23-05-2012, 05:26 PM
Basic structure of computer
Basic structure of computer.ppt (Size: 262.5 KB / Downloads: 35)
Primary memory
– Connected to processor through memory bus
– Relatively fast access
– Typically volatile (lost on power-off)
Secondary memory
– Typically external memory such as hard drives
– VERY slow access
– Very cheap
Primary Memory
Primary memory is the memory that can be directly accessed by the CPU which constantly interacts with it, retrieves data stored therein, goes through instructions and execute them as per the requirement.
RAM
RAM is an acronym for Random Access Memory that is also known as volatile memory, because the data it holds is lost when the desktop PC or laptop/notebook computer using it is switched off. Briefly, RAM memory is used by the system to store data in the form of files for processing by a computer's central processing unit (CPU), also known as the processor.
The random access memory comprises hundreds of thousands of small capacitors that store loads. When loaded, the logical state of the capacitor is equal to 1, otherwise it is 0, meaning that each capacitor represents one memory bit.
Categorizing Storage Devices
Storage devices hold data, even when the computer is turned off.
The physical material that actually holds data is called a storage medium. The surface of a floppy disk is a storage medium.
The hardware that writes data to or reads data from a storage medium is called a storage device. A floppy disk drive is a storage device.
SRAM
Static RAM (SRAM) stores binary bits in such a manner that the bits remain in RAM as long as power to the chip is not interrupted
it doesnot need to be refreshed periodically.
It is often used as cache memory.
DRAM
Dynamic RAM (DRAM), on the other hand, requires that stored data be refreshed, or rewritten, periodically to keep it from fading away. As a matter of fact, each bit in the DRAM must be refreshed at least once every 2 milliseconds or the data dissipates.
This is done by placing the memory on a refresh circuit that rewrites the data several hundred times per second.
ROM
ROM: A regular ROM is constructed from hard-wired logic, encoded in the silicon itself, much the way that a processor is.
It is designed to perform a specific function and cannot be changed.
This is inflexible and so regular ROMs are only used generally for programs that are static (not changing often) and mass-produced.
These are used to write micro codes and often known as mask programmable.