Secondary Memory:
Memory that keeps it's data even when power to the device is lost. A PC's hard drive is referred to as it's primary storage. Storage mediums like USB's are known as secondary memory.
Storage Devices:
1. Hardrive disks:
- Traditional PC has at least one hard disk drive holding the OS.
- These devices are magnetic and non-volatile.
- Devices consist of a platter(metal disc) and a read-write head that floats on a cushion of air.
- All data is addressed to the head can move directly to the location where the wanted data is located.
2. Floppy disk:
- magnetic storage devices
- Requires a ploppy reader with a head similar to those of a hard disk drive.
- The last popular size for floppy disk was the 3.5 in, which refers to the size of the plastic housing. The disk could only store 1.44 MB and was popular from the early 1990s to the mid-2000s.
3. Tape Drives:
- Magnetic storage device
- Useful for backing up systems.
- Tape drive stores data on tapes.
- the tape is removed and replaced when it's capacity has been reached.
- Tapes are favored because of their affordability, reliability, low power consumption and portability.
- Tapes can be damaged by fluids or heat but are more reliable than most storage devices.
- A drive may store up to 10 TB at a time. This information is ready to be read and enterprise-sized libraries of drives can store petabytes (thousands of terabytes) of data that can be accessed and loaded robotically.
4. Optical discs:
- Compact discs or digital versatile discs are optical storage mediums used to store audio and video material.
- CD-ROM are discs that are read-only - data is preloaded.
- CD-R and DVD-R are discs that can be written once, and then would only be read-only
- CD/DVD-RW can be written repeatedly.
- CD's typically hold 700MB of capacity, and DVD's 4GB and can have two layers.
- Today, DVDs have been superseded by Blu-Ray discs. Blu-Ray technology allows a disc to have a greater storage capacity of 25 GB per layer. The laser used to read the disc is blue rather than the red used with CDs and DVDs.
5. Flash memory
- Solid-state (No mechanical parts, electronic circuit read and write) non-volatile memory devices.
- Hardrives and other peripherals may contain flash chips, they are useful for storing information like BIOS(Basic Input and output system) that is needed for a computer to boot up.
- BIOS chip is fixed to the motherboard but can be rewritten.
- Flash memory is read much faster than it's written
- It's reliable for up to 100 000 erase cycle after it becomes unreliable.
- The combination of durability, speed, price, and capacity makes flash memory an ideal storage medium.
6. Flash USB drives
- plug and play- which means it can be used as soon as its plugged in. No drivers needed.
- Contains flash memory, USB port and a controller which controls the read and writing of the chip.
- The efficiency of the control determines the speed at which the device can operate.
7. Memory cards
- Form of flash memory
- Commonly found in portable devices such as mobile phones and cameras.
- Can have a capacity anywhere from 4Gb to over 2TB.
8. Solid-state drives
- Form of flash memory
- Has no mechanical parts.
- Commonly found in laptops and computers.
- data can be directly accessed because it's a digital form.
