ROM Works

From How ROM Works

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Read-only memory is essential to your computer. You'll also find ROM in video games, cell phones and microwaves. Learn about the different types.. Similar to RAM, ROM chips (Figure 1) contain a grid of columns and rows. But where the columns and rows intersect, ROM chips are fundamentally...

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ROM Types
From How ROM Works

Read-only memory is essential to your computer. You'll also find ROM in video games, cell phones and microwaves. Learn about the different types.. There are five basic ROM types: ROM PROM EPROM EEPROM Flash memory Each type has unique characteristics, which you'll learn about in this article...

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Introduction to How ROM Works

Read-only memory is essential to your computer. You'll also find ROM in video games, cell phones and microwaves. Learn about the different types.. Computer Memory Image Gallery2008 HowStuffWorksROM is used in most electronic devices. See more computer memory pictures.Read-only memory (ROM...

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PROM
From How ROM Works

Read-only memory is essential to your computer. You'll also find ROM in video games, cell phones and microwaves. Learn about the different types.. Creating ROM chips totally from scratch is time-consuming and very expensive in small quantities. For this reason, mainly, developers created a type...

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EEPROMs and Flash Memory
From How ROM Works

Read-only memory is essential to your computer. You'll also find ROM in video games, cell phones and microwaves. Learn about the different types.. byte at a time. See How Flash Memory Works to learn more about this type of ROM and its applications. For more information on ROM and other types...

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EPROM
From How ROM Works

Read-only memory is essential to your computer. You'll also find ROM in video games, cell phones and microwaves. Learn about the different types.. Working with ROMs and PROMs can be a wasteful business. Even though they are inexpensive per chip, the cost can add up over time. Erasable...

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Installing the Hard Drive
From How to Build a Computer

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The hard drive sits in a bracket and is connected directly to the power supply. Find out how to install a hard drive and learn where the CD-ROM drive.. The last steps are installing the hard drive and the CD-ROM drive. The case has a removable bracket with four rubber grommets on it, which line...

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Microprocessor Instructions
From How Microprocessors Work

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that RAM starts at address 128 in this processor, and ROM (which contains the assembly language program) starts at address 0, then for our simple...

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Why can I play some DVD movies, but not others, on my computer DVD-ROM?

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Why can I play some DVD movies, but not others, on my computer DVD-ROM?.. player or DVD-ROM drive sold in the country where the DVD movie was sold. The actual region code is in one byte on the DVD (digital versatile disc...

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* > CD/DVD Drives & Burners

Microprocessor Memory
From How Microprocessors Work

Microprocessor memory helps with the microprocessor's basic functions. Learn about microprocessor memory, ROM, BIOS and what the boot sector is...The previous section talked about the address and data buses, as well as the RD and WR lines. These buses and lines connect either to RAM or ROM...

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RAM WORKING

From How RAM Works

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Types of RAM have changed tremendously over time. Learn about the types of RAM and what kind of RAM your computer needs... The following are some common types of RAM: SRAM: Static random access memory uses multiple transistors, typically four to six, for each memory...

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How to Install RAM
From How RAM Works

A RAM upgrade can greatly extend your computer's lifespan. Learn how to install RAM and find the best prices on RAM upgrades...Most of the time, installing RAM is a very simple and straightforward procedure. The key is to do your research. Here's what you need to know...

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Static RAM
From How RAM Works

Static RAM offers premium performance at a premium price. Learn about static RAM and memory modules and printed circuit boards... Static RAM uses a completely different technology. In static RAM, a form of flip-flop holds each bit of memory (see How Boolean Logic Works...

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RAM Quiz

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With the RAM Quiz on HowStuffWorks, see how much you know about this type of computer memory. Explore RAM technology and applications with the RAM..You've probably heard about RAM memory when people talk about computers -- how much RAM a desktop might need, whether or not someone is adding more...

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Introduction to How RAM Works

RAM is the best known form of computer memory and easy to upgrade. Learn how RAM works, what kind of RAM to buy, and how to install it... Computer Hardware Image GalleryRAM is the best known form of computer memory and easy to upgrade. See more computer hardware pictures.Random access...

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How Much RAM Do You Need?
From How RAM Works

How much RAM is enough? Find out much RAM you need for any task, learn about the types of RAM and find the best prices for RAM upgrades...It's been said that you can never have enough money, and the same holds true for RAM, especially if you do a lot of graphics-intensive work...

