Difference Between RAM and ROM

Difference Between RAM and ROM

RAM is Random Access Memory.

ROM is Read Only Memory.






RAM is the memory available for the operating system, programs and processes to use when the computer is running.


ROM is the memory that comes with your computer that is pre-written to hold the instructions for booting-up the computer.






RAM requires a flow of electricity to retain data (e.g. the computer powered on).


ROM will retain data without the flow of electricity (e.g. when computer is powered off).






RAM is a type of volatile memory. Data in RAM is not permanently written. When you power off your computer the data stored in RAM is deleted.


ROM is a type of non- volatile memory. Data in RAM is permanently written and is not erased when you power off your computer.






There are different types of RAM, including DRAM (Dynamic Random Access Memory) and SRAM (Static Random Access Memory).


There are different types of ROM, including PROM (programmable read-only memory) that is manufactured as blank memory (e.g. a CD-ROM) and EPROM (erasable programmable read-only memory).






There are many differences between RAM and ROM memory but there are also a couple similarities (and these are very easy to remember). Both types of memory used by a computer, and they are both required for your computer to operate properly and efficiently.






Have more questions about RAM and ROM? Feel free to ask in the comments section!

ROM

Read-only memory (ROM), also known as firmware, is an integrated circuit programmed with specific data when it is manufactured. ROM chips are used not only in computers, but in most other electronic items as well. ­ ­







­In this article, you will learn about the different types of ROM and how each works. This article is one in a series of articles dealing with computer memory, including:

Function of RAM

RAM

Random access memory (RAM) is the best known form of computer memory. RAM is considered "random access" because you can access any memory cell directly if you know the row and column that intersect at that cell.








The opposite of RAM is serial access memory (SAM). SAM stores data as a series of memory cells that can only be accessed sequentially (like a cassette tape). If the data is not in the current location, each memory cell is checked until the needed data is found. SAM works very well for memory buffers, where the data is normally stored in the order in which it will be used (a good example is the texture buffer memory on a video card). RAM data, on the other hand, can be accessed in any order.






Similar to a microprocessor, a memory chip is an integrated circuit (IC) made of millions of transistors and capacitors. In the most common form of computer memory, dynamic random access memory (DRAM), a transistor and a capacitor are paired to create a memory cell, which represents a single bit of data. The capacitor holds the bit of information -- a 0 or a 1 (see How Bits and Bytes Work for information on bits). The transistor acts as a switch that lets the control circuitry on the memory chip read the capacitor or change its state.






­A capacitor is like a small bucket­ that is able to store electrons. To store a 1 in the memory cell, the bucket is filled with electrons. To store a 0, it is emptied. The problem with the capacitor's bucket is that it has a leak. In a matter of a few milliseconds a full bucket becomes empty. Therefore, for dynamic memory to work, either the CPU or the memory controller has to come along and recharge all of the capacitors holding a 1 before they discharge. To do this, the mem­ory controller reads the memory and then writes it right back. This refresh operation happens automatically thousands of times per second.­

The capacitor in a dynamic RAM memory cell is like a leaky bucket. It needs to be refreshed periodically or it will discharge to 0. This refresh operation is where dynamic RAM gets its name. Dynamic RAM has to be dynamically refreshed all of the time or it forgets what it is holding. The downside of all of this refreshing is that it takes time and slows down the memory.






In this article, you'll learn all about what RAM is, what kind you should buy and how to install it. See the next page to learn more about dynamic RAM and memory cells.­

Computer Memory Basics

Computer Memory Basics

Although memory is technically any form of electronic storage, it is used most often to identify fast, temporary forms of storage. If your computer's CPU had to constantly access the hard drive to retrieve every piece of data it needs, it would operate very slowly. When the information is kept in memory, the CPU can access it much more quickly. Most forms of memory are intended to store data temporarily.






As you can see in the diagram above, the CPU accesses memory according to a distinct hierarchy. Whether it comes from permanent storage (the hard drive) or input (the keyboard), most data goes in random access memory (RAM) first. The CPU then stores pieces of data it will need to access, often in a cache, and maintains certain special instructions in the register. We'll talk about cache and registers later.






All of the components in your computer, such as the CPU, the hard drive and the operating system, work together as a team, and memory is one of the most essential parts of this team. From the moment you turn your computer on until the time you shut it down, your CPU is constantly using memory. Let's take a look at a typical scenario:






You turn the computer on.


The computer loads data from read-only memory (ROM) and performs a power-on self-test (POST) to make sure all the major components are functioning properly. As part of this test, the memory controller checks all of the memory addresses with a quick read/write operation to ensure that there are no errors in the memory chips. Read/write means that data is written to a bit and then read from that bit.


The computer loads the basic input/output system (BIOS) from ROM. The BIOS provides the most basic information about storage devices, boot sequence, security, Plug and Play (auto device recognition) capability and a few other items.


The computer loads the operating system (OS) from the hard drive into the system's RAM. Generally, the critical parts of the operating system are maintained in RAM as long as the computer is on. This allows the CPU to have immediate access to the operating system, which enhances the performance and functionality of the overall system.


When you open an application, it is loaded into RAM. To conserve RAM usage, many applications load only the essential parts of the program initially and then load other pieces as needed.


After an application is loaded, any files that are opened for use in that application are loaded into RAM.


When you save a file and close the application, the file is written to the specified storage device, and then it and the application are purged from RAM.


­In the list above, every time something is loaded or opened, it is placed into RAM. This simply means that it has been put in the computer's temporary storage area so that the CPU can access that information more easily. The CPU requests the data it needs from RAM, processes it and writes new data back to RAM in a continuous cycle. In most computers, this shuffling of data between the CPU and RAM happens millions of times every second. When an application is closed, it and any accompanying files are usually purged (deleted) from RAM to make room for new data. If the changed files are not saved to a permanent storage device before being purged, they are lost.






One common question about desktop computers that comes up all the time is, "Why does a computer need so many memory systems?"