Memory and Storage Media

Memory, Storage Devices and Media

In this section we will look at different types of memory, the advantages and disadvantages of several storage devices and how media is digitally saved.

PRIMARY, SECONDARY AND OFFLINE STORAGE

The storage devices inside, and outside of a computer fall in to the following categories

PRIMARY STORAGE	This is the storage that is inside your computer and has direct access to the CPU. It includes RAM and ROM. Primary storage is needed to boot up your computer.
SECONDARY STORAGE	Secondary storage is still inside your computer but doesn't have direct access the CPU. This includes HDDs and any internal SSDs you have. They may contain your operating system and important files but technically you could boot up the computer without them. They do not have direct access to the CPU. For example, anything that is saved on your HDD first has to go through your RAM.
OFFLINE STORAGE	This is any storage medium which is inserted in to a storage device to be able to save data. For example, a CD/DVD/BLU-RAY, external hard drive, backup tape etc.

ROM CHIP

ROM stands for Read Only Memory. The ROM chip is inside your computer when you buy it and contains all of the data needed to start your computer. For example, the ROM chip contains the BIOS (Basic In-Out System) which controls the basic devices on your computer needed to boot up. You cannot start your computer without it and you cannot delete the contents of it, hence it being 'read only'

The ROM chip counts as primary storage as it is inside your computer AND needed to boot up. If you didn't have a ROM chip you wouldn't be able to start the PC as it contains important information about the hardware. For example, it decides which hard drive you will boot up from.

RAM

RAM (random access memory) is integral for a computer to perform the most basic functions. RAM is used to temporarily hold data that the computer needs but that isn't yet permanently saved on the hard drive. A CPU performs thousands of calculations per second, but it cannot store all of the answers to these calculations once it has completed them. RAM is used to store the results of the calculations and hold data before it is actually passed to the CPU. For example, let's say that you open the calculator on your computer and type 5+5. The numbers and the operator you chose are stored on the RAM. They are then passed on to the CPU to be calculated. The CPU then passes the calculation back to the RAM and it is displayed on your screen.

If you decide to save a document you're working on, the data will be passed from the RAM to the hard drive for permanent storage. Otherwise it will be deleted after you have closed whatever application you had open. RAM is volatile memory which means that once you switch the computer off, it is cleared.

HARD DISK DRIVES

Unlike RAM, a hard drive is non-volatile storage. This means that after the power is switched off the computer, the data remains on the memory. Hard drives are mamagnetic fields. A read/write head magnetises parts of the platter. Whether a part of the platter is magnetised signifies whether it is a 0 or a 1. Hard drives are very useful for permanently storing data. However, since they have moving parts they are prone to breaking. They are also quite slow to read and write compared with solid state drives (SSDs).

SOLID STATE DRIVES

A solid state drive (SSD) is like a regular hard drive in that it is a permanent non-volatile memory storage medium. The difference is that SSDs do not have any moving parts or platters. The memory on an SSD is stored on a series of chips. The chips hold data by utilising a series of floating NAND gates. Whether the gate is open or closed determines whether it represents a 0 or a 1. Solid state drives are very expensive at the moment and do not have the capacity of hard disk drives. They are however very fast in terms of how quickly they can read/write.

FLASH DRIVES

Flash drives are also known as memory sticks and are a form of chip=-based memory which work on the same principle as SSDs. They are generally smaller in capacity than SSDs and HDDs, usually being sold in 1gb-64gb sizes. They are handy because of their size and portability. They plug directly in to the USB drive meaning that the computer does not have to be taken apart. They are available in USB 2.0 and USB 3.0 which is a faster, newer method of storing the data.

EXTERNAL FLASH HARD DRIVES

External Flash Hard Drives are larger versions of USB memory sticks are are usually used to hold more information than USB sticks are capable of. They are still portable and outside of the computer meaning they are useful for transferring data between systems. The disadvantage is that even with USB 3.0 they are slower than SSDs. They are however cheaper and this has made them very popular.

CDS, DVDS and BLU-RAY

CDs, DVDs and Blu Ray discs are known as 'optical media'. This is because the data on them is read by a laser. CDs are made from plastic and have a thin layer of aluminium sprayed over the top during production. Around the inside of the CD are small tracks which are slightly bumped up over the rest of the surface. These bumps make up the data stored on the disc. The laser reads the pattern of the bumps which correspond to 0s and 1s. Blu Rays and DVDs work in a similar way but have a higher capacity than tradtional CDs. There are several different types of CD and DVD.

CD-R - This is a CD which can be written to but only once when you purchase it. A red laser is used to read and write all forms of regular CD.

CD-ROM - A read only CD which cannot be written to at home.

CD-RAM - A CD which can be read and writted at the same because of a special read-write head. It contains data on concentric tracks.

CD-RW - A CD which can be written to and then erased and re-written.

DVD-RW - A DVD of the minus type which can be rewritten by a drive which works with minus DVDs

DVD+RW - A DVD of the plus type which can be rewritten by a drive which works with plus DVDs

DVD-RAM - A special type of DVD which can be written to and read from far more times than a regular DVD

Blu Ray - Unlike the CD, the Blu-Ray uses a special blue laser to read the data which is much narrower and means that the disc can hold more information.

To increase the capacity of discs, many DVDs and Blu Rays are now multi-layer which means that they have a second layer of 'bumps' behind the first one which doubles the storage capacity of the disc. However, they need a special DVD reader to read the second layer.

DVDs were very popular years ago as they had a very high storage capacity than other types of media around at the time. However, they have now been overtaken by flash drives since they can hold more data. Also, DVDs often take a while to save the data on to them, and can get scratched easily rendering them useless.