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Memory Cells and DRAM
From How RAM Works

that include identifying the type, speed and amount of memory and checking for errors.Static RAM works differently from DRAM. We'll look at how in the next...

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Memory Modules
From How RAM Works

The type of board and connector used for RAM in desktop computers has evolved over the past few years. The first types were proprietary, meaning...

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Choosing RAM
From How to Add RAM to Your Laptop

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When choosing RAM for your laptop, you should take into account a few factors. Get advice for choosing RAM for your laptop... � iStockphoto.com/ilmwa555Everyone has their own needs for their laptop, so what should you look for when buying RAM?When most people refer to a...

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Adding RAM
From How to Add RAM to Your Laptop

Adding RAM to your laptop isn't as hard as you might think. See these tips and instructions for adding RAM to your laptop... Once you've purchased the necessary RAM module, you're ready to add more memory to your computer. Before you start anything, make sure the laptop...

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Memory hierarchy of RAM

Many computer systems have a memory hierarchy consisting of CPU registers, on-die SRAM caches, external caches, DRAM, paging systems, and virtual memory or swap space on a hard drive. This entire pool of memory may be referred to as "RAM" by many developers, even though the various subsystems can have very different access times, violating the original concept behind the random access term in RAM. Even within a hierarchy level such as DRAM, the specific row, column, bank, rank, channel, or interleave organization of the components make the access time variable, although not to the extent that rotating storage media or a tape is variable. The overall goal of using a memory hierarchy is to obtain the higher possible average access performance while minimizing the total cost of entire memory system. (Generally, the memory hierarchy follows the access time with the fast CPU registers at the top and the slow hard drive at the bottom.)

In many modern personal computers, the RAM comes in an easily upgraded form of modules called memory modules or DRAM modules about the size of a few sticks of chewing gum. These can quickly be replaced should they become damaged or too small for current purposes. As suggested above, smaller amounts of RAM (mostly SRAM) are also integrated in the CPU and other ICs on the motherboard, as well as in hard-drives, CD-ROMs, and several other parts of the computer system.

Did You Know . . . ?

# Social Media: Tips for Small Business Marketing

The Internet

* Social Media: Tips for Small Business Marketing

* Traceroute and Ping: What's the Difference?

* The Difference Between a Virus, Worm and Trojan Horse

* SSL Basics and Beyond

* Ad Network Primer: Tips for Targeted Campaigns

* Five SEO Tips for Driving Search Engine Traffic

* The Difference Between LinkedIn and Facebook

* Antivirus and Antispyware Software: What's The Difference?

* Laptops and Notebooks — What's the Difference?

* The Difference Between VoIP and PSTN Systems

* All About Online Forums

* How to Deal With Pop-Ups

* What Do Temporary Internet Files Do?

* 8 Terms to Watch in 2008

* What Is The Semantic Web?

* What Is a Widget

* Understanding and Resolving IP Address Conflicts

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* All About Cookies and You

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* Understanding Internet Governance

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* The Birth of the Internet

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Hardware/Software

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Computer Science

* The Difference Between Laptop and Desktop Memory

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* Different Types of Memory Cards

* Understanding LAMP and Its Effect on Web Development

* Metadata: Data About Data

* Storage Virtualization: Myths, Realities and Other Considerations

* The Differences Between WEP and WPA

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* Understanding Hardware-Assisted Virtualization

* How to Completely Erase a Hard Disk Drive

* Ten Terms to Watch in 2007

* Understanding IPv6

* All About Network Access Controls

* Understanding NAT and PAT

* iSCSI vs. Fibre Channel

* Understanding Rootkits

* The Benefits of Tiered Storage

* Understanding OSPF Routing

* What is a Virtual Tape Library

* Understanding Routers

* What Is Perpendicular Hard Drive Technology?

* Understanding TCP, the Protocol

* Top 10 Terms to Know for the New Year

* In the OSI Model — Understanding the Data Layer

* The OSI Reference Model — Understanding Layers

* How Biometrics Security Works

* What's the Best Network Operating System?

* The Many Flavors of OFDMA

* How Surround Sound Works

* All About Digital TV — DTV and HDTV

* Deciphering the Latest Wireless Acronyms

* Understanding Web Services

* Digital Audio Formats

* What Is CPU Overclocking?

* What Is USB?

* Pardon the Intrusion: All About IPS & IDS

* All About PDF Technology

* Tech Terms That Are Strange but True

* All About RFID

* What Is 64-bit Computing?

