What is Epoch Time and How to convert this in human understandable format?

What is Epoch Time and How to convert this in human understandable format?

An epoch means an instant in time chosen as the origin of a particular era .The "epoch" then serves as a reference point from which time is measured. Time measurement units are counted from the epoch so that the date and time of events can be specified unambiguously.

Events taking place before the epoch can be dated by counting negatively from the epoch, though in pragmatic periodization practice, epochs are defined for the past, and another epoch is used to start the next era, therefore serving as the ending of the older preceding era. The whole purpose and criteria of such definitions is to clarify and co-ordinate scholarship about a period, at times, across disciplines.
Epochs are generally chosen to be convenient or significant by a consensus of the time scale's initial users, or by authoritarian fiat. The epoch moment or date is usually defined by a specific clear event, condition, or criteria— the epoch event or epoch criteria —from which the period or era or age is usually characterized or described.

In case of SEPM , the time is stored in the database is the time when this database record was entered or modified in the database, in milliseconds since 1970.

Now , the question is how should we convert this integer into human understandable form.

There are 2 ways  in which we can do this:

    1. Go to http://www.epochconverter.com/ and use the Epoch Converter. This converter will change the time stamp to human date. It can also do vice versa

    2. We can query it from the database using either of the two 

     Creation_Time/1000, '1/1/1970 00:00')[Creation Time]

    Or

    time_stamp /86400000 + DATEADD (ms,time_stamp%86400000,'19700101') as 'Time Stamp'

Example:

SELECT computer_domain_name,computer_name,current_login_user,ip_addr1_text,dateadd(s, Last_scan_time/1000, '1/1/1970 00:00')[Last Scan Time]
 
FROM sem_agent
INNER JOIN v_sem_computer ON sem_agent.computer_id=v_sem_computer.computer_id
WHERE last_scan_time > '0'

OR

SELECT Computer_Name [Computer Name], dateadd(s, Creation_Time/1000, '1/1/1970 00:00')[Creation Time] from SEM_CLIENT