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2017 iMac 5K: XCode Build C++ Project
MPG recommends 64GB OWC memory (big savings!) in: 27" Retina 5K Display, 4.2 GHz Intel Core i7 (Skylake), 1TB Flash, 8GB memory, AMD Radeon Pro 580 Graphics Card (8GB).
The machines tested here are the fastest possible CPUs as of mid 2017.
XCode build diglloydTools (C++)
Builds were run repeatedly (and after rebooting) to check the results, with the iMac 5K winning every time by a small but clear-cut margin.
This test uses all CPU cores, which implies an easy victory for the 2013 Mac Pro with its 8 CPU cores, versus the 4 CPU cores of the iMac 5K. But it is not so: the 4-core 2017 iMac 5K 4.2 GHz sails to a clear-cut victory over the 8-core Mac Pro.
There are two likely explanations, both of which apply:
- The flash drive / SSD in the late 2015 iMac 5K is considerably faster ; this was also seen in the Integrity Checker Verify test. The XCode build must write its binary compilation products as well as the application binaries (source files are small and entirely cached after the first build). The faster these writes occur, the more the CPUs can be used. Relatively idle periods of CPU usage were observed at key points in the build (using Activity Monitor).
- The 4 CPU cores in the iMac 5K run at 4.2 GHz (min). That’s 27% faster than the 3.3 GHz of the 2013 Mac Pro. This clock speed difference makes the iMac 5K roughly equivalent to a 5-core 3.3 GHz CPU in throughput terms. Together with the slower I/O, the CPUs of the 8-core Mac Pro just do not get utilized more than about half the time.
Bottom line: fast CPUs require ultra-fast SSDs for disk I/O or CPU usage will suffer. The late 2015 iMac 5K delivers the goods. The 2013 Mac Pro is badly in need of an SSD upgrade that delivers iMac 5K performance. Perhaps Apple waits to implement the new Thunderbolt 3 standard: Thunderbolt 3 includes support for NVM Express, which will allow external SSDs capable of 2.4 GB/sec speeds.