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2020 iMac 5K: SSD Speed vs Transfer Size
Related: 2019 iMac 5K, 2020 iMac 5K, 4K and 5K display, computer display, iMac, iMac 5K, Macs, memory, SSD, video
MPG tested the 2020 iMac 5K 3.6 GHz Intel Core i9 10-core / 128GB / 2TB / Radeon 5700. Smart move: buy with 8GB memory, then add 64GB or 128GB OWC memory to save a ton on memory cost (same memory as 2019 iMac 5K).
This test charts the real-world speed for various transfer sizes for both reads and writes, because small I/O sizes are much slower than larger ones.
For example, 32K transfers are highly inefficient vs 1MB transfers—there is a difference of 32X times as many operating system calls to transfer 1MB in 32K chunks as with one call to transfer a 1MB chunk.
Fast small transfers translate to a more responsive system overall, while fast large transfers translate to better throughput for applications processing very large files, or very large numbers of moderate and large files.
Sustained transfer speed vs transfer size
The 2020 iMac 5K SSD disappoints for small reads—it’s a dog compared to the 2019 iMac 5K. However, its write speed is much superior.
Speed of the 2019 iMac 5K (red/green lines) are not as originally tested for large transfers (test was run twice, with identical results). After nearly 3 years of use, perhaps its SSD has slowed down after all the usage from internal fragmentation and wear-leveling?