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As the name implies, a read-only memory(ROM) is a memory unit that performs the read operation only; it does not have a write capability. This implies that the binary information stored in a ROM is made permanent during the hardware production of the unit and cannot be altered by writing different words into it.

Whereas a RAM is a general-purpose device whose contents can be altered during the computational process, a ROM is restricted to reading words that are permanently stored within the unit. The binary information to be stored, specified by the designer, is then embedded in the unit to form the required interconnection pattern. ROMs come with special internal electronic fuses that can be programmed for a specific configuration. Once the pattern is established, it stays within the unit even when power is turned off and on again.

An m x n ROM is an array of binary cells organized into m words of n bits each. As shown in the block diagram below, a ROM has k address input lines to select one of words of memory, and n input lines, one for each bit of the word. An integrated circuit ROM may also have one or more enable inputs for expanding a number of packages into a ROM with larger capacity.

The ROM does not need a read-control line since at any given time, the output lines automatically provide the n bits of the word selected by the address value. Because the outputs are a function of only the present inputs (the address lines), a ROM is classified as a combinational circuit. In fact, a ROM is constructed internally with decoders and a set of OR gates. There is no need for providing storage capabilities as in RAM, since the values of the bits in the ROM are permanently fixed.

ROMs find a wide range of applications in the design of digital systems. As such, it can implement any combinational circuit with k inputs and n outputs. When employed in a computer system as a memory unit, the ROM is used for storing fixed programs that are not to be altered and for tables of constants that are not subject to change. ROM is also employed in the design of control units for digital computers. As such, they are used to store coded information that represents the sequence of internal control variables needed for enabling the various operations in the computer. A control unit that utilizes a ROM to store binary control information is called a microprogrammed control unit.

ROM: Different Types of ROM

The required paths in a ROM may be programmed in three different ways.

1. The first, mask programming, is done by the semiconductor company during the last fabrication process of the unit. This procedure is costly because the vendor charges the customer a special fee for custom masking the particular ROM. For this reason, mask programming is economical only if a large quantity of the same ROM configuration is to be ordered.

2. For small quantities it is more economical to use a second type of ROM called a Programmable Read Only Memory(PROM). The hardware procedure for programming ROMs or PROMs is irreversible, and once programmed, the fixed pattern is permanent and cannot be altered. Once a bit pattern has been established, the unit must be discarded if the bit pattern is to be changed.

3. A third type of ROM available is called Erasable PROM or EPROM. The EPROM can be restructured to the initial value even though its fuses have been blown previously. Certain PROMs can be erased with electrical signals instead of ultraviolet light. These PROMs are called Electrically Erasable PROM or EEPROM. Flash memory is a form of EEPROM in which a block of bytes can be erased in a very short duration.

Example applications of EEPROM devices are:

Storing current time and date in a machine.

Storing port statuses.

Example of Flash memory device applications are:

Storing messages in a mobile phone.

Storing photographs in a digital camera.

# data[].attributes.attachment_link.description
As the name implies, a read-only memory(ROM) is a memory unit that performs the read operation only; it does not have a write capability. This implies that the binary information stored in a ROM is made permanent during the hardware production of the unit and cannot be altered by writing different words into it.

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Random Access Memory, or RAM (pronounced as ramm), is the physical hardware inside a computer that temporarily stores data, serving as the computer's "working" memory.

Additional RAM allows a computer to work with more information at the same time, which usually has a considerable effect on total system performance.

Some popular manufacturers of RAM include Kingston, PNY, Crucial, and CORSAIR.

Put simply, the purpose of RAM is to provide quick read and write access to a storage device. Your computer uses RAM to load data because it's much quicker than running that same data directly off of a hard drive.

Think of RAM like an office desk. A desk is used for quick access to important documents, writing tools, and other items that you need right now. Without a desk, you'd keep everything stored in drawers and filing cabinets, meaning it would take much longer to do your everyday tasks since you would have to constantly reach into these storage compartments to get what you need, and then spend additional time putting them away.

Similarly, all the data you're actively using on your computer (or smartphone, tablet, etc.) is temporarily stored in RAM. This type of memory, like a desk in the analogy, provides much faster read/write times than using a hard drive. Most hard drives are considerably slower than RAM due to physical limitations like rotation speed.

RAM Works With Your Hard Drive (But They're Different Things)

RAM is typically referred to simply as "memory" even though other types of memory may exist inside a computer. RAM, which is the focus of this article, has nothing at all to do with the amount of file storage a hard drive has, even though the two are often incorrectly interchanged with each other in conversation. For example, 1 GB of memory (RAM) isn't the same thing as 1 GB of hard drive space.

