1) What to look out for when contemplating SSD replacement for existing HD
The first things to look out for would be the interface and form factor. SSDs are only available with SATA interfaces, and to achieve maximum benefit you'll want to install one in a system having a 6Gbps (600MBps) internal SATA interface. If the interface is limited to 3Gbps (300MBps) then that will limit drive performance to about half of what it would otherwise be capable of. If the interface is SATA 1.5Gbps (150MBps) then I would recommend not spending the money on an SSD, and would recommend a fast but much more economical hybrid drive like the Seagate Momentus XT
Next is the form factor. The SSDs I recommend
come in a standard 2.5" drive form factor and are 7mm or 9.5mm thick, either of which should fit in most 2.5" laptop bays. The "boxed" (retail packaged) versions of these drives also normally include a 3.5" bay adapter for installation in conventional desktop 3.5" drive bays. SSDs are also available in 1.8" or mSATA form factors for systems using those form factors as well.
Finally an issue related to both SSDs as well as newer Advanced Format (4K sector) HDDs is partition alignment. For optimal performance you'll want to insure that all partitions are aligned to even 1MB boundaries. Windows Vista and later automatically create 1MB aligned partitions, but if you are using XP you'll want to either create the partition(s) in advance on a system running Vista or later, or use a 3rd party partitioning program instead. For more information on this see the sections titled Advanced Format (4K Sectors) and Partition Alignment in URPCs 20th or later editions chapter 9 (Hard Disk Storage).
2) How to handle the defragmentation requirement in SSDs vice standard HD
There is no defragmentation requirement for an SSD, in fact you'll want to turn any automatic defragmentation (such as that built-in to Windows) off, as doing any defragmentation will not improve performance and will only cause unnecessary wear on the flash memory cells. Windows 7 or later will automatically disable defragmentation for any SSDs that are installed, you'll have to reconfigure XP or Vista manually to disable defragmentation (or in some cases use a utility to do that for you).
Another related issue for SSDs is the internal use of the TRIM command, which informs the SSD about deleted files in the file system allowing for greatly improved "garbage collection". SSDs can only write to erased blocks, and garbage collection is the process by which an SSD will internally consolodate used blocks and erase unused blocks in advance of future writes, allowing for a high level of write performance to be maintained. Without TRIM the drive will believe deleted files are still in use, and will not be able to consolodate and erase those blocks. Windows 7 and later automatically invokes the TRIM command when deleting files, allowing for much more efficient garbage collection to take place.
When using an SSD under XP or Vista, additional software provided by the SSD mfr. can handle issues such as OS reconfiguration/optimization and TRIM. For example the Intel Solid-State Drive Toolbox
will automatically reconfigure Windows XP and Vista by disabling any automatic defragmentation, turning off Superfetch/Prefetch and ReadyBoost, and performing TRIM either on-demand or on a predetermined schedule. A utility like this allows SSDs to operate just as well under XP or Vista as they would under Windows 7 or later.
3) How to tell if SSD is indeed working properly
Utility software included with the SSDs I recommend (such as the aforementioned Intel SSD Toolbox) can run diagnostic scans as well as read the SMART data from the drive, telling you the overall drive health and life expectancy. Other than that since SSDs act like HDDs as far as software is concerned you can use most HDD test programs as well.
4) If you cover these questions in your U&R books, in which?
I have a new video segment covering SSDs vs. HDDs in the DVD included with my new URPCs 21st edition
book! That book just shipped off to the printer *yesterday* and should be available in a couple of weeks. There is also additional coverage of SSDs in chapter 10 (Flash and Removable Storage) over the existing coverage in the 20th edition. If you have any additional questions I'd be happy to try and answer them here. Scott.