Take a look at his descriptions from the command reference:
http://www.cisco.com/en/US/products/sw/secursw/ps2120/products_command_reference_chapter09186a00801727ae.html#wp1027782
write erase = Clear the Flash memory configuration.
The following example erases the contents of Flash memory and reloads the PIX Firewall:
example:
write erase
Erase PIX configuration in Flash memory? [confirm] y
reload
Proceed with reload? [confirm] y
-------------------------
clear configure
Resets command parameters in the configuration to their default values.
http://www.cisco.com/en/US/products/sw/secursw/ps2120/products_command_reference_chapter09186a00801727a6.html#wp1055799
configure
Configure from the terminal, Flash memory, the network, or factory default. The new configuration merges with the active configuration except for the factory default, in which case the active configuration is cleared first and then replaced by the factory default. The factory default option is available only on the PIX 501 and PIX 506/506E.
clear configure [terminal | memory]
clear configure [primary | secondary | all]
[no] configure http[s] :// [user:password@] location [ :port ] / http_pathname
configure net [[location]:[filename]]
clear configure primary | secondary | all
show configure
For the PIX 501 and PIX 506/506E only:
configure factory-default [inside_ip_address [address_mask]]
sincerely
Patrick
