IE7 (2006) introduced Protected Mode, which runs browser tabs in separate, sandboxed processes to isolate tabs from each other and from the OS, communicating with central Broker processes that remain privileged and provide system services. Chrome’s architecture was designed similarly.
IE7’s Protected Mode uses Vista’s Mandatory Integrity Control, which prevents processes from modifying any files, allowing them to write only to locations marked as low, such as Temporary Internet Files. Files touched by processes are marked with their integrity level. Integrity Levels correspond to Internet Zones. Chrome on Vista also leverages MIC.
IE8 introduced InPrivate, among a bevy of other features. InPrivate is similar to Incognito browsing in Chrome.