I presume that by ‘memory’ you mean storage. Memory is sometimes called RAM (Apple doesn’t use that term anymore because the memory is now ‘universal’ meaning shared across CPU and GPU).
You should aim to have 15-20% of your total internal storage as free space (~30-40 GB as an absolute minimum). If you do not have enough free space on your Mac’s internal storage, then here are some steps to take to safely free up space:
Free up storage space on Mac - Apple Support
Optimize storage space on your Mac - Apple Support
How to free up ‘System Data’ and other st… - Apple Community
"System Data" comprises your data, but they are typically hidden files that Spotlight cannot assign to a specific category like Documents or Applications. Examples include Outlook attachments, iOS updates, Cloud storage caches, etc. Starting with macOS 27 Golden Gate, System Data also includes what macOS used to call ‘purgeable’ storage – system caches, Time Machine snapshots and some other data, though the user had no control over the purging. Trying to manually clean out hidden files in System Data is likely to cause more problems than it solves, macOS hides those files for a good reason. Follow the steps in the linked articles above.
On macOS 27, separate ‘purgeable’ space is no longer reported, and instead those data are now considered as used space. They are also now included in System Data, accounting for the apparent increase you (and others) have noticed. You didn't lose space, macOS just categorizes things differently now than on Tahoe.
More detail on this change in this User Tip:
System Data and Free Space Changes in Gol… - Apple Community
The best advice is to just ignore the System Data category. ‘System Data’ is merely a catch-all category for files that Spotlight cannot assign to specific categories like Applications, Documents, Photos, etc. In fact, what is now shown as System Data used to be reported as ‘Other’, Apple changed the label in macOS 12 Monterey. System Data probably sounds better, but Other was closer to reality.
REgarding your comment about Apple Intelligence, the user tip that you link has a somewhat misleading title, Apple phrases it more accurately in their support article:
Turn off and restrict access to Apple Intelligence features on Mac
As Apple states, you can turn off and/or restrict access to some features of Apple Intelligence, but you cannot turn off Apple Intelligence altogether.
Apple Intelligence features can be restricted in a more comprehensive way by using a declarative configuration, but that requires device enrollment (i.e., management of the Mac with MDM) and that is beyond the typical processes with which most users are familiar. However, there is a script called Remove Mac AI that is available to execute those functions as a local Profile via a terminal command, if you are comfortable using it. At least one long-time member here has done so without issue. Use it at your own risk, but that process will remove the space used by Apple Intelligence, ~33 GB on my Mac.
User level: Level 1 (10 points)