* How Fingerprint Scanners Work

* Is It Possible to Eavesdrop on Electromagnetic Radiation?

* The Science of Color

* Static Electricity and Computers

CATEGORIES

Communications

* Application Service Providers (ASPs)
* Business Computing
* Business Tools
* Communications Software
* Communications Standards
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* Data Transfer Rates
* Digital Rights Management
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* Ethics
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Computer Industry Companies

* Hardware Companies
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Computer Science

* Artificial Intelligence
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* Virtualization
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Data

* Data Compression
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* Data Sizes
* Data Structures
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* Encryption
* Error Correction
* Special Characters

Graphics

* 3-D Graphics
* Animation
* Business Presentation
* Digital Cameras
* Digital Photography
* Color
* Graphics Software
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Hardware

* Adapters/Cards
* Addressing
* Buses
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* Data Storage
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* Keyboards
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Mobile Computing

* Flat-Panel displays
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Multimedia

* Animation
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Networks

* Data Transfer Rates
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Open Source (OSRC)

* OSRC Databases
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Operating Systems

* DOS
* File Management
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* User Interfaces
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Programming

* Addressing
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* Compiling, Binding and Linking
* Data Structures
* Expressions
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* Operators and Operations
* Procedures, Functions and Routines
* Programming Languages
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* Vocations
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Software

* Applications
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* Graphics Software
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* User Interfaces
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Standards

* Communications Standards
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* Display Standards
* Formatting Standards
* Graphics Standards
* Miscellaneous Standards
* Network Protocols
* Networking Standards
* Standards Organizations
* Video Formats

Types of Computers

* Macintosh
* Notebook Computers
* PCs
* Servers
* Supercomputers
* Workstations

World Wide Web

* Browsers
* HTML
* Markup Languages
* Search Engines
* Social Media
* Web Development

How many processors do you need for a Snipe Hunt?

Posted by Cameron Hughes, Tracey Hughes 11:53 PM | February 16, 2009

Snipe hunts, fool's gold, solutions to AI-complete problems, I've been victimized by them all. Although I have gotten over the snipe hunts and fool's gold, I haven't been able to quite shake the AI-complete part yet. Why can't I just throw more processors at the problem? Why can't the fastest beat the hardest? Oops, let me regress for a moment. I said I would have to stir up what I meant by AI-complete, so first let me do so

Security Reminder, or Who's That Looking Over Your Shoulder?

Security Reminder, or Who's That Looking Over Your Shoulder?
Posted by Jon Erickson 05:56 PM | February 25, 2009

It doesn't matter which coffee shop -- Henry's, Z's, or the Bourgeois Pig -- I end up at, it's always the same ever since free WiFi came on the scene. There are more laptops than coffee mugs, and never enough places to sit. But I'm as bad as the rest. What with free wireless Internet access and a cell phone, well, I haven't been in the office for year or so now, and even the concept of a home-office is becoming more remote.

When Seeing Is Believing

Posted by Jon Erickson 10:26 AM | February 26, 2009

So you aren't ready to buy into this multicore and parallelization stuff until you're able to see its benefits with your own eyes? If that's the case, then take a couple of minutes to watch this pair of YouTube videos that Gaston Hillar has prepared as part of his book C# 2008 and 2005 Threaded Programming: Beginner's Guide.

Posted by Jack Woehr

Open Sourcer Explores Intel MulticoreTools on Windows, Barely Lives to Tell Tale


An inveterate open-sourcer, I'm making an uneasy peace with Microsoft Windows for the purpose of exploring the tools Intel has made available for parallelization of applications running on multicore platforms. I have used and verbally abused Windows in every release since Windows 2.1. Thus I am no stranger, but Windows has not been a C/C++ development environment for me since the 1990's, though I test and run my Java stuff on Windows.

So, d'oh, of course I'm looking for the simplest way to do this ...

Going Parallell

Part 2: So who's really writing parallel applications?
Posted by Stephen Blair-chappell 05:20 AM | March 4, 2009

In a crazy moment sometime ago I forked out a few UK Pounds registering a url how-parallel-is-your-software.com (not the real address). The plan was to use the site to let people register any applications they found that ran parallel. Perhaps even run a competition to see who could find the most parallel commercial application. Maybe this would be the route to me becoming the next dotcom millionaire! I never had the nerve to bring the idea to life. I suspect that the moment I published anything every lawyer in town would be knocking at my door.

search Space

search Space ... the final frontier
Posted by Cameron Hughes, Tracey Hughes 02:56 PM | March 4, 2009

NP/NP complete and AI-complete problems are problems with huge or even infinite search or state spaces. The search or state space is a graph (or other representation) that contains all of the possible states (including the initial and goal states of the problem) of the domain of the initial problem. An example of a huge search space is all the nodes on the Internet ...

