memory and storage Flashcards
primary storage
it refers to the memory areas that the CPU can access very quickly, like CPU registers, RAM, ROM and cache. primary storage has the fastest read / write speed
RAM
RAM, often referred to as primary memory is high speed read / write memory that is volatile meaning that all data and instructions are removed when the power is turned off. when a computer boots up, the OS is copied from the secondary to the RAM. when the RAM is used up, the unused applications are offloaded to the Virtual memory
2 types of RAM
Static RAM - use transistors to store data
dynamic RAM - use capacitors to store data
ROM
it comes on a small, factory made chip built into the motherboard and is read only. it contains all the instructions a computer needs to properly operate. these include the BIOS, POST and the bootstrap. As soon as the computer powers on, the CPU reads the instructions from the ROM. This tells the CPU to perform self checks and set up the computer, e.g. Test the memory is working, see what hardware is present and copy the OS from the secondary storage into the RAM.
It controls basic technical configurations of the computer such as the processor speed and system time.
bootstrap
the first piece of code that runs when a machine starts
POST
power on self test - is the initial set of diagnostic tests performed by the computer right after it turns on
BIOS
basic input output system - it is software stored on a small memory chip on the motherboard
virtual memory
Virtual memory is a reserved/allocated area of disk used as an extension of RAM.
When RAM becomes full of programs and/or data, instructions /data not currently being used, these are swapped to virtual memory.
This frees area in RAM for new programs or data.
When the old instructions/data are needed, something else is swapped out and the needed instructions/data swapped back into RAM.
advantages of SWAP memory
uses cheap secondary storage on the hard drive, prevents error messages saying “out of memory” and files will stay open
disadvantages of SWAP memory
accessing virtual memory is very slow, the existing data is the RAM needs to be copied to the virtual memory, then the data in virtual memory needs to be copied to the RAM
secondary storage
Secondary storage is required for permanent storage of software and data / it is non-volatile
it is where all data (OS, applications and user files) are stored when not in use. it includes magnetic HDDs, SSDs, digital versatile discs (DVDs), compact disc (CD), SD cards and USB drives. it is non - volatile and read / write speeds are much slower compared to primary storage
magnetic storage
Magnetic devices such as hard disk drives use magnetic fields to magnetise tiny individual sections of a metal spinning disk. Each tiny section represents one bit. A magnetised section represents a binary ‘1’ and a demagnetised section represents a binary ‘0’. These sections are so tiny that disks can contain terabytes (TB) of data.
advantages of magnetic storage
capacity - high storage
cost - low per gigabyte
speed - moderate read / write access
disadvantages of magnetic storage
durability - moving parts can get damaged if dropped
portability - heavy and bulky making them less convenient for transport
reliability - prone to mechanical failure (moving parts)
noise - loud (spinning discs)
optical storage
Optical devices use a laser to scan the surface of a spinning disc made from metal and plastic. The disc surface is divided into tracks, with each track containing many flat areas and hollows. The flat areas are known as lands and the hollows as pits.
When the laser shines on the disc surface, lands reflect the light back, whereas pits scatter the laser beam. A sensor looks for the reflected light. Reflected light (lands) represents a binary 1, and no reflection (pits) represents a binary 0.
