Memory is a topic that often confuses people. I have many times heard people saying that they don't have enough memory to store all their photos. Whilst in a generic sense they are quite correct, it creates confusion at a more detailed level when addressing specific problems or evaluating computing needs.
Memory as a generic term has a number of categories. Disk, Card, RAM & ROM, SSD, USB stick. This article will explore the definitions of each of these and outline their uses.
Random Access Memory (RAM)
RAM is used by computers as temporary storage of data whilst processing. It provides both calculation space and storage of data being used by an application. RAM is the fastest form of memory and until recently was limited in capacity. Newer machines now have capacity for up to 32Gb of RAM.
When there is not enough RAM for active processes the computer makes use of free space on the hard disk. This is called virtual memory. On most Windows systems it is allocated automatically by the Windows OS, but it can be manually configured. Virtual memory is a lot slower than RAM, so if your computer is continually running out of RAM the performance will be slow. If your hard disk is fragmented or nearly full this will slow performance even more.
There are two type of RAM: Dynamic (DRAM) and Static(SRAM). DRAM is most common in computers. It is cheaper than SRAM but slower (access time of 60 nonseconds vs 10 nanoseconds). RAM loses its content (volatile) when the machine is turned off.
Read Only Memory(ROM)
ROM is a type of RAM but cannot be written to. It contains static content which is predominently used to store the programs which boot your computer. Generally ROMs store only a few thousand bytes. ROM keeps its content even after the machine is turned off.
Hard & floppy disk drives
Hard drives are the main storage on most computers, although some small laptops and of course tablets use SSDs (see below). The main hard drive contains the operating system and application files. Computers can have a number of physical hard drives which can be divided in to a number of logical partitions. For example many computers two partitions on their main hard drive, the boot disk containing the operationg system and program (c:) and a recovery drive (q: or another letter) used to restore c: in the advent of a crash.
Floppy disks are removeable disks, now outdated technology. They have been replaced by CDs and most recently by USB drives.
Solid State Drive (SSD)
SSDs are currently the fastest storage devices available. They, unlike hard disks, have no moving parts. They are made up of DRAM boards (or EEPROM), a memory bus board, their own CPU and a battery card.
Solid state drives have a performance that is several times greater than that of hard disks, but have a shorter lifespan and are considerably more expensive. In contrast to hard disks, there is a performance difference in SSDs between the writing of an empty memory cell and the overwriting of old memory content, because the latter must first be deleted before overwriting. The result of this is that the writing speed for SSDs can decrease rapidly as the filling level increases. Even still an SSD is superior to a hard disk with regard to performance.
Memory cards are used mainly as storage devices for phones and cameras
Graphics memory is memory dedicated to handling screen graphics output to a display device. It is normally located on a graphics card and is totally separate from the computer's main memory.