In-place versus side-by-side upgrade

Detaching a database is simply closing the database, flushing the transaction log, and removing entries in sysdatabases. Attaching a database is simply placing entries in sysdatabases and opening the database files. It doesn't matter whether the database is 1 MB in size or 1 TB in size. It will depend on the volume of transactions required to be flushed to disk. When you detach a 7.0 database and attach it to SQL Server 2000, it undergoes an additional process of converting the metadata and making necessary changes to system tables, and I have no time estimates on that. Upgrading in place simply means dropping all of the new binaries and updating metadata and system objects. I don't do upgrades via detach/attach. If I'm going to upgrade it, I backup all databases, ensure I have orginal SQL Server 7.0 installation media along with any service packs which were applied in the event I need to roll back to previous version and then just upgrade it in place.