A maximum transmission unit (MTU) is the largestsize packet or frame, specified in octets (eight-bit bytes), thatcan be sent in a packet or frame-based network such as theInternet. The Internet´s Transmission Control Protocol usesthe MTU to determine the maximum size of each packet in anytransmission. Too large an MTU size may mean retransmissions if thepacket encounters a router that can´t handle that large apacket. Too small an MTU size means relatively more header overheadand more acknowledgements that have to be sent and handled. Mostcomputer operating systems provide a default MTU value that issuitable for most users. In general, Internet users should followthe advice of their Internet service provider (ISP) about whetherto change the default value and what to change it to.

In Windows 95, the default MTU was 1500 octets (eight-bitbytes), partly because this is the Ethernet standard MTU. TheInternet de facto standard MTU is 576, but ISPs often suggest using1500. If you frequently access Web sites that encounter routerswith an MTU size of 576, you may want to change to that size.(Apparently some users find that changing the setting to 576improves performance and others do not find any improvement.) Theminimum value that an MTU can be set to is 68.

For more recent Windows systems, the operating system is able tosense whether your connection should use 1500 or 576 and select theappropriate MTU for the connection.