There are two types of storage systems in terms of computers:
> Primary storage: is the storage provided by memory in a computer
> Secondary storage: storage provided by peripheral devices other than memory
Memory – The amount of memory in a computer system determines the level of complexity of task that the system can handle. A single unit of memory is called a bit. A bit can store 0 or 1. Eight bits together are called a byte. Memory, and data storage capacity is usually measured in larger units.
There are two classes of memory in a computer system:
> Ram: (random access memory)
> Rom: (read only memory)
RAM is memory that can be both read and written to. It is used for storing data and programs while the computer is being used. Most RAM is volatile, i.e. it can only hold data while power is supplied to the computer. Once the power is turned off the contents of ram are lost. System settings such as date and time are stored in CMOS (complementary metal oxide semiconductor) RAM. CMOS RAM has a battery to keep the data. Therefore the data is not lost when the main power to the computer is closed.
The main part of RAM may either be static or dynamic.
> Static RAM is more expensive but allows for faster transfer of data
> In dynamic Ram, the contents will “decay” even when the power is on, and so needs to be continually refreshed which slows down your computer.
ROM: Read only memory contains the start up sequence for a computer system, this will also include the BIOS. Once the computer is switched on the BIOS will load up the rest of the operating system to allow the user to use the computer.
The data in ROM cannot be altered or deleted, unless it is erasable and reprogrammable (EPROM) however this can only be reprogrammed a fixed number of times before it wears out. ROM is also non-volatile.
A buffer is an area of memory used for holding data during input or output transfers to and from input/output devices. Because the CPU can process data thousands of times faster than a printer can print, input and output are handled independently. Once an input/output operation is initiated, a special input/output channel takes control of the operation, leaving the CPU free for other tasks.
Information that is to be printed is placed in a print buffer, which may be several megabytes long, located wither in the computer or the printer, or both. E.g., a laser printer has its own memory buffer.
For transfer of data to and from peripherals, some very fast RAM is often used. This is known as cache RAM. In a computer system with a large cache, data transfer times to and from input/output devices is very short. The greater the amount of cache, the better, however this also adds to the cost of the computer.
These are a cheap type of storage device that plugs into a parallel port of a PC. They consist of a single removable drive with the same diameter of a standard floppy disk (3.5inches) The zip disks looks like a standard floppy disk, however it is much faster. The typical storage amount of a zip drive is 250mb. Its transfer rate is around 1.7Mb per second.
The hard drive is the main storage device of a computer. Your applications, games and everything else are stored here. Hard drives are big, fast and are stored onto the computer. The speed at which your computer boots up and programs loads is totally related to the performance of your hard drive.
They are more secure and reliable than floppy’s. Hard disks hold more data and are faster than floppy disks. A hard disk, can store anywhere from 10 to more than 100 gigabytes, whereas most floppies have a maximum storage capacity of 1.4 megabytes. The hard disk is capable of holding large amounts of data and it has a very high data transfer rate.
Floppy disks are an important type of storage device. They have a low storage capacity (1.44mb), which means they are only suitable for transferring small files between computers as well as providing a back up for word-processing documents.
Floppy disk facts:
* They are normally called 3-1/2 inch floppy disk.
* They are able to store 1.44MB of memory
* There is a small switch on the bottom right hand of the floppy disk to see if the disk is only read-able or write able.
Advantages of floppy disks: –
* They are cheap
* Very portable, and therefore can be used to pass a small amount of data from one system to another.
* They are very powerful, for example, through floppy disks you can access MS DOS.
Disadvantage of floppy disks: –
* They are not continually rotating like a hard drive, so the disk has to accelerate up to the operating speed before the data can be read off or written off.
* The disk holds a limited amount of data and has a relatively slow data transfer rate.
This is the most common form of an optical disk. When disks are supplied, with the data already written on them it is called CD-ROM. CD-ROM’s are much faster than a floppy disk but slower than a tape of hard disk.
They are used:
* To distribute software
* To distribute information, for example, encyclopaedias and directories.
* Backup – keeping copies of important data.
There are many different CD-ROM drives available, each with a different multiplier, example 40-speed, 48-speed. This is the speed in which the CD is able to transfer its data, which is called the transfer rate.
CD-R drives use disks that can be written once and never again. They can be read by any CD-ROM drive. CD-R discs usually hold 74 minutes (650 MB) of data, although some can hold up to 80 minutes (700 MB). With packet writing software and a compatible CD-R drive, it is possible to save data to a CD-R in the same way you can save it to a floppy disk.
CD-RW is a type of CD disk that enables you to write onto it in multiple sessions. CD-RW drives are readable and write able. This means that the information written on them today can be overwritten with new information tomorrow. Also, they can be read by any CD-ROM drive. CD-RW drives are very important because they allow you to share large amounts of data with other people.
With CD-RW drives and disks, you can treat the optical disk just like a floppy or hard disk, by writing data onto it multiple times. CD-RW disks can be rewritten as many as 1000 times.
In magnetic tape, data is recorded in frames across the tape, with one frame representing one byte. The frame forms tracks along the length of the tape. Magnetic tape is a serial medium, which means that if you want to find an individual record you have to access it by starting at the beginning of the tape and reading through every record until the required one is found. Magnetic tape is cheap and convenient for backing up data as back ups are rarely used. Also they are considerably cheap compared to the amount of data they are able to hold. An average 7GB can be bought for under 10.00.