Most of them. It is typically netbooks, which are smaller and mainly for internet, that do not have CD/DVD drives.
As many as needed. In laptops/notebooks there is usually only one hard disk. In a desktop or server there could be potentially any number of disk drives. If you mean a CD/DVD drive the same applies.
USB Ports enable use of External Devices such as Wireless Network Cards & Hard drives on Notebooks.
No. None of the models of MacBook Air have CD drives.
Yes, their cd drives are very good.
No. CD drives are only capable of reading CDs, not DVDs. Most DVD drives can read CDs as well.
don't leave cd's and floppys in the drives if they are important.
Yes, Dell notebooks come with recovery CD's. These CD's include whatever operating system you have installed and all of the programs you purchased with your laptop bundle.
Most do, but some do not.
There are a wide range of CD drives available for purchase. Some of the more familiar brands of CD drives are Samsung, LG, Toshiba, Dell, Asus, Sony and Yamaha.
One can buy dvd cd drives online through sites such as Amazon and eBay. Stores like Staples and Best Buy also sell dvd cd drives. Target and Sears, some locations, also sell dvd cd drives.