This acronym has three meanings depending on the context:
TTL (Transistor-Transistor Logic) : a
robust family of IC chips often used by home experiments. You can build primitive computers with and and or
TTL (Time To Live) : The number of hops a
packet can take on the Internet before it is euthanised. Without this, errors in the Internet’s routing
tables might send a packet hopping from place to place forever, like Charlie in the subway. On evey hop, this
count in the packet header is decremented. A packet may typically take 7 to 30 hops to get to its destination.
You can use tracert mindprod.com to see the hops the packets from you to my website
get here. Each hop typically takes about 30 milliseconds.
TTL : How long a DNS (Domain Name Service) cache
entry should be kept before it is considered stale. DNS is the lookup of a human name like mindprod.com to its computer numeric ip
, much like an
automated phone book would look up human names to get their phone numbers. DNS caches refresh themselves as
needed from an upstream name server, cascading all the way back to the authorative source, a computer owned by
the owner of the domain or his ISP (Internet Service Provider). Typically entries are cached for a day. Dynamically assigned names might
have a TTL as low as 30 seconds.