Reducing Kernel BootUp Time

The kernel boots rather quickly, even with no attempts to make it go faster. In the example later in this chapter, an unmodified kernel for a 400Mhz arm board boots in about seven seconds from power-up, and three of those seconds are spent by the boot loader waiting for the user to interrupt the boot process (the measurement was done on a device still used for development). This means the device is ready to run user programs in about four seconds. This also means speeding up the kernel boot process is a series of changes that reduce the speed in the quarter- to half-second range; with effort, you can reduce the time to about two or three seconds, which is in the range of a digital camera.

Also notice that the choice of root file system is the largest predictor of boot time for the kernel. In the example, using a JFFS2 file system takes a breathtaking six seconds to mount for 50MB flash storage. When using a read-only file system, the mount time is in the subsecond range. If you need to have a large, solid-state drive, consider getting hardware that has flash memory that appears as though it's a standard block-based device, similar to a USB memory stick.

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Digital Camera and Digital Photography

Digital Camera and Digital Photography

Compared to film cameras, digital cameras are easy to use, fun and extremely versatile. Every day there’s more features being designed. Whether you have the cheapest model or a high end model, digital cameras can do an endless number of things. Let’s look at how to get the most out of your digital camera.

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