Unlike a hard drive, which can be powered down and then back on without losing its data, the contents of RAM are always erased when the computer shuts down. This is why none of your programs or files are still open when you turn your computer back on.

Each motherboard supports only a certain range of memory types in certain combinations, so always check with your motherboard manufacturer before making a purchase.

The RAM in Your Computer Resembles a Ruler or 'Stick'

A standard module or stick of desktop memory is a long, thin piece of hardware that resembles a short ruler. The bottom of the memory module has one or more notches to guide for proper installation and is lined with numerous, usually gold-plated, connectors.

Memory is installed in memory module slots located on the motherboard. These slots are easy to find- just look for the small hinges that lock the RAM in place, located on either side of the similarly-sized slot on the motherboard.

Memory modules come in various capacities and variations. Modern memory modules can be purchased in 256 MB, 512 MB, 1 GB, 2 GB, 4 GB, 8 GB, and 16+ GB sizes. Some examples of the different types of memory modules include DIMM, RIMM, SIMM, SO-DIMM, and SO-RIMM.

How Much RAM Do You Need?

Just like with a CPU and hard drive, the amount of memory you need for your computer depends entirely on what you use, or plan to use, your computer for.

For example, if you're buying a computer for heavy gaming, then you'll want enough RAM to support smooth gameplay. Having just 2 GB of RAM available for a game that recommends at least 4 GB is going to result in very slow performance if not total inability to play it (especially if the recommendation is 8 GB or more).

On the other end of the spectrum, if you use your computer for light internet browsing and no video streaming, games, memory-intensive applications, etc., you could easily get away with less memory.

The same goes for video editing applications, programs that are heavy on 3D graphics, etc. You can normally find out before you buy a computer just how much RAM a specific program or game requires, often listed in a "system requirements" area of the website or product box.

It would be hard to find a new desktop, laptop, or even tablet that comes with less than 2 to 4 GB of RAM pre-installed. Unless you have a specific purpose for your computer apart from regular video streaming, internet browsing, and normal application use, you probably don't need to buy a computer that has any more RAM than that.

Troubleshooting RAM Issues

The first thing you should do if you suspect an issue with one or more RAM sticks is to reseat the memory modules. If one of the RAM sticks hasn't been securely inserted into its slot on the motherboard, it's possible that even a small bump could knock it out of place and cause memory problems that you didn't have before.

If reseating the memory doesn't improve the symptoms, we recommend using one of these free memory test programs. Since they work from outside the operating system, they work with any kind of PC-Windows, Mac, Linux, etc.

Your best option is to replace the memory in your computer if one of those tools identifies a problem, no matter how small.

Advanced Information on RAM

Though RAM is explained as a volatile memory in the context of this website (with regard to internal computer memory), it also exists in a non-volatile, non-alterable form called read-only memory (ROM). Flash drives and solid state drives, for example, are variants of ROM that retain their data even without power, but can be altered.

There are many types of RAM, but the two main ones are static RAM (SRAM) and dynamic RAM (DRAM). Both are volatile. SRAM is faster but more expensive to produce than DRAM, which is why the latter is more prevalent in today's devices. However, SRAM is sometimes seen in small doses in various internal computer parts, like with the CPU and as hard drive cache memory.

Some software, like SoftPerfect RAM Disk, can create what's called a RAM disk, which is essentially a hard drive that exists inside RAM. Data can be saved to, and opened from, this new disk as if it were any other, but read/write times are much quicker than using a regular hard disk because RAM is much faster.

Some operating systems can utilize what's called virtual memory, which is the opposite of a RAM disk. This is a feature that sets aside hard disk space for use as RAM. While doing so can increase the overall available memory for applications and other uses, it may negatively affect system performance due to the fact that hard drives are slower than RAM sticks.

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# data[].attributes.attachment_link.description
Random Access Memory, or RAM (pronounced as ramm), is the physical hardware inside a computer that temporarily stores data, serving as the computer's "working" memory. Additional RAM allows a computer to work with more information at the same time, which usually has a considerable effect on total system performance.

# data[].attributes.body
1. Read only memory.
2. Rom is also a form of data storage that generally Store hardwired instructions for the computer to start initially.
3. Rom cannot be easily altered or reprogrammed.
4. Rom stores the program required to initially boot the computer or reboot the computer.
5. It only allows reading.

# data[].attributes.body
1. Random access memory.
2. Ram is a form of data storage that can be accessed randomly at any time in any order.
3. Ram content can be changed or altered as and when required.
4. Ram allows the computer to read data quickly to run application.
5. It allows reading and writing.