The top four numbers represent sequential speeds, both in read and write.
The bottom four numbers represent random speeds, both in read and write.
To first address read/write.
Read: reading a file, which would include opening a file, opening a program, starting your OS, etc.
Writing: when you are creating/editing a file and making new data to be saved.
Sequential vs. random.
Sequential is generally the simpler of the two, it's reading or writing data in a sequential pattern, one after the other.
Random read/write is when data may be found on different parts of the disk, so the controller needs to be able to find these different parts to read/write efficiently and fast.
The memory on the drive may be fast in sequential reads/writes, but if the controller can't keep up with the random requests, it may still prove slow in day-to-day use.
HDD's for example have 'okay' sequential performance, but really poor random performance, which generally makes them crappy as an OS/program drive.
The reason I say this, is because 'real life' work is often just not laid out in a sequential way, requiring the controller to find data/space all over the drive.
CrystalDiskMark also has small and large file tests, because a controller may perform differently with many small requests, compared to fewer large requests.
"SEQ1M", "SEQ128K". The '1M' and '128K' stand for 1MB and 128KB respectively, showing the sort of size files these tests use (although I don't know for sure if those are actually the sizes, I always just figured that was the case.
Read speeds, generally sequential, because the program is saved in one place.
Write speeds, because you're saving a file. Generally sequential and large sizes, unless the controller has to 'find' free space some place else.
These are both pretty intensive applications, for both reading and writing. Often sequential and random.
Mostly these would be sequentially read applications.
Reason I say this, is because when - for example - working on a video, it needs to load videos from some place else on the disk, in varying sizes and bitrates. These video clips may be saved in a different sort of format in the video editing program, to speed up the editing process, etc.
EDIT: I've been thinking a bit more on this. I think video editing especially so, is a mix of random and sequential read/write. A bit of everything really. I can't say it's more one thing vs. another.
If you want to figure out (or estimate really, it's not an exact science) if read/write and seq/random is important for the work, try thinking about what the program does.
Many small files, or few large ones? That would make you figure out if you should look at 1M or 128K for example.
Does it save data, or retrieve data? That would be write and read respectively
Is all the data in one place (generally), or not? sequential and random respectively.
But keep in mind, this is not an exact science, as it's pretty much impossible to figure out what is the most important for all programs. Plus, programs change over time too.
Puget Systems has some great tests, but from what I can see, they mostly have tests that compare different storage solutions (HDD vs. SATA SSD vs. PCIe/NVME SSD) and not in-depth in specific SSD's.
