A portion of RAM used to speed up access to data on a disk. The RAM can be part of the disk drive itself (sometimes called a hard disk cache or buffer) or it can be general-purpose RAM in the computer that is reserved for use by the disk drive (sometimes called a soft disk cache). Hard disk caches are more effective, but they are also much more expensive, and therefore smaller. Nearly all modern disk drives include a small amount of internal cache.
A soft disk cache works by storing the most recently accessed data in the RAM cache. When a program needs to access new data, the operating system first checks to see if the data is in the cache before reading it from the disk. Because computers can access data from RAM much faster than from a disk, disk caching can significantly increase performance. Many cache systems also attempt to predict what data will be requested next so they can place that data in the cache ahead of time.
Compression is the reduction in size of data in order to save space or transmission time. For data transmission, compression can be performed on just the data content or on the entire transmission unit (including header data) depending on a number of factors.
Content compression can be as simple as removing all extra space characters, inserting a single repeat character to indicate a string of repeated characters, and substituting smaller bit strings for frequently occurring characters. This kind of compression can reduce a text file to 50% of its original size.
Decompression of file archives can be achieved on all computers, but live decompression of video requires much more powerful hardware.Decompressing image files does not require significant amounts of processing power and so it can be done on-the-fly.
Free online backups allow you to store backups of your files offsite. If any disaster should occur at your location (perish the thought), at least you can still access the backup copy of your files since it's probably kept in a different part of the country (or even world - depending on where you are relative to the service). You can then access your files and even share them from anywhere. Some of the services allow you to automatically schedule backups, and keep different versions (or generations) of your files, so, if for example, if you are working on a file all day, and find that you deleted an important section of your document in your latest "save", you can recover an earlier version of the saved and backed up file (something like version control software except that this is primarily a backup solution). Some, if not all, of the backup solutions also encrypt your files, hopefully making it inaccessible to anyone except those with a password.
Optical Disk Drive
A storage medium from which data is read and to which it is written by lasers. Optical disks can store much more data -- up to 6 gigabytes (6 billion bytes) -- than most portable magnetic media, such as floppies.
Solid-state storage
Solid-state storage is a nonvolatile, removable storage medium that employs integrated circuits (ICs) rather than magnetic or optical media. It is the equivalent of large-capacity,nonvolatile memory. Examples include flash memory Universal Serial Bus (USB) devices and various proprietary removable packages intended to replace external
external hard drive.
The main advantage of solid-state storage is the fact that it contains no mechanical parts. Everything is done electronically. As a result, data transfer to and from solid-state storage media takes place at a much higher speed than is possible with electromechanical disk drives. The absence of moving parts may translate into longer operating life, provided the devices are reasonably cared for and are not exposed to electrostatic discharge.
