Vault 13 holodisk is a holodisk in Fallout 2. Described as containing the location of Vault 13, when used, it marks the location of Fake Vault 13.
Location
Can be bought from Merk in the New California Republic for $1000.
Transcript
VAULT 13 HOLO by Ziggy
This holodisk gives the location of Vault13. The location has been marked on your map.