Multicore and Power Consumption:

Ask James About It
Posted by Jon Erickson 01:52 PM | March 6, 2009

Power naps. Now there's something I can relate to. No, not because I get a few minutes of shut-eye in the middle of the afternoon, but because I was just reading about this topic in The Problem of Power Consumption in Servers. The problem, of course, is that data centers are energy hogs, costing money and squander resources.

Events

* The U.S. government lodges a protest with the Chinese government after five Chinese ships "harassed" the USNS Impeccable in the South China Sea. (BBC)
* United States President Barack Obama lifts Bush administration restrictions on embryonic stem cell research. (Reuters)
* Argentina and Chile reject British claims over Antarctic territory and the seabed. (Sky News)
* North Korea promises to retaliate if its "satellite" launch is intercepted, saying interference would mean war. (CNN)
* Sudanese opposition leader Hassan Turabi is released after previously suggesting President Omar al-Bashir should give himself up. (AP)
* The Sri Lankan military claims it has killed 180 LTTE fighters carrying out a wave of counterattacks. (Reuters)
* Bombs explode in Qinghai, China, damaging police cars after a clash with several people. (AP)
* The Japanese economy posts a record deficit of 172.8 billion yen. (Press Association)
* Zimbabwean Prime Minister Morgan Tsvangirai rules out foul play in a car accident that killed his wife. (Guardian)
* Former Israeli President Moshe Katsav is to be charged with sex offences. (Bloomberg)
* Madagascar's government announces it will take "military measures" against mutinying soldiers. (Reuters)
* An Ilyushin Il-76 carrying equipment to the African Mission in Somalia (AMSOM) crashes into Lake Victoria shortly after takeoff from Entebbe International Airport, likely killing all eleven aboard. (UGpulse)
* Work begins to remove the wreckage of Turkish Airlines Flight 1951 from Amsterdam's Schiphol Airport. (World Bulletin)
* The loss of silicon-carrying ship MV Ibn al-Battuta off Safaga, Egypt leaves around a dozen missing or dead, with reports on numbers conflicting. (AFP) (CNN) (Xinhua)

recycle time Term of the Day

Previous Terms-of-the-Day
Last modified: Thursday, December 18, 2008


The phrase used to mean the amount of time a digital camera requires to reset the flash between one photo and the next. A longer recycle time makes it more difficult to capture action or time lapse shots. May also be called lag time or refresh rate.

See also "The Digital Camera Picture" in Webopedia's Quick Reference section.

Processor

Processor may refer to:

In computing:

* Central processing unit (CPU), the part of a computer that interprets instructions, in case of a multi-core processor it refers to multiple CPU's.
* Microprocessor, a CPU on one chip as part of a microcomputer
* Graphics processing unit (GPU / VPU), a dedicated graphics rendering device for a personal computer or game console

VPU (Visual / Video Processing Unit)

* Physics processing unit (PPU), a dedicated microprocessor designed to handle the calculations of physics
* Digital signal processor, a specialized microprocessor designed specifically for digital signal processing
* Network processor, a microprocessor specifically targeted at the networking application domain
* Front end processor, a helper processor for communication between a host computer and other devices
* Coprocessor
o Arithmetic logic unit
o Floating point unit
* Data processor, a system that translates or converts between different data formats
* Word processor, a computer application used for the production of printable material
* Audio processor, used in studios and radio stations

TYPES OF RAM

Top L-R, DDR2 with heat-spreader, DDR2 without heat-spreader, Laptop DDR2, DDR, Laptop DDR
1 Megabit chip - one of the last models developed by VEB Carl Zeiss Jena in 1989

Modern types of writable RAM generally store a bit of data in either the state of a flip-flop, as in SRAM (static RAM), or as a charge in a capacitor (or transistor gate), as in DRAM (dynamic RAM), EPROM, EEPROM and Flash. Some types have circuitry to detect and/or correct random faults called memory errors in the stored data, using parity bits or error correction codes. RAM of the read-only type, ROM, instead uses a metal mask to permanently enable/disable selected transistors, instead of storing a charge in them.

