used in this verification are DDR2 PC2-6400 2GB x2 (Pulsar DCDDR2-4GB-800).