I've heard that Macbook air saves more power and boot time is very short and it is pretty fast in boot time. I know that instead of HDD it uses flash memory but how can it save more power and boot faster?
There are a number of benefits to flash memory over HDD:
- No moving parts
- No spin up time
- No electric motor using your battery charge
- "Seek Time" isn't really a thing, since there's no drive head moving to read a different sector of HDD platter
During boot, your computer reads a lot of software from your boot volume into memory. The time it takes to do this is drastically reduced when using a SSD (flash) instead of an HDD.
An SSD (flash memory) uses less power, so battery life tends to increase (additionally, a Macbook Air uses less power than most other computers in general, which also helps battery life).
Additionally, a SSD is much faster. There are two important methods of accessing data on a drive - sequential and random access. Sequential access is when you are accessing a large amount of data in the same spot (a movie, for example). Hard drives are best at this, though SSD's are still a few times faster (2x-5x, depending on the drives in question - the one in the Macbook Air will tend towards the lower end of this range).
Random access is when you are accessing data that is stored in small amounts all across the disk. Here, SSDs are much better than conventional hard drives (20x-100x faster). This is because there is basically no seek time for SSDs (there is no spinning disk). Seek times are what slow conventional hard drives down so much. This sort of access is common when booting up, launching applications, and switching between applications, which is why the Macbook Air boots quickly and will generally feel faster than its other tech specs would suggest.
In short, an SSD provides a massive performance boost over a normal hard drive. The only issue is that they tend to be expensive, which is less of an issue with the Macbook Air (though it does explain why the hard drive in the Macbook Air is so small).