What is uptime, downtime and how to calculate it?

It is important to understand some basic terms when we speak about uptime. Uptime can be defined in several ways, which can be divided into two smaller groups.

• Uptime as an amount of time since system has been turned on:

Uptime is a measure of the time a device has been running.

• Uptime as a calculated number that shows amount of time since system has been turned on during a given time period:

Uptime is a calculation of the amount of time a device is online, available, and functioning during a given time period.

Similarly, we can define also downtime.

• Downtime as an amount of time since system has been turned off:

Downtime is a measure of the time a device has not been running.

• Downtime as a calculated number that shows amount of time since system has been turned off during a given time period:

Downtime is a calculation of the amount of time a device is off-line, unavailable, and not functioning during a given time period.

Let us consider uptime that shows only the time a device has been running. We could see for example uptime value: 1 day 2:20:10. This would tell us that the system started running 1 day 2 hours 20 minutes and 10 seconds ago. We could tell also the exact time when the system started, but nothing more. Sometimes this is enough, but sometimes it is not.

We need to know the uptime as a relation between uptime and downtime when it describes some crucial process, which must be always available. Usually this relation is used in Web Hosting, where companies list their server uptime in percentage, for example, "99.9% uptime." Uptime in Web Hosting is very important measure that shows you how well the Hosting provider is doing its job – to keep servers running, and your web site being served to its visitors.

I will list also some statistics now. If somebody says 99.9% uptime, what does that mean? Here's a list that shows how much downtime one may experience over the course of one year (366 days):

You can download a handy MS Excel Uptime calculation worksheet that allows converting uptime expressed in percentage to uptime expressed in days and time for any time period of your preference.

First post!

Hi there folks!

This is the first post and I am looking forward to sharing my view on the various topics on uptime, availability and downtime.

This blog has been created with the intention to help people find information they need and organize it in an understandable way.

Main focus will be on topics and details which are related to uptime on Windows OS.