There are a number of reasons: 1. Hardware Hardware is a big problem for boot times. Most hardware is poorly standardized, or not standardized at all, or does

There are a number of reasons: 1. Hardware Hardware is a big problem for boot times. Most hardware is poorly standardized, or not standardized at all, or doesn't even follow the standards, or tries to be backwards compatible with older hardware, or is just plain buggy. This means that the initialization code has to poll and retry and work around a whole bunch of things just in case the hardware happens to be slow in responding or gives a weird response. This is the main reason why POST is so godawful slow, and why the initial linux boot sequence takes so long. Apple hardware can boot quicker because they control what hardware is in the machine and can optimize their initialization code for it. 2. Software The operating system stack is HUGE. There's a LOT of state that needs to be initialized, and most of it is not very efficient (we tend to optimize the runtime operation vs the startup operation of a software package). You absolutely could cut the software component of an OS boot sequence by an order of magnitude, but the development costs would be massive, and the gains pathetic in terms of the work-over-time the machine will do over its lifespan. 3. Protocols A large number of the protocols we use for inter-process and inter-device communication have poorly designed latency characteristics. Either they are too chatty (requiring multiple messages back and forth to do a task), or have ill-defined timeouts (requiring clients to wait longer than they should), or ambiguous states, or some poorly built implementation has become the de facto standard. This is an area I'm personally tackling. 4. Formats We use a number of formats for the wrong kinds of things. Appending to a tgz file, for example, has horrendous time implications, especially as the archive size grows.