As both SRAM and DRAM are volatile, other forms of computer storage, such as disks and magnetic tapes, have been used as persistent storage in traditional computers. Many newer products instead rely on flash memory to maintain data when not in use, such as PDAs or small music players. Certain personal computers, such as many rugged computers and netbooks, have also replaced magnetic disks with flash drives. With flash memory, only the NOR type is capable of true random access, allowing direct code execution, and is therefore often used instead of ROM; the lower cost NAND type is commonly used for bulk storage in memory cards and solid-state drives.

[edit] Memory hierarchy

Many computer systems have a memory hierarchy consisting of CPU registers, on-die SRAM caches, external caches, DRAM, paging systems, and virtual memory or swap space on a hard drive. This entire pool of memory may be referred to as "RAM" by many developers, even though the various subsystems can have very different access times, violating the original concept behind the random access term in RAM. Even within a hierarchy level such as DRAM, the specific row, column, bank, rank, channel, or interleave organization of the components make the access time variable, although not to the extent that rotating storage media or a tape is variable. The overall goal of using a memory hierarchy is to obtain the higher possible average access performance while minimizing the total cost of entire memory system. (Generally, the memory hierarchy follows the access time with the fast CPU registers at the top and the slow hard drive at the bottom.)

In many modern personal computers, the RAM comes in an easily upgraded form of modules called memory modules or DRAM modules about the size of a few sticks of chewing gum. These can quickly be replaced should they become damaged or too small for current purposes. As suggested above, smaller amounts of RAM (mostly SRAM) are also integrated in the CPU and other ICs on the motherboard, as well as in hard-drives, CD-ROMs, and several other parts of the computer system.

[edit] Swapping

If a computer becomes low on RAM during intensive application cycles, the computer can perform an operation known as "swapping". When this occurs, the computer temporarily uses hard drive space as additional memory. Constantly relying on this type of backup memory is called thrashing, which is generally undesirable because it lowers overall system performance.

[edit] Other uses of the "RAM" term

Other physical devices with read–write capability can have "RAM" in their names: for example, DVD-RAM. "Random access" is also the name of an indexing method: hence, disk storage is often called "random access"[citation needed] because the reading head can move relatively quickly from one piece of data to another, and does not have to read all the data in between. However the final "M" is crucial: "RAM" (provided there is no additional term as in "DVD-RAM") always refers to a solid-state device.

[edit] RAM disks

Software can "partition" a portion of a computer's RAM, allowing it to act as a much faster hard drive that is called a RAM disk. Unless the memory used is non-volatile, a RAM disk loses the stored data when the computer is shut down. However, volatile memory can retain its data when the computer is shut down if it has a separate power source, usually a battery.

[edit] Shadow RAM

Sometimes, the contents of a ROM chip are copied to SRAM or DRAM to allow for shorter access times (as ROM may be slower). The ROM chip is then disabled while the initialized memory locations are switched in on the same block of addresses (often write-protected). This process, sometimes called shadowing, is fairly common in both computers and embedded systems.

As a common example, the BIOS in typical personal computers often has an option called “use shadow BIOS” or similar. When enabled, functions relying on data from the BIOS’s ROM will instead use DRAM locations (most can also toggle shadowing of video card ROM or other ROM sections). Depending on the system, this may or may not result in increased performance. On some systems the benefit may be hypothetical because the BIOS is not used after booting in favor of direct hardware access. Of course, somewhat less free memory is available when shadowing is enabled.[2]

[edit] Recent developments

Several new types of non-volatile RAM, which will preserve data while powered down, are under development. The technologies used include carbon nanotubes and the magnetic tunnel effect. In summer 2003, a 128 KB (128 × 210 bytes) magnetic RAM (MRAM) chip was manufactured with 0.18 µm technology. In June 2004, Infineon Technologies unveiled a 16 MB (16 × 220 bytes) prototype again based on 0.18 µm technology. Nantero built a functioning carbon nanotube memory prototype 10 GB (10 × 230 bytes) array in 2004. Whether some of these technologies will be able to eventually take a significant market share from either DRAM, SRAM, or flash-memory technology, however, remains to be seen.

Since 2006, "Solid-state drives" (based on flash memory) with capacities exceeding 642 gigabytes and performance far exceeding traditional disks have become available. This development has started to blur the definition between traditional random access memory and "disks", dramatically reducing the difference in performance. Also in development is research being done in the field of plastic magnets, which switch magnetic polarities based on light.

