Memory and storage Flashcards
Primary storage
Primary storage refers to the memory areas that the CPU can access very quickly. They are volatile with the exception of ROM. They have much faster access speeds than secondary storage. Due to the higher performance primary storage costs more per GB than secondary storage.
Random access memory (RAM)
RAM (Random Access Memory) is primary storage that is directly connected to the CPU and holds the data and instructions that are currently in use.
RAM is volatile which means the contents of RAM are lost when the power is turned off.
For the CPU to access the data and instructions they must be copied from secondary storage.
RAM is very fast working memory, much faster than secondary storage.
RAM is read/write which means data can be read from and written to.
In comparison to ROM, it has a much larger capacity.
Static RAM - use transistors to store data.
Dynamic RAM - use capacitors to store data.
Read only memory (ROM)
ROM (Read Only Memory) is primary storage that holds the first instructions a computer needs to start up (Bootstrap).
ROM contains the BIOS (Basic Input Output System).
ROM is a small memory chip located on the computers motherboard.
ROM is fast memory, much faster than secondary storage but slower than RAM
ROM is non-volatile which means the contents of ROM are not lost when the power is turned off.
ROM is read only which means data can only be read from.
In comparison to RAM, it has a much smaller capacity.
Virtual memory
Virtual memory is an extension of primary storage (RAM) located on secondary storage.
In situations where RAM is close to being full, virtual memory can be used so that the computer remains operational.
Programs and data not currently being executed are transferred to virtual memory.
Programs and data are transferred back to RAM when they are needed.
Virtual memory is much slower than RAM and it’s use will impact negatively on system performance.
To avoid the use of virtual memory, increase the size of the RAM.
Secondary storage
A computer needs secondary storage for long term storage of programs and data that are currently not in use .
Secondary storage is needed as ROM is read only and RAM is volatile.
Secondary storage holds the programs and data whilst the computer is turned off (non-volatile).
Performance of secondary storage is slower than primary storage but capacity is much higher which makes it perfect for backup & archive of data files.
Advantages and disadvantages of Magnetic storage
Advantages -
capacity - high storage
cost - low per gigabyte
speed - moderate read / write access
Disadvantages -
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)
Advantages and disadvantages of optical storage
Advantages -
cost - low per gigabyte
durability - no moving parts
portability - small and no moving parts
noise - silent
Disadvantages -
capacity - very low
speed - very slow read / write speed
reliability - prone to scratches
Advantages and disadvantages of Solid state storage
Advantages -
capacity - medium / high storage
speed - very fast read / write access
durability - no moving parts
portability - small and no moving parts
noise - silent
Disadvantages -
cost - very high per gigabyte
reliability - limited read / write cycles
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.
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.
solid state storage
Solid state storage is a type of non volatile media that uses electronic circuits to store 0s and 1s. Most SSDs use a type of flash memory. They have no moving parts and are used for the same purpose as HDDs for internal / external storage.
BIOS
basic input output system - it is software stored on a small memory chip on the motherboard
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
