Storage Devices

 "A Storage device used in the computer to store the data. "

Types of Storage Devices  :

There are three types of storage device. 

1. Primary Storage Device
2. Secondary Storage Device 
3. Off-Line Storage Device

Primary Storage Device  :

Primary Storage Device Also known as main main Memory.

Main Memory is directly or indirectly connected to the Central Processing Unit by a Memory Bus.

The CPU Continuously reads instructions stored, there execute them as required. 

There are three types of Primary Storage. 

1. RAM
2. ROM
3. CACHE

RAM ( Random Access Memory ) :

Random Access Memory is the full name of RAM. It is called Random Access Memory because any of the Data in RAM can be accessed just as fast as any of the other data.

There are two types of RAM  :

1. DRAM - Dynamic Random Access Memory 
2. SRAM - Static Random Access Memory 

and other three types of RAM. 

• SDRAM - Synchronous Dynamic Random Access Memory 
• SSRAM - Synchronous Static Random Access Memory 
• VRAM - Virtual Random Access Memory or Video Random Access Memory 

Difference Between RAM and ROM :

These are the differences between RAM and ROM.

RAM Memory :

1. Random Access Memory 
2. RAM is Volatile 
3. Allow Reading and Writing 
4. Temporary Storage 
5. RAM is Expensive 
6. Perform Read & Write Functions 
7. DRAM & SRAM 

ROM Memory  :

1. Read Only Memory 
2. ROM is Non-Volatile
3. Allow Reading Only
4. Permanent Storage 
5. ROM is cheap
6. Perform Write Function
7. PROM & EPROM

Static RAM : 

1. Faster than Dynamic RAM
2. More expensive 
3. More Power Consumption 
4. Does not need to be referred.

Dynamic RAM :

1. Slower
2. Less expensive 
3. Less Power Consumption 
4. Need to be referred thousands of times per second. 

ROM ( Read Only Memory  ) :

This memory is used as the Computer begins to boot-up.

Small program called firmware are often stored in ROM chips on Hardware Devices  ( like a BIOS chip ) and they contained instructions the computer can be use in performing some of the most Basic Operations require to be operate hardware Devices 

ROM memory can not be easily or quickly overwritten or modified. 

There are four types of ROM :

1. ROM - Read Only Memory 
2. PROM - Programmable Read Only Memory 
3. EPROM - Erasable Programmable Read Only Memory 
4. EEPROM - Electrically Erasable Programmable Read Only Memory 

Cache Memory  :

Cache memory is high speed access area that can be either a reserved section of main memory or a storage device. 

Most Computers today comes with L3 cache or L2 cache, while older computers included only L1 cache.

Secondary Storage Devices:

It is not directly accessible by the CPU.

Computer usually uses its input / output channel to access secondary storage and transfer the desired data using intermediate area in primary storage. 

Example  - Hard Disk 

Hard Disk :

• The hard disk drive is the main and usually largest data storage device in a Computer. 
• It can store anywhere from 160 gigabytes to 2 terabytes. 
• Hard Disk speed is the speed at which content can be read and written on a hard disk. 
• A hard disk unit comes with a set rotation speed varying from 4500 to 7200 RPM.
• Disk access time mesured in milliseconds 

Hard Disk are two types.

1. Internal Hard Disk
2. External Hard Disk

Magnetic Tape  :

Magnetically coated strip of plastic on which data can be encoded.

Tape for computer are similar to tapes used to store music.

Tape is much expensive than other storage medium but commonly a much slower that is commonly use for backup.

Optical Disk  :

Optical disk is any storage media that hold content in digital format and is read using a laser assembly is considered optical media.

The most common types media are 

BD ( Blue - ray Disk )

CD ( Compact Disk  )

DVD ( Digital Versatile Disk  )

CD ( Compact Disk ) :

Capacity  = 700MB

Wavelength = 780nm

Read Write Speed  = 1200kb/Second 

Example - CD - ROM , CD - R, CD - RW

DVD ( Digital Versatile Disk) :

Capacity  = 4.7GB - 17GB

Wavelength = 650nm

Read Write Speed  = 10.5MB/Second 

Example  - DVD - ROM, DVD - R, DVD - R/RW, DVD - RAM

BD ( Blue - ray Disk) :

Capacity  = 50GB

Wavelength = 405nm

Read Write Speed  = 36MB/Second 

Example  - BD - R, BD - RE

Offline Storage :

• Also known as disconnected storage.
• It a computer data storage on a medium or a device that is not under the control of a processing unit.
• It must be inserted or connected by a human operator before a computer can access it again.
• Also known as disconnected or removable storage 

1. Floppy Disk 
2. Zip Diskette 
3. USB Flash Drive 
4. Memory Cards 

Floppy Disk  :

• A soft magnetic disk.
• Floppy disk are portable.
• Floppy disk are slower to access than hard disk and have less storage capacity but they are much less expensive. 
• Can store data up to 1.44MB
• Two common size 5¼ and 3½.

Zip Diskette :

• Hardware data storage device developed by lomega that Functions like a standard 1.44 floppy drive. 
• Capable to hold up to 100MB of data or 250MB of data on new drivers.
• Now it less popular as users needed larger storage capabilities. 

USB Flash Drive  :

• A small portable flash memory card that plugs into a computer's USB port and Functions as a portable hard drive.
• Flash drives are available in size such as 256MB, 512MB, 1GB, 4GB, 8GB and 16GB are an easy way to transfer and store information.

Memory Card  :

• An electronic flash memory storage disk commonly used in consumer electronic device such as digital cameras,  MP3 players mobile phones,  and other small portable device. 
• Memory cards are usually read by connecting the device containing the cart to your computer,  or by using a USB card reader.