memory and storage Flashcards
primary storage
has RAM (random access memory) and ROM (read only memory)
Secondary storage
Includes hard disk drives, solid-state drives
Off-line Storage
CDs, DVDs, DVD-RAM and Blu-ray disks, Flash memory/memory stick
RAM
• Used as main memory in a computer
• This memory is volatile: Temporary memory, requires power to retain the data
• Can be written to or read from the memory
• Used to store data, programs or parts of the
operating system currently in use
• RAM is slower than the CPU cache, but faster then secondary storage
ROM
- non-volatile /permanent memory
- Used to store the start-up (boot up) procedures or BIOS (basic input/output system)
- Can be read from, but not written to
- ROM comes on a small, factory- made chip built into the motherboard
how ROM works
- When the computer is powered on, the CPU reads instructions from ROM
- The CPU perform self-checks and set up the computer: • Test memory is working correctly
- See what hardware is present
- copy the operating system into RAM
secondary storage: HDD (hard disk drive) / magnetic hard disks
• Also called hard disk drive (HDD) – most common method used to store data on a computer
• Data is stored in a digital format on the magnetic surfaces of the disk
• Magnetic fields used to control magnetic
dots of data
• Portable HDDs are popular for backing up and transporting large amounts of data
• Despite their moving part, HDDs are generally very long lasting and reliable
Off-line Storage: optical disks
• Optical discs are cheap and robust secondary storage
• Optical discs such as: CDs, DVDs, and Blu-Ray discs
• Come in three forms: Read-only (eg. CD-ROM/ DVD-ROM/ BD-ROM), Write-only (e.g. CD-R, DVD-R, BD-R)
, Rewritable (e.g. CD-RW/ DVD-RW/ BD-RW
blu-ray discs
- Blu-ray disks are optical media
- Use blue laser light to read and write the data
- wavelength of of blue light is 405 nm (compare to red light wavelength of 650 nm), they can store considerably more data
- Use a single polycarbonate disk (unlike DVDs which use a sandwich of two polycarbonate disks)- Therefore, Blu-ray disks don’t suffer from birefringence (light refraction into two separate beams which can cause reading errors)
secondary storage: solid state drives
- SDD – fast and reliable secondary storage
- Reliable – because no moving parts to go wrong
- Most use NAND chips to control the movement of electrons
- Some use EEPROMs (electronically erasable programmable read only memory) which utilize NOR chips
- SDDs are used for the same purpose as HDDs – for internal storage
- Portable SDDs can be used to back up and transport data
flash memory
- Use solid-state technology
- USB pen drives and memory cards (e.g. SD cards)
- Small and lightweight which makes them ideal for transferring files and photos between different computers
- They used to expand the storage capacity of small devices like cameras, smartphones and tablets (which are too small for SSDs or HDDs).
- Capacity is very high relative to their tiny size
- No physical moving parts
- Should follow the correct removal procedure to avoid corrupting the storage device
advantages of HDD
• HDDs are cheaper. • Both are high capacity, but HDDs are higher. • HDDs have a longer read/write life than SSDs – SSD can only be written a certain number of times before they begin to deteriorate.
Advantages of SSDs
• SSD are faster. • SSDs don’t need defragmenting • SSDs are more shock-proof than HDDs. • HDDs make some noise, SDDs are silent. • Consume less power and also run much cooler than HDDs
Disadvantages of HDDs
• HDDs have moving parts, which can fail.
• Crashes can damage the surface of the disk, leading to the loss of data
• Easily damaged if dropped.
• Uses a large amount of power
compared with others
Disadvantages of SSDs
- SSD have limited storage capacity compared with normal magnetic hard drives
- Random write speeds of solid-state drives can be four times slower than for normal magnetic hard drives.
- The cost per MB stored is higher than for magnetic drives
