- Great Painters
- Accounting
- Fundamentals of Law
- Marketing
- Shorthand
- Concept Cars
- Videogames
- The World of Sports

- Blogs
- Free Software
- Google
- My Computer

- PHP Language and Applications
- Wikipedia
- Windows Vista

- Education
- Masterpieces of English Literature
- American English

- English Dictionaries
- The English Language

- Medical Emergencies
- The Theory of Memory
- The Beatles
- Dances
- Microphones
- Musical Notation
- Music Instruments
- Batteries
- Nanotechnology
- Cosmetics
- Diets
- Vegetarianism and Veganism
- Christmas Traditions
- Animals

- Fruits And Vegetables


  1. Adobe Reader
  2. Adware
  3. Altavista
  4. AOL
  5. Apple Macintosh
  6. Application software
  7. Arrow key
  8. Artificial Intelligence
  9. ASCII
  10. Assembly language
  11. Automatic translation
  12. Avatar
  13. Babylon
  14. Bandwidth
  15. Bit
  16. BitTorrent
  17. Black hat
  18. Blog
  19. Bluetooth
  20. Bulletin board system
  21. Byte
  22. Cache memory
  23. Celeron
  24. Central processing unit
  25. Chat room
  26. Client
  27. Command line interface
  28. Compiler
  29. Computer
  30. Computer bus
  31. Computer card
  32. Computer display
  33. Computer file
  34. Computer games
  35. Computer graphics
  36. Computer hardware
  37. Computer keyboard
  38. Computer networking
  39. Computer printer
  40. Computer program
  41. Computer programmer
  42. Computer science
  43. Computer security
  44. Computer software
  45. Computer storage
  46. Computer system
  47. Computer terminal
  48. Computer virus
  49. Computing
  50. Conference call
  51. Context menu
  52. Creative commons
  53. Creative Commons License
  54. Creative Technology
  55. Cursor
  56. Data
  57. Database
  58. Data storage device
  59. Debuggers
  60. Demo
  61. Desktop computer
  62. Digital divide
  63. Discussion groups
  64. DNS server
  65. Domain name
  66. DOS
  67. Download
  68. Download manager
  69. DVD-ROM
  70. DVD-RW
  71. E-mail
  72. E-mail spam
  73. File Transfer Protocol
  74. Firewall
  75. Firmware
  76. Flash memory
  77. Floppy disk drive
  78. GNU
  79. GNU General Public License
  80. GNU Project
  81. Google
  82. Google AdWords
  83. Google bomb
  84. Graphics
  85. Graphics card
  86. Hacker
  87. Hacker culture
  88. Hard disk
  89. High-level programming language
  90. Home computer
  91. HTML
  92. Hyperlink
  93. IBM
  94. Image processing
  95. Image scanner
  96. Instant messaging
  97. Instruction
  98. Intel
  99. Intel Core 2
  100. Interface
  101. Internet
  102. Internet bot
  103. Internet Explorer
  104. Internet protocols
  105. Internet service provider
  106. Interoperability
  107. IP addresses
  108. IPod
  109. Joystick
  110. JPEG
  111. Keyword
  112. Laptop computer
  113. Linux
  114. Linux kernel
  115. Liquid crystal display
  116. List of file formats
  117. List of Google products
  118. Local area network
  119. Logitech
  120. Machine language
  121. Mac OS X
  122. Macromedia Flash
  123. Mainframe computer
  124. Malware
  125. Media center
  126. Media player
  127. Megabyte
  128. Microsoft
  129. Microsoft Windows
  130. Microsoft Word
  131. Mirror site
  132. Modem
  133. Motherboard
  134. Mouse
  135. Mouse pad
  136. Mozilla Firefox
  137. Mp3
  138. MPEG
  139. MPEG-4
  140. Multimedia
  141. Musical Instrument Digital Interface
  142. Netscape
  143. Network card
  144. News ticker
  145. Office suite
  146. Online auction
  147. Online chat
  148. Open Directory Project
  149. Open source
  150. Open source software
  151. Opera
  152. Operating system
  153. Optical character recognition
  154. Optical disc
  155. output
  156. PageRank
  157. Password
  158. Pay-per-click
  159. PC speaker
  160. Peer-to-peer
  161. Pentium
  162. Peripheral
  163. Personal computer
  164. Personal digital assistant
  165. Phishing
  166. Pirated software
  167. Podcasting
  168. Pointing device
  169. POP3
  170. Programming language
  171. QuickTime
  172. Random access memory
  173. Routers
  174. Safari
  175. Scalability
  176. Scrollbar
  177. Scrolling
  178. Scroll wheel
  179. Search engine
  180. Security cracking
  181. Server
  182. Simple Mail Transfer Protocol
  183. Skype
  184. Social software
  185. Software bug
  186. Software cracker
  187. Software library
  188. Software utility
  189. Solaris Operating Environment
  190. Sound Blaster
  191. Soundcard
  192. Spam
  193. Spamdexing
  194. Spam in blogs
  195. Speech recognition
  196. Spoofing attack
  197. Spreadsheet
  198. Spyware
  199. Streaming media
  200. Supercomputer
  201. Tablet computer
  202. Telecommunications
  203. Text messaging
  204. Trackball
  205. Trojan horse
  206. TV card
  207. Unicode
  208. Uniform Resource Identifier
  209. Unix
  210. URL redirection
  211. USB flash drive
  212. USB port
  213. User interface
  214. Vlog
  215. Voice over IP
  216. Warez
  217. Wearable computer
  218. Web application
  219. Web banner
  220. Web browser
  221. Web crawler
  222. Web directories
  223. Web indexing
  224. Webmail
  225. Web page
  226. Website
  227. Wiki
  228. Wikipedia
  229. WIMP
  230. Windows CE
  231. Windows key
  232. Windows Media Player
  233. Windows Vista
  234. Word processor
  235. World Wide Web
  236. Worm
  237. XML
  238. X Window System
  239. Yahoo
  240. Zombie computer

