In SSH, a key pair, called as host keys is used to identify a computer. The purpose of SSH key pair is for authenticating computers. Host keys are unique and generated using asymmetric encryption algorithms like RSA, DSA, or ECDSA algorithms. Public host keys distributed to SSH clients, and private keys are stored on SSH servers.
When an SSH client connects to an SSH server, the host key of the SSH server is stored in a file, called as known host keys.
In Unix/Linux OpenSSH, the collection of known host keys is stored in /etc/ssh/known_hosts and in .ssh/known_hosts in each user's home directory. PuTTY for Windows stores the known host keys in Windows registry HKEY_CURRENT_USER\SoftWare\SimonTatham\PuTTY\SshHostKeys.
OpenSSH client for Windows stores the known hosts file within %USERPROFILE%\.ssh folder. To open %USERPROFILE% folder, type "explorer %USERPROFILE%" in your command prompt, PowerShell or Run box, and hit Enter key (without double quotes).