Data Storage

• Primary memory is directly accessible by the CPU. Secondary storage data must be loaded into RAM before it can be used
• RAM is the working area of the computer where currently used data is temporarily stored
• ROM contains data that can’t be changed and needs to be stored permanently such as start-up routines
• DRAM consists of transistors and capacitors. It needs to be refreshed constantly but has a high memory capacity and consumes less power. Main memory is constructed from DRAM
• SRAM uses flip flops to hold bits of memory. Doesn’t need constant refreshing and has a faster data access time than DRAM. CPU cache memory makes use of SRAM. More expensive to manufacture
• Magnetic Storage Devices such as HDDS store data on platters coated in a magnetisable material. These platters spin quickly and read/write heads float above their surfaces to permit reading and writing of data. Both sides of the platter are used and there are many platters.
• In HDDS data is stored in sectors and tracks. The read/write heads move constantly to find blocks of data, and the time this takes is called Latency. Data on a HDD can suffer from fragmentation
• SSDs operate by controlling the movement of electrons in NAND or NOR chips. Data is stored in binary on millions of transistors.
• At each junction in a NAND matrix there is one floating gate and one control gate. When voltage is applied to the control gate, electrons are attracted to it and get stuck in the floating gate - giving control of the bit value stored at each junction
• Memory sticks, flash memoris, SS cards and SSDs use solid-state technolog and they are more reliable, faster and consume less power than HDDS
• Optical storage devices, like CDs, use red laser light to read/write data on the disk’s surface. Their surface is coated in a light alloy or light-sensitive dye. Data is stored in pits and lands which can be read by an optical head.
• Blue-Ray disks use blue instead of red laser light to read/write data. Since the wavelength of blue is shorter, this increases storage capacity. They also have built in encryption, more interactivity and faster data transfer
• Virtual Memory is the RAM plus swap space. It gives the illusion of unlimited RAM by moving pages of data to and from HDD/SSD. Memory mapping is used to keep track of memory locations during this process
• With virtual memory programs can be larger than RAM and still executed and it reduces the need to buy more RAM
• However, with virtual memory, disk thrashing can become an issue. This is when so many heads are moving in a HDD that a thrash point is reached where very little execution is being done as the system is too busy moving data
• Cloud storage is storing vast quantities of data on remote physical servers. Have capacities of up to an exbibyte of data
• Public Cloud - When the client and cloud storage provider are different companies
• Private Cloud - a dedicated system behind a firewall where the client and storage provider operate as a single entity
• Hybrid Cloud is a combination of public and private cloud provide where the most sensitive data is stored on the private cloud