How does cmms work is best answered as a loop rather than a feature list. Computerized maintenance starts with a register of assets, puts a schedule against each, raises work orders from the schedule and from breakdowns, records what was done, and feeds that history back into the schedule. Computerized maintenance management systems cmms vendors describe the same loop in different words. This page walks it once round, says what maintenance cmms systems do at each step, and starts with a maintenance management system definition, because the software only makes sense against the function it serves.
A maintenance management system definition
Maintenance management is deciding what the equipment needs, getting it done, and knowing afterwards what was done and what it cost. A maintenance management system is whatever holds those decisions and records: a clipboard and a diary, a spreadsheet, or software. The computerised version is a CMMS, and the definition matters because every screen in the software corresponds to one of those three activities; a feature that does not is decoration.
Step one and two: the register and the schedule
The register is the list of assets, arranged as a tree so that a work order can be raised against a component and reported against a line. The schedule is the preventive tasks against each asset and the interval each runs on, by calendar for a monthly inspection or by meter for a service every so many hours. The schedule is where the maintenance strategy lives: change the interval and you have changed the strategy for that asset.
Step three and four: work orders and history
When an interval comes round the system raises a work order, and when something breaks a person raises one. Each has an asset, a priority, an assignee and a status. The technician does the job and records what was found, what was replaced and how long it took, then closes it. That closed work order is history: it is what MTBF, MTTR and cost by asset are calculated from, and it is what the next technician reads before opening the machine.
Back to the schedule
The loop closes when the history changes the schedule. An asset whose reactive work orders keep arriving between preventive tasks gets a shorter interval or a different task. One whose preventive tasks find nothing for a year gets a longer one. A team that never adjusts the schedule from the history is running the software without the loop, and the worked example on this site, 240 work orders a month with 35% of them reactive, is the picture of a schedule that has not yet been adjusted.
Questions people ask about how does cmms work
Does a CMMS need the internet?
Cloud systems do for the office; the mobile app usually works offline on the floor and syncs later. A plant with no signal in the basement should test that before buying.
How does the schedule know the meter reading?
Somebody enters it, or a meter feeds it. Most small teams enter readings on the work order that visits the asset, which is enough for a service interval in hours.
What happens to work orders that are not closed?
They stay open and become the overdue list. A CMMS does not close them for you, and an overdue list nobody reads is the first sign the loop has broken.
Can the loop run without software?
Yes, for a small register. The maintenance log worksheet on this site is the loop on paper, and it is the right place to start if the team has never kept history.