Unit A451: Computer systems and programming
Section 2: Computing Hardware 5/5: Secondary Storage Section Objectives
Candidates should be able to: (a) explain the need for secondary storage (b) describe common storage technologies such as optical, magnetic and solid state (c) Discuss the advantages and disadvantages of different types of secondary storage The need for secondary storage
•We all want to store files over a long period of time. We keep photographs, projects, music, films, letters and spreadsheets on our computers. We also expect our programs to be there when we switch the computer on.
(s) explain the need for secondary storage The need for secondary storage
This long term storage is sometimes called Secondary Storage / Memory (primary memory is the main memory)
(s) explain the need for secondary storage The need for secondary storage
Although RAM can store the data and programs used when a computer system is actually running, it is volatile, meaning it loses its contents without a power source.
(s) explain the need for secondary storage The need for secondary storage
Secondary storage therefore needed because it is non-volatile, meaning it retains its contents without the need for a power supply. It also has the large storage capacity needed to store the operating system and all the programs and files needed by a modern computer system. Because we need a lot of it, it therefore needs to be cheap.
(s) explain the need for secondary storage Magnetic Storage
This is the oldest of the technologies and is used in floppy disks, hard disks and tapes. Magnetic disks are read with a moving head inside the disk drive and magnetic tapes are read by moving the tape past a read-write head. •Advantages High Capacity Cheap relative to amount of space •Disadvantages Non Portable, Slow write speed to tape Can be damaged by magnets and wiped easily
(t) describe common storage technologies such as optical, magnetic and solid state Optical Storage
•The word “optical” should make you think about the eye and how we see the world in terms of reflected light. Optical media work in a similar way. They use a surface where a pattern of reflective and non-reflective areas represents the binary data. •Advantages CD drives are common in PC’s and Laptops Easily portable Blu-ray discs are easily layered so can hold massive amount of data •Disadvantages Easily damaged/scratched Quite expensive for re-writable discs
(t) describe common storage technologies such as optical, magnetic and solid state Solid State (Flash) Storage
Solid state devices are a form of flash memory, it is therefore non- volatile like ROM so the contents are not lost when there is no power supply, but able to be written to as in RAM. Solid State Devices can replace the hard drive as the main secondary storage device in a computer, where really large storage capacities are not required. •Advantages Fast read and write times compared to both other types Resistant to shock so highly portable •Disadvantages Low storage compared to other two types Expensive for high capacity storage
(t) describe common storage technologies such as optical, magnetic and solid state Storage Considerations
Capacity: The amount of data to be stored / size of the file. Are you a school pupil wanting to store an essay, or a multinational company with years worth of records? Speed: How quickly the user needs to be able to access the data from the storage device? Portability: Whether the data needs to be moved from one place to another such as from home to school. Some companies store back-ups of important data ‘off-site’. Durability: How long the storage media can reasonably be expected to last? Remember that a lot of secondary storage needs to be portable. Reliability: Whether the data can always be accessed reliably and in the format in which it was saved.
(u) select suitable storage for a given application and justify choice using characteristics such as capacity, speed, portability, durability and reliability. Your Tasks
Task 1 Explain the need for secondary storage in computer systems (4 marks) Task 2 Discuss the advantages and disadvantages of each storage device. For higher marks, compare them to each other. (6 marks)
(u) select suitable storage for a given application and justify choice using characteristics such as capacity, speed, portability, durability and reliability.