What is RAM & ROM

Computer Fundamental / By / / 4 minutes of reading

Semi Conductor memories

This type of storage devices are based on the principles of storage chips. These are very thin silicon chips, consisting of number of small storage cells that can hold data. These units are constructed as integrated circuits, meaning that number of transistors are integrated or combined together on a thin silicon wafer. Faster and more expensive bipolar semi conductor chips are often used in ALU and high speed buffer storage sections of CPU. Slower and less expensive chips that employ metal-oxide semi-conductor (MOS) technology are used in main memory section.

These are again divided into – permanent (Non Volatile) & non permanent (Volatile). Non volatile chips can retain the data permanently i.e. they hold data even when the computer is switched off. (E.g.- ROM BIOS) On the other hand Volatile chips lose their contents when the computer’s power is switched off i.e. these chips provide volatile storage. RAM is the best example for this type of memory.

What is RAM

The memory system constructed with metal oxide semi conductor storage elements that can be changed is called Random Access Memory. It is used to hold intermediary data in the computer. The contents of this memory chips are temporary and can be easily changed. It is the work space for the computer’s processor. When people talk about computer memory, they usually mean volatile memory.

Why is it called so?

It is called random access memory because access time in RAM is independent of the address of the data. Each storage location (address) inside the memory is as easy to reach as any other location and takes the same amount of time. One can reach into the memory at random and insert or remove numbers in any location at anytime.

Types of RAM:

  1. Dynamic RAM: It is the most common type of main memory. It is dynamic because each memory cell quickly loses its charge. So it must be refreshed for hundreds of times each second. In olden days refreshing was done by Microprocessor. Due to this, lot of processing power was wasted. But today’s dynamic RAM is coming with built in refresh circuits. This saves lot of processing power.
  2. Static RAM: Static RAM (SRAM) is like DRAM but it is faster, larger and more expensive. It is static because it is not required to refresh the contents of RAM continuously. Because of its speed, SRAM is mainly used in special area of memory called cache memory.
  3. Static RAM Vs Dynamic RAM: Static RAM can retain the stored data as long as power remains in. Whereas in dynamic RAM, the stored information disappears after every few milliseconds. Therefore, data must be refreshed before it disappears. The power consumption of dynamic RAM is less than that of static RAM.

What is ROM?

Another type of computer memory is Read-Only-Memory (ROM). It is used for storing micro programs, not available to normal programmers. The information is permanently stored during manufacturing. The information from the memory can be read but fresh information cannot be written. Generally ROM is used to store instructions that are frequently needed, for executing small, extremely basic operations, which will not be available in the computer’s circuitry. For e.g. ROM may be used for code converter, function generator (e.g. sine, cosine, tangent etc.) and character generators (e.g. characters displayed in dot matrix form).

Different kinds of ROM:

  1. PROM: Programmable Read Only Memory is a non-volatile memory which allows the user to program the chip with a PROM writer. User can record any data or instructions. The only problem with PROM chips is that once data is recorded on them, it cannot be changed.
  2. EPROM: EPROM stands for Erasable Programmable Read Only Memory. EPROM chips can be electrically programmed. Unlike ROM and PROM chips, EPROM chips can be erased and reprogrammed. With the help of ultraviolet light, the data or instructions on an EPROM chip can be erased and new data can be recorded in its place.
  3. EEPROM: It stands for Electrically Erasable Programmable Read Only Memory. This is the latest addition to the ROM family of chips. For the purpose of reprogramming, they need not be removed from the machine. Changes can be made electrically, under the control of a software.

 

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