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iOS and macOS™ Performance Tuning: Cocoa®, Cocoa Touch®, Objective-C®, and Swift™ by Marcel Weiher

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10. I/O: Principles

When Apple introduced the PowerMac G4, it was billed it as the world’s first desktop supercomputer. Ken Bachter once quipped that “a supercomputer is a device for turning compute-bound problems into I/O-bound problems.” In a sense, all

computers are supercomputers now, with today’s iPhones vastly outpacing a PowerMac G4, and with compute performance vastly outpacing I/O performance. In addition, the difference between access times (latency) and transfer speeds (bandwidth) that we saw with memory access is even more pronounced with I/O devices. Whereas the difference between latency and throughput is around 1:100 with memory, it is 1:100,000 and more with I/O devices.

Hardware

The fundamental performance characteristics of ...

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