Editing high resolution footage on a modest machine is completely feasible and a lot of people conclude it is not, because they tried it directly, found it unusable, and assumed they needed a new computer.
The technique is proxies, which nearly every editing application supports and which is routinely configured badly.
What a proxy actually is
A low resolution, lightly compressed copy of your footage that the editor uses for playback instead of the original.
You edit the proxy. All your cuts, timings and decisions apply to the timeline rather than to the file. When you export, the software switches back to the original media and renders from that.
The result is a full quality export produced from an edit that played smoothly on hardware that could not play the original at all.
Why high resolution footage is hard to play
Worth understanding, because it explains why proxies work so well.
Most camera codecs use inter-frame compression, meaning most frames are stored as differences from other frames rather than as complete images. Playing them requires reconstructing each frame from several others, which is computationally expensive.
This is fine for playing forward at normal speed. It is terrible for editing, where you scrub backwards, jump around, and play at odd speeds, because every jump requires reconstruction from the nearest complete frame.
Proxy codecs are intra-frame, meaning every frame is stored complete. Files are larger and decoding is trivial, and scrubbing becomes instant.
So the gain is not only from lower resolution. It is largely from a codec designed for editing rather than for recording.
Getting the settings right
The mistakes here are consistent.
Resolution: quarter of the original in each dimension is generally right. From four thousand pixels wide, that is around a thousand, which is plenty to judge focus and framing on a laptop screen.
People set proxies at half resolution to keep quality, and then wonder why playback is still poor. You are not going to grade on the proxy. Make it small.
Codec: whatever intra-frame editing codec your software prefers. The important thing is that it is intra-frame, not which one.
Audio: leave it uncompressed or lightly compressed. Audio is a tiny fraction of the data and compressing it gains nothing while risking sync issues.
Where to put them
The single most impactful decision and the one people get wrong.
Proxies should be on the fastest storage you have, which is almost always the internal drive, and the original media can live on a slow external drive.
This is counterintuitive because the originals feel more important. But during editing you touch the proxies constantly and the originals not at all. The originals only matter at export.
Editing with proxies on a slow external drive over a slow connection removes most of the benefit, and this is the configuration a lot of people end up with by default.
Generating them without waiting
Proxy generation takes time proportional to the footage. For a large project this can be hours.
The practical approach is to start generation and go and do something else. Most software will run it in the background and let you work, badly, while it goes.
Better, if your camera supports it, is to record proxies in camera. Many cameras will write a low resolution copy alongside the main file, which eliminates the generation step entirely. This is one of the more genuinely useful camera features and it gets very little attention.
And if you only need part of the footage, generate proxies only for the selects rather than for everything. Reviewing footage to make selects can be done at whatever playback quality is bearable.
The things that go wrong
Forgetting to switch back before export. Most software handles this automatically now and older versions did not, and there are a lot of accidentally low-resolution exports in the world because of it. Check the export resolution before delivering.
Moving or renaming original media after generating proxies, which breaks the link. Sort out your file structure before you start.
Judging focus on a proxy. A quarter resolution copy will not show you whether a shot is critically sharp. Toggle back to the original for that check, on the shots where it matters.
Same for grading. Never grade on proxies. The compression will hide banding and noise that are present in the original.
What else helps on slow hardware
Beyond proxies, a few things make a real difference.
Reduce the playback resolution in the preview window. This is separate from proxies and stacks with them.
Turn off any effects during playback. Most software has a global toggle and a single unrendered effect can halve playback performance.
Work in shorter sequences and nest them, rather than one enormous timeline.
Close everything else. Editing software wants all the memory it can get and a browser with thirty tabs is competing for it.
The honest limit
Proxies solve playback. They do not solve export, and a long project will still take a long time to render on a slow machine.
They also do not solve heavy effects work, colour grading with many nodes, or anything that has to process the original footage in real time.
For ordinary cutting, which is most of editing, they eliminate the hardware problem almost entirely, and a five year old laptop with proxies set up properly is a perfectly reasonable editing machine.