1.2.1 Primary Storage (Memory) Flashcards
What does primary storage consist of?
RAM
ROM
What does primary storage do?
Holds data and instructions which the CPU needs access to while a computers running.
Characteristics of primary storage
-Very quick because it is directly accessed by CPU as it is physically closer to CPU
-Typically smaller in storage size
Why do computers need primary storage?
Program instructions and data must be copied from the hard drive into RAM to be processed by the CPU because primary storage access speeds are much faster than secondary storage devices such as the hard drive.
Advantage of primary storage for CPU?
The CPU can much more quickly access data form primary storage than secondary storage. This is why computers have primary storage.
RAM
Holds the operating system, programs and data in use by the CPU while the computer is running.
Characteristics of RAM
-Volatile
-Read and Write
-Large in comparison to ROM
ROM
-Holds the first instructions for when a computer is first turned on (known as bootstrap).
-Programs may be stored in ROM in embedded systems.
Characteristics of ROM
-Non-volatile
-Read only
-Small in comparison to RAM
Volatile
Volatile memory is temporary - data is lost whenever the power is turned off.
Non-volatile
Non-volatile memory is permanent - it keeps its contents even when it has no power.
Virtual memory
Area of secondary storage sed by OS as extra RAM
Why is volatile memory needed?
When there is not enough physical RAM to store the open programs.
How does virtual memory work?
-Programs are transferred out to VM from RAM when they are not currently being executed (when RAM = full)…
-…and when these programs are needed again, they are transferred back to RAM form VM.
What are the disadvantages of virtual memory?
It can make a computer slow to respond when switching between applications or when using a memory-intensive application (due to data constantly moving between VM and RAM just to keep the program running).
Where is virtual memory found?
It is held on the hard disk
Data transfer rates are much _________ on secondary storage than RAM
slower
Cache
Very fast memory in the CPU. Slower than the registers but faster than RAM.
What does cache store?
Regularly used data so that the CPU can access it quickly the next time it is needed.
Where does the CPU check first when it requests data?
Checks the cache first to see if data is there, but if not, it will fetch it from RAM.
