Got a question from a relative the other day: "Why are SSDs so much smaller than hard drives?" Here's my layman's response:
A hard disk has several spinning platters. It is one of the most common failure points in a computer because it is a moving part. It's the thing that gets replaced the most in my data center, followed closely by fans. If you eliminate those two failure points, you eliminate a lot of problems. Spinning hard disks also get quite hot due to friction and the motors involved in spinning the platters, and if you drop your laptop while the hard drive is spinning madly at 4500-10,000 RPM, it's likely to get damaged. Hard drives are also noisy, between the noise of the spinning itself and the motors moving the heads.
Solid-State Disks, on the other hand, are perfectly quiet and have no moving parts. However, they are "memory", and not a hard disk. The manufacturing process is completely different and much more expensive per gigabyte at the moment than hard disks, but they also have much, much faster "seek times" since a head doesn't have to be moved by a motor to read or write to a sector. A typical USB flash drive is around $2 per gigabyte today, while a hard drive is around $0.10 (10 cents) per gigabyte (late 2009 prices).
So what are the advantages to having a SSD in your notebook instead of a hard drive?
* Totally quiet
* Creates less heat
* Usually takes less power, resulting in longer battery life
* Less likely to lose data during rough handling
* Higher reliability across the board
* Extremely fast "seek times" looking up data (no heads to move into position first).
* Will get faster/larger in the future for the same dollar due to market demand
Disadvantages vs. a hard drive
* Smaller capacity per dollar
* Despite faster seek times, often no faster on sustained reads than a hard drive
* Limited read/write cycles (typically a few hundred thousand before parts of the SSD are dead, though manufacturers work around this in various ways)
* Cheap SSDs often have far worse performance and power requirements than comparable hard drives (varies by manufacturer)
Eventually, I see a day when virtually all portable computers will ship with SSDs instead of hard drives due to their rapid improvements and dropping prices. And, in truth, a single 20GB drive holds all the "stuff" I use day-to-day. Extra capacity beyond that is music, movies, and other storage-hogging material like my home studio recordings. Basically, at this point whether you go with SSD or a hard drive boils down to "how much storage do I need in my notebook?" which is typically dictated by whether you're big into movies and music on your computer or not.
Good luck in your search!