It's certainly not IO-bound. Think about the Linux kernel. It's compiling on the order of 100MB of source code into something of the same order of magnitude of binary objects, and it takes minutes. That is a not close to saturating any kind of disk device. Not to mention that the intermediate files will be cached in RAM by the file cache and can be used without them hitting the disk.
My kernel directory is 13GB, most of that is intermediate build products. Linus has written somewhere on how much faster kernel compilation is with an SSD.
My dual-SSD striped setup with humongous throughput (600MB/s) made a kernel compilation 1.4% faster compared to using a 5400rpm HD. But then I have 16GB RAM, and RAM is a huge bottleneck in its own right, as swapping or pushing out the file cache will kill compilation times.
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It's certainly not IO-bound. Think about the Linux kernel. It's compiling on the order of 100MB of source code into something of the same order of magnitude of binary objects, and it takes minutes. That is a not close to saturating any kind of disk device. Not to mention that the intermediate files will be cached in RAM by the file cache and can be used without them hitting the disk.
My kernel directory is 13GB, most of that is intermediate build products. Linus has written somewhere on how much faster kernel compilation is with an SSD.
My dual-SSD striped setup with humongous throughput (600MB/s) made a kernel compilation 1.4% faster compared to using a 5400rpm HD. But then I have 16GB RAM, and RAM is a huge bottleneck in its own right, as swapping or pushing out the file cache will kill compilation times.