chapter 5-2
Secondary storage
he term secondary storage is sometimes used to describe devices that can store data permanently, such as a hard drive, flash drive, compact disc, DVD, or external hard drive. This is because the computer will look for data on one of these devices if the data is not in RAM.
Sequential storage device
A random access storage device lets a computer go directly to the needed information. The device does not have to search the entire medium to find data. For this reason, random access storage devices are much faster, and more expensive, than sequential devices. A hard drive is an example of a random access storage device.
Primary storage
The term primary storage is sometimes used to describe the main memory, or RAM, in a computer. This is because when the CPU needs data or instructions, it looks in memory before looking anywhere else. Most knowledgeable computer users, however, avoid using the term storage when talking about RAM. This is because RAM works very differently from storage devices such as disks or flash drives. RAM also loses any data it contains when the computer is turned off, while disks and flash drives can hold data permanently.
Random access storage device
When equipped with a tape drive, business computers can store data on a long piece of tape, similar to an old-fashioned cassette tape. A tape drive is an example of a sequential storage device, which requires the computer to scan from the beginning of the medium to the end until it finds the data it needs. While cheaper and slower than other types of storage, the highest capacity tape cartridges can hold five terabytes of uncompressed data.
read-only device
A read-only device can only read data from the storage medium. You cannot change the data on the medium or save new data onto it. A CD-ROM drive is an example of a read-only device, because it does not have the capability to write data onto a disc. The media used with read-only devices come with data already saved on them. Music CDs or software programs on CDs are CD-Rs. Your CD-ROM drive will be able to play the music or read the program instructions from the disc, but you can't change the disc's contents. Standard DVD players are another example of a read-only device.
Read/write device
A read/write device not only can read data from the storage medium, but can write data onto the medium, as well. These devices let you read data from a disk or tape, make changes to the data, and save new data onto the medium. Hard drives, USB flash drives, CD-Rewritable drives (CD-RW), and DVD-RAM drives are commonly used examples of read/write devices.
Optical storage device
Magnetic storage devices are specially treated disks or tapes, such as those mentioned above, that record information using magnetically sensitive materials. These devices use electricity to shift magnetic particles so they form a pattern that the computer reads and stores as information. Common magnetic storage devices include hard drives and tape drives. Other storage devices use laser beams to read information that has been stored on the reflective surface of a disc. These are called optical storage devices. Popular types of optical storage devices for computers include CD-ROM and DVD-ROM drives.
Archival storage device
The term secondary storage is sometimes used to describe devices that can store data permanently, such as a hard drive, flash drive, compact disc, DVD, or external hard drive. This is because the computer will look for data on one of these devices if the data is not in RAM. Many kinds of secondary storage devices can hold much more data than a computer's RAM can. For example, while most of today's PCs have from 4 to 16 gigabytes of RAM, they have hard drives that can store up to a terabyte. Because they can store data permanently (or until you erase it), secondary storage devices are sometimes called archival storage devices. This refers to the fact that you can store data on a drive or disk and then put it away for a long time, only using it again when you need it.