What is Memory ? Types of Memory
Two Types of Memory
1--Primary Memory
2--Secondary Memory
1--Primary Memory--
Primary memory is computer memory that a processor or computer accesses first or directly. It allows a processor to access running execution applications and services that are temporarily stored in a specific memory location.
Definition 2: In the enterprise, primary storage holds data that is in active use.
Primary memory is also known as primary storage or main memory.
2--Secondary Memory-- Secondary memory is computer memory that is non-volatile and persistent in nature and is not directly accessed by a computer/processor. It allows a user to store data that may be instantly and easily retrieved, transported and used by applications and services.
2--Secondary storage : sometimes called auxiliary or external storage, is non-volatile storage that is not under the direct control of a computer’s central processing unit (CPU) or does not directly interact with an application.
Secondary memory is also known as secondary storage.
Types of Primary Memory
(1) ROM :Read only memory-- In this type of memory the information is stored permanently, its is not lost after the system shuts down. The advantage of using this memory is that there are some complex functions like translators that are used repeatedly . These functions are permanently stored in the ROM and these instructions are hard wired in ROM so the execution is very fast.
There are different types of ROM . They are described below
Types of ROM
In a strict ROM the device is constructed with the program already inside. But PROM is produced blank. It is programmed only later. The advantage of using PROM is that a company can change the program it is going to store when ever they want with out loss of hardware.
Erasable programmable ROM(EPROM): This type of PROM can be erased and reprogrammed a number of times. Here the chip that holds the memory is exposed through a glass widow. A strong UV light of a particular frequency if shined through this glass window will erase the EPROM
Electrically erasable programmable ROM(EPROM): This PROM can be reprogrammed under software control.
(2)RAM:Random Access Memory--
Unlike the ROM this is type of memory is volatile and can erased every now and then. Data can be written to it and may be retrieved from it according to the address given. There are two types of RAM dynamic RAM and Static RAM.
RAM Example-- calculator
Static RAM: Retains its content as long as the power supply is there. Once the power supply is lost it looses its contents.
Dynamic RAM: Cannot retain the data even if constant power supply is there. The life time of data in it is milliseconds.
DRAM controller is used to refresh the data in Dynamic RAM before it starts to fade. So with DRAM controller we can make Dynamic RAM function just like Static RAM.
SDRAM (synchronous DRAM)
SDRAM (synchronous DRAM) is a generic name for various kinds of dynamic random access memory (DRAM) that are synchronized with the clock speed that the microprocessor is optimized for. This tends to increase the number of instructions that the processor can perform in a given time. The speed of SDRAM is rated in MHz rather than in nanoseconds (ns). This makes it easier to compare the bus speed and the RAM chip speed. You can convert the RAM clock speed to nanoseconds by dividing the chip speed into 1 billion ns (which is one second). For example, an 83 MHz RAM would be equivalent to 12 ns.
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