DHCP clients store information locally so that they can attempt to lease the same IP address and still function if the DHCP server is down.
A Windows NT client stores DHCP information in the registry at:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\<Network Adapter>\Parameters\Tcpip
A Windows 95 client also stores DHCP information in the registry at:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\VxD\DHCP\DHCPInfo00
Windows for Workgroups with TCP/IP-32 stores the DHCP-related information in the DHCP.bin file in the <WINDOWS_SYSTEM_ROOT> subdirectory. This file is in binary format.
LAN Manager version 3.0 and LAN Manager for MS-DOS version 2.2c clients both store the local DHCP-related information in the DHCP.prm file in the <NETWORK_ROOT> directory. This file is in a binary format.