Meaning of memory in human analogy

 Human memory (brain) are play very important role in life. Brain, store all the information and human react the whole world with the help of these information’s. Now the same concept applies in the CPU. In computer worlds we can say that CPU work as a human and computer memory work as a brain. Like human work in daily life by the instruction of brain, same as CPU works instruction given by the memory. Therefore we can say that memory is a process by which information is encoded stored and retrieved.

 Computer Memory

In computing, memory refers to the physical devices used to store programs (sequence of instructions) or data (e.g. program information’s) on a temporary or permanent basis for use in a computer or other digital electronic devices. The term “memory” is often associated with addressable semiconductor memory, i.e. integrated circuits.

Need of Digital memory

Digital electronics deals with binary numbers. i.e. 0 & 1. So the basic goal of digital memory is to provide a means to store and access binary data which is sequence of 1’s and 0’. Memory is an important part of embedded systems. The cost and performance of an embedded systems heavily depends on the kind of memory devices it utilizes.

Memory are classify in three types

  1. RAM
    1. DRAM
    2. SRAM
  2. ROM
    1. PROM
    2. EPROM
  3. HYBIRD
    1. EEPROM
    2. FLASH

Need of RAM

In RAM, data is stored on a memory module to save and retrive data quickly. Whereas hard drives save and retrive data much slower than RAM. So speed is the main advanges of RAM.

RAM

RAM is acronym for Random Access Memory. It is a type of computer memory that can be accessed randomly, that is, any byte of memory can be accessed without touching the preceding bytes. RAM is associated with volatile types of memory, where it’s stored information is lost if the power is removed. RAM provided space for your computer to read and write daa to be accessed by the CPU, it is the “working memory” in the computer. RAM is usually referred to as computer’s memory.

Types of RAM

1. SRAM – Static RAM Retains its contents as long as electrical power is applied to the chip. If the power is turned off or lost temporarily, it’s content will be lost forever.

2. DRAM- Dynamic RAM It has an extremely short data lifetime typically about four milliseconds.

ROM

ROM is an acronym for read only memory. It is a class of storage medium used in computers and other electronic devices. It refers to computer memory chips containing permanent or semi-permanent data. Unlike RAM, ROM is non volatile, even after you turn off your computer, the contents of ROM will remain.  It is the computer memory on which data has been pre recorded. Once data has been written on to a ROM chip, it doesn’t be removed and can only be read. Almost every computer comes with a small amount of ROM containing the boot firmware. This consists of a few KB’s of code that tells the computer what to do when it start up e.g. running hardware diagnostics and loading the operating system into RAM. In a strict sense, ROM refers only to mask ROM, which is fabricated with the desired data permanently stored in it, and thus can never be modified. To update programs in ROM, you have to remove and physically replace your ROM chips.

Need Of ROM

ROM is important to the computers functionality because it retains all of the data even if computers is powered off. ROM is also used to store the data in order to even boot up a computers.

Types of ROM :- ROM store data permanently once data is written doesn’t change. But some time any application required to change data under certain circumstances then different types of ROM available in market. They are following types.

  1. Permanent group – ROM,PROM
  2. Semi permanent group – EPROM, EEPROM

PROM :- PROM is an acronym for programmable read only memory. PROM is a computer memory chip capable of being programmed after it has been created. Once the PROM has been programmed, the information written is permanent and doesn’t be change or delete. The process of writing data to the PROM involves a special piece of equipment called a device programmer. The device programmer writes data to device one word at a time by applying an electrical charge to input pins of the chip. PROM is a non-volatile memory that’s mean data remain when the power supply removed.

Need of PROM:- PROM’S are manufactured blank, and depending on the technology, can be programmed at final test or in system. The availability of this technology allows companies to keep a supply of blank PROM’S in stock, and program them at last minute to avoid large volume commitment.

EPROM:- EPROM is an acronym for erasable programmable read only memory. It is a type of memory chip that retains data when its power supply is switched off. In other words, it is non- volatile. Once programmed, an EPROM can be erased by exposing it to strong ultra violet light source. EPROM’S are easily recognizable by the transparent fused quartz window  in the top of the package through which the silicon chip is visible, and which permits exposure to ultra-voilet light during erasing. After erasing, this can be reprogrammed to write to an EPROM, a device called PROM programmer is used.

Need of EPROM:- They are widely used in personal computers because they enable the manufacturer to change the contents of PROM before the computer is actually shipped. This means that bugs can be removed and new versions can be installed shortly before delivery.

EEPROM:-  It is a type of hybrid memory. EEROM is an acronym for electrically erasable programmable read only memory. It is a type of no-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed. EEPROM is user-modifiable ROM that can be erased and reprogrammed repeatedly through the application of the higher than normal electrical voltage generated externally or internally in case of modern EEPROM’S. EEPPROM is similar to flash memory. The principal difference is that EEPROM required data to be written or erases one byte at a time whereas flash memory allows data to be written or erased in blocks. EEPROM’S have limited life that is, number of times it can be reprogrammed it limited.

Need of EEPROM:- EPROM usually must be removed from the device for erasing and programming, whereas EEPROM’S can be programmed and erased in circuit.