Energy breakdown

Table V gives the energy breakdown by hardware for the systems targeted when they are idle and while performing the aforementioned DCT computation. It also gives the one-second energy consumption in EU for different components. The LCD energy is obtained by comparing the system energy before and after the LCD is turned off. Front-light energy is obtained in the same way. ``Others" refers to the system energy minus the LCD and front-light energy. It includes the energy consumed by all other hardware. The table shows that the front light and the TFT LCD consume a large fraction of system energy. The percentages are larger than those reported for notebook computers [4], in which a hard-disk, system-on-board and more powerful processor are used instead of Flash memory and SOCs.

Table V: System energy breakdown for the handheld computers

Handheld		LCD		Front light		Others		EU
	%	EU	%	EU	%	EU	$\mu$Joule
iPAQ1	idle	9	18,800	73	147,100	18	35,300	8.0
	DCT	7		53		40	112,600
iPAQ2	idle	14	20,600	53	77,700	33	48,200	9.8
	DCT	9		34		57	129,100
Zaurus	idle	11	25,200	80	180,000	9	19,000	9.3
	DCT	8		59		33	99,300

With the front light turned off, the TFT LCD consumes from 14% to 55% of the system energy, depending on how busy the CPU is. However, it should be noted that in interactive application usage, the CPU is idle most of the time.