This article is from:

All text is available under the terms of the GNU Free Documentation License: 

Random access memory

From Wikipedia, the free encyclopedia


Random access memory (usually known by its acronym, RAM) is a type of data store used in computers that allows the stored data to be accessed in any order — that is, at random, not just in sequence. In contrast, other types of memory devices (such as magnetic tapes, disks, and drums) can access data on the storage medium only in a predetermined order due to constraints in their mechanical design.

It costs practically the same time to access any piece of data stored in a RAM chip. In contrast, disks and the like need a short time to retrieve a piece of data if it happens to be close to the current position of the read head, and a long time if the data is far away and the head needs to be repositioned considerably.

Generally, RAM in a computer is considered main memory or primary storage: the working area used for loading, displaying and manipulating applications and data. This type of RAM is usually in the form of integrated circuits (ICs). These are commonly called memory sticks or RAM sticks because they are manufactured as small circuit boards with plastic packaging and are about the size of a few sticks of chewing gum. Most personal computers have slots for adding and replacing memory sticks.

Most RAM can be both written to and read from, so "RAM" is often used interchangeably with "read-write memory." In this sense, RAM is the "opposite" of ROM, but in a more true sense, of sequential access memory.


Computers use RAM to hold the program code and data during computation. A defining characteristic of RAM is that all memory locations can be accessed at almost the same speed. Most other technologies have inherent delays for reading a particular bit or byte.

Many types of RAM are volatile, which means that unlike some other forms of computer storage such as disk storage and tape storage, they lose all data when the computer is powered down. Modern RAM generally stores a bit of data as either a charge in a capacitor, as in dynamic RAM, or the state of a flip-flop, as in static RAM.

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.

Some types of RAM can detect or correct random faults called memory errors in the stored data, using RAM parity.