[edit] Memory wall

The "memory wall" is the growing disparity of speed between CPU and memory outside the CPU chip. An important reason for this disparity is the limited communication bandwidth beyond chip boundaries. From 1986 to 2000, CPU speed improved at an annual rate of 55% while memory speed only improved at 10%. Given these trends, it was expected that memory latency would become an overwhelming bottleneck in computer performance. [3]

Currently, CPU speed improvements have slowed significantly partly due to major physical barriers and partly because current CPU designs have already hit the memory wall in some sense. Intel summarized these causes in their Platform 2015 documentation (PDF)

“First of all, as chip geometries shrink and clock frequencies rise, the transistor leakage current increases, leading to excess power consumption and heat (more on power consumption below). Secondly, the advantages of higher clock speeds are in part negated by memory latency, since memory access times have not been able to keep pace with increasing clock frequencies. Third, for certain applications, traditional serial architectures are becoming less efficient as processors get faster (due to the so-called Von Neumann bottleneck), further undercutting any gains that frequency increases might otherwise buy. In addition, partly due to limitations in the means of producing inductance within solid state devices, resistance-capacitance (RC) delays in signal transmission are growing as feature sizes shrink, imposing an additional bottleneck that frequency increases don't address.”

The RC delays in signal transmission were also noted in Clock Rate versus IPC: The End of the Road for Conventional Microarchitectures which projects a maximum of 12.5% average annual CPU performance improvement between 2000 and 2014. The data on Intel Processors clearly shows a slowdown in performance improvements in recent processors. However, Intel's new processors, Core 2 Duo (codenamed Conroe) show a significant improvement over previous Pentium 4 processors; due to a more efficient architecture, performance increased while clock rate actually decreased.

[edit] Security concerns

Contrary to simple models (and perhaps common belief), the contents of modern SDRAM modules are not lost immediately when the computer is shut down; instead, the contents fade away, a process that takes only seconds at room temperatures, but which can be extended to minutes at low temperatures. It is therefore possible to get hold of an encryption key if it were stored in ordinary working memory (i.e. the SDRAM modules).[4] This is sometimes referred to as a cold boot attack.

[edit] See also
Sister project Wikimedia Commons has media related to: RAM

* CAS latency (CL)
* Dual-channel architecture
* ECC (Error-correcting code)
* Registered/buffered memory
* RAM parity

[edit] Notes and references

1. ^ Strictly speaking, modern types of DRAM are therefore not truly (or technically) random access, as data are read in burst; the name DRAM has stuck however.
2. ^ "Shadow Ram" (HTML). http://hardwarehell.com/articles/shadowram.htm. Retrieved on 2007-07-24.
3. ^ The term was coined in Hitting the Memory Wall: Implications of the Obvious (PDF).
4. ^ Cold Boot Attacks on Encryption Keys

[edit] External links
Retrieved from "http://en.wikipedia.org/wiki/Random-access_memory"
Categories: Computer memory
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history of RAM

History

An early type of widespread writable random access memory was the magnetic core memory, developed from 1949 to 1952, and subsequently used in most computers up until the development of the static and dynamic integrated RAM circuits in the late 1960s and early 1970s. Before this, computers used relays, delay line memory or various kinds of vacuum tube arrangements to implement "main" memory functions (i.e., hundreds or thousands of bits), some of which were random access, some not. Latches built out of vacuum tube triodes, and later, out of discrete transistors, were used for smaller and faster memories such as registers and (random access) register banks. Prior to the development of integrated ROM circuits, permanent (or read-only) random access memory was often constructed using semiconductor diode matrices driven by address decoders.

RAM

Random-access memory is a form of computer data storage. Today it takes the form of integrated circuits that allows the stored data to be accessed in any order (i.e., at random). The word random thus refers to the fact that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data.[1]

This contrasts with storage mechanisms such as tapes, magnetic discs and optical discs, which rely on the physical movement of the recording medium or a reading head. In these devices, the movement takes longer than the data transfer, and the retrieval time varies depending on the physical location of the next item.

The word RAM is mostly associated with volatile types of memory (such as DRAM memory modules), where the information is lost after the power is switched off. However, many other types of memory are RAM as well (i.e., Random Access Memory), including most types of ROM and a kind of flash memory called NOR-Flash.