In the days of Classic Macs, most of our concerns centred on memory rather than CPU, disk or network performance. Tools for managing memory flourished, and I don’t recall any utility provided in Mac OS that looked more broadly. That changed when Mac OS X arrived, and we started taking an interest in Process Viewer and CPU Monitor.

CPU Monitor, seen here in 2001 with its two floating chart views, was a first step in development. I suspect this was taken on my QuickSilver Power Mac G4 with its dual processors, hence the pair of CPU charts.

Process Viewer is a more obvious ancestor of the modern Activity Monitor, with its list of processes in a column view. Note the surprisingly few system processes running at the time: only 34, compared with today’s list of several hundred.

Activity Monitor integrated those features into its new app in Mac OS X 10.3 Panther in 2003, and is shown here in 10.4 Tiger from a couple of years later, where it’s surprisingly similar to the current app. There are still only 72 processes running, though, and most have less than 5 threads.

Here’s Activity Monitor with its CPU History window on an 8-core Mac Pro, running Mac OS X 10.7 Lion in 2011. The number of processes is still only growing slowly, and had reached 89.

Xcode’s Instruments added an Activity Monitor template for developers wanting to monitor further details as they tested and debugged their code. At this stage it was limited to presenting the same fundamental measurements as were available in Activity Monitor, but these have since flourished into much greater depth.

Two years later, in 2013 for OS X 10.9 Mavericks, Activity Monitor underwent revision to add a new tab for Energy. Unlike other panes, the ‘Energy Impact’ is given in arbitrary units rather than calculating Joules from power use over time. It was at about this time that the app also added a Cache pane analysing the performance of the Content Caching service, when enabled on the Mac.

Until 2020, Activity Monitor had dealt with CPUs with uniform cores. Above are the eight physical and eight Hyper-threaded cores in an 8-core Intel Xeon W in an iMac Pro from 2017, running a heavy load of over 700% CPU. With the first Apple silicon Macs, it had to display CPU use for two different types of core. Note how, by 2020, the total number of processes has shot up to 458.

This is an example from one of the first base M1 Macs, with 4 Efficiency and 4 Performance cores displayed neatly in its CPU History window. Although Activity Monitor doesn’t take core frequency into account when measuring % CPU, and can’t display cluster frequencies, it remains one of the essential tools for everyone, whichever age and architecture their Mac.