A-Level Computing#BristolMet Session Objectives#7 MUST describe common secondary storage technologies SHOULD explain the need for secondary storage and the use of buffers and interrupts in the transfer of data. COULD select and justify suitable storage devices/media for given situations Create coded messages converting decimal to binary.

A-Level Computing#BristolMet Secondary Storage We know that primary storage consists of both RAM and ROM. The RAM (Memory) is volatile and is wiped when the power is turned off. ROM is NOT volatile BUT IS read-only, therefore it can only store preloaded instructions (the boot strap program, for example) and nothing else can be saved on to it. We dont want to have to rewrite programs and data each time we want to process something, therefore a computer needs the ability to store data when the power is turned off SECONDARY STORAGE is the additional storage facility added to a computer system to store data and programs when the power is switched off.

A-Level Computing#BristolMet Storage Media These are the materials which hold the data whereas a storage device is the hardware which reads or writes on to the media. THINK of media as a CD and the device is the CD player. STORAGE MEDIA is grouped into 3 types: 1.Magnetic Hard Disk 2. Optical Disk 3. Flash Memory (Solid State Memory)

A-Level Computing#BristolMet Storage Investigation Use the internet to research and investigate the characteristics of the different types of storage media and then attempt to answer the following questions: 1.State which type of secondary storage is most appropriate for use in the following situations. Give reasons: a)Storing tracks on a MP3 player b)Transferring work from a school computer to home c)Distributing a movie d)As the storage area on a school network.

A-Level Computing#BristolMet Storage Media Magnetic Hard Disk The magnetic hard disk is a magnetised rigid plate or stack of plates with heads to read the data as the platter spins around. It is a reliable and cost effective way of providing high capacity storage at a low cost. The devices can be internal HDDs (Hard Disk Drives) or portable external HDDs which can be used to transfer or back up large amounts of data. Optical Disk The CD and DVD use light from lasers to detect reflections from the data area on the CD/DVD surface. The ROM version is obviously read only, whereas RW (rewritable) can have data written (or burnt) onto them. They are low capacity ( 700MB for CD & 4.7 GB for DVD) and cheap BUT they are also quite slow at transferring data and less reliable as they are prone to damage, either by direct sun light or physical damage such as scratches.

A-Level Computing#BristolMet Storage Media Flash Memory (Solid State Memory) Solid state flash memory has much quicker access times than magnetic disks and are more reliable, as they have no moving parts which means they are less prone to damage through knocked or dropped. It is however comparatively more expensive than magnetic storage and are therefore only used in smaller, more affordable sizes, such as flash memory sticks or as SSHDs for notebooks and slim line laptops (This is also because they can be smaller in size as they do not need room for a rotating disk(s).

A-Level Computing#BristolMet Data Transfer Data transferred from memory to other devices, printers, hard disks etc through the use of buffers and interputs. Buffers are used to store data sent from main memory where it waits until used by the device (either written on disk or printed, for example). This frees up the processor to carry on with other processes. Buffers are only quite small so more data may need to be fetched from memory to finish off the job. This is done through the use of interrupts. Interrupts are requests sent from a buffer to the processor asking for more data to be sent to complete a particular job. The processor must then stop what it is doing and complete the request.

A-Level Computing#BristolMet Data Transfer Processor Buffer Devices, HDD, printers, mic, web cam Write Read DATA INTERRUPT Buffers are generally regions of physical memory found in peripheral devices but can also be allocated to RAM by software, creating virtual data buffers.