1.2 | Memory and Storage

• Primary storage is very quick because it is directly accessed by the CPU.
• Primary storage is typically smaller in storage size.
• Primary storage, often referred to as 'main memory' also includes both the RAM (Random Access Memory) and the ROM (Read Only Memory).
• Secondary storage is slower than primary storage because it is not directly accessed by the CPU.
• Secondary storage is typically larger in storage size.
• Secondary storage is used for the long-term storage of data and files because it is non-volatile.
• Secondary storage includes: magnetic, optical and solid state storage.
• Volatile storage is temporary, meaning that when power is turned off, data is lost. An example is RAM.
• Non-volatile storage saves the data even when not powered on. The data is stored long-term and accessed when the computer is switched on. An example is ROM.
• Primary storage is needed because it is faster than secondary storage devices meaning that instructions and data are able to be copied from the hard drive into the RAM and to be processed by the CPU faster.
• RAM is an example of Primary Storage. It stores all programs that are currently running. RAM is also responsible for storing parts of the operating system to be accessed by the CPU.
• The RAM is made up of a large number of storage locations, each can be identified by a unique address.
• ROM can not be changed.
• ROM stores the boot program / BIOS for when the computer is switched on. The BIOS loads up the operating system to take over managing the computer.
• If there is insufficient space in the RAM, all the programs can use the hard disk drive as an extension of RAM. This is referred to as virtual memory.
• Optical storage is a type of non-volatile storage that uses light to store data. It uses a strong laser beam to melt a sliver coated plastic disk, where a binary 1 represents a small hole and a binary 0 representing no hole.
• Examples of optical storage: CDs, DVDs and Blu-rays.
• CDs can store 700MB.
• DVDs can store 4.7-9.4GB.
• Blu-ray can store 25-128GB
• A disadvantage of optical storage devices are that they can easily be scratched and degrade over time. They have a limited capacity and often have compatibility issues between different formats.
• Magnetic storage is non-volatile storage that stores data through a read/write head moves nanometres above a disk platter using a magnetic field of the platter to read or edit data.
• Magnetic tape is a type of magnetic storage that has a high storage capacity but data has to be accessed in order (serial access). It is used by companies to store large amounts of data.
• Magnetic storage has a large capacity and a cheaper cost per GB than solid state.
• Modern external HDDs (magnetic storage) are small and well protected so they are durable and portable. Though they have moving parts meaning that they should not be moved whilst powered on.
• Magnetic storage has slower access speeds than solid state but faster compared to optical storage.
• Optical storage discs are thin and very portable. They are also very cheap to buy in bulk.
• Optical storage discs have the slowest access speeds.
• Solid State Drives are replacing magnetic hard disk drives in modern devices because they are quieter, faster and use less power.
• Solid State Storage examples: SD memory cards (found in digital cameras), micro SD cards (found in smartphones) and USB flash drive (USB stick).
• Solid State Drives are more expensive per GB compared to magnetic storage.
• Solid State Storage is usually durable but sometimes cheap USB sticks can snap or break.
• The small size of USB sticks (Solid State Storage) means that they are very portable.
• Solid State Storage have a high capacity and the fastest access speeds because of no moving parts.
• 8 bits is equal to 1 byte.
• 1000 bytes are equal to 1 kilobyte (KB).
• 1000 kilobytes are equal to 1 megabyte (MB).
• 1000 megabytes are equal to 1 gigabyte (GB).
• 1000 gigabytes are equal to 1 terabyte (TB).
• 1000 terabytes are equal to 1 petabyte (PB).