Count seconds from the 1900 epoch
01A time value counts seconds from a fixed origin, called an epoch. It is a binary number, not a formatted date string.
2,208,988,800 seconds corresponds to midnight, 1 January 1970 GMT. The number labels a 32-bit binary value, not a text message.
Source for this drawing: RFC 868 · Read RFC source: The Time · page 2 ↗
New to this? Start hereA quick picture + helpful background
Two clocks may disagree.
A device compares timestamps with another clock. Network delay makes that comparison imperfect. The drawing separates the clock reading from the trip the message takes.
Helpful first, if these ideas are unfamiliar
These pictures are analogies to help you learn. The linked RFC explains the actual rules.
Terms in this drawing
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
A number needs an agreed origin and unit.
- The epoch is 00:00 on 1 January 1900 GMT; the value 1 means one second after it.
- The reply carries an unsigned 32-bit binary number (verified erratum 2528). Decimal labels here explain values; they are not ASCII reply bytes.
- RFC 868 lists 2,208,988,800 for 00:00 on 1 January 1970 GMT.
This chapter illustrates positive values from the RFC, not a complete wire decoder. Verified editorial erratum 2528 clarifies that the value is unsigned and the negative pre-1900 example is illegal for this protocol. The RFC does not explicitly specify byte order; do not infer it from the left-to-right drawing. See https://www.rfc-editor.org/errata/eid2528.
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