A four-megabyte RAM card measuring about twenty-two by fifteen inches (55.8 by 38.1 centimeters); made for the VAX 8600 minicomputer (circa 1986).  Dual in-line package (DIP)  Integrated circuits populate nearly the whole board; the RAM chips are in the majority located in the rectangular areas to the left and right.
A four-megabyte RAM card measuring about twenty-two by fifteen inches (55.8 by 38.1 centimeters); made for the VAX 8600 minicomputer (circa 1986). Dual in-line package (DIP)  Integrated circuits populate nearly the whole board; the RAM chips are in the majority located in the rectangular areas to the left and right.

Early main memory systems built from vacuum tubes behaved much like modern RAM, except that they failed frequently. Core memory, which used wires attached to small ferrite electromagnetic cores, also had roughly equal access time. The term “core” is still used by some programmers to describe the RAM main memory of a computer. The basic concepts of tube and core memory are used in modern RAM implemented with integrated circuits.

Alternative primary storage mechanisms usually involved a non-uniform delay for memory access. Delay line memory used a sequence of sound wave pulses in mercury-filled tubes to hold a series of bits. Drum memory acted much like the modern hard disk, storing data magnetically in continuous circular bands. (See primary storage for a greater discussion of these alternatives and others.)

Recent developments

Currently, several types of non-volatile RAM are under development, which will preserve data while powered down. The technologies used include carbon nanotubes and the magnetic tunnel effect.

In summer 2003, a 128 kB magnetic RAM chip was introduced, which was manufactured with 0.18 ΅m technology. The core technology of MRAM is based on the magnetic tunnel effect. In June of 2004, Infineon Technologies unveiled a 16 MB prototype again based on 0.18 ΅m technology.

As for carbon nanotube memory, a high-tech startup Nantero built a functioning prototype 10 GB array in 2004.

The Memory Wall

The term "memory wall", first officially coined in Hitting the Memory Wall: Implications of the Obvious (PDF), refers to the growing disparity between CPU and memory speed. 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.

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). Intel's new Tri-Gate could solve this problem. 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, 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 (codenamed Conroe) shows a significant improvement over previous Pentium 4 processors.

Shadow RAM

Shadow RAM is RAM whose contents are copied from read-only memory (ROM) to allow shorter access times [1], as ROM is in general slower than RAM. The original ROM is disabled and the new location on the RAM is write-protected. This process is called shadowing.

DRAM packaging

For economical reasons, the large (main) memories found in personal computers, workstations, and non-handheld game-consoles (such as playstation and xbox) normally consists of dynamic RAM (DRAM). Other parts of the computer, such as cache memories and data buffers in hard disks, normally use static RAM (SRAM).

Common DRAM packages
Common DRAM packages

General DRAM packaging formats

Dynamic random access memory (DRAM) is produced as integrated circuits (ICs) bonded and mounted into plastic packages with metal pins for connection to control signals and buses. Today, these DRAM packages are in turn often assembled into plug-in modules for easier handling. Some standard module types are:

  • DRAM chip (Integrated Circuit or IC)
    • Dual in-line Package (DIP)
  • DRAM (memory) modules
    • Single In-line Pin Package (SIPP)
    • Single in-line memory module (SIMM)
    • Dual in-line memory module (DIMM)
    • Rambus modules are technically DIMMs, but are usually referred to as RIMMs due to their proprietary slot.
    • Small outline DIMM (SO-DIMM). Smaller version of the DIMM, used in laptops. Comes in versions with:
      • 72 pins (32-bit)
      • 144 pins (64-bit)
      • 200 pins (72-bit)
    • Small outline RIMM (SO-RIMM). Smaller version of the RIMM, used in laptops.
  • Stacked v. non-stacked RAM modules
    • Stacked RAM chips use two RAM wafers that are stacked on top of each other. This allows large module (like a 512mb or 1Gig SO-DIMM) to be manufactured using cheaper low density wafers. Stacked chip modules draw more power.

Common DRAM modules

Common DRAM packages as illustrated to the right, from top to bottom:

  1. DIP 18-pin (DRAM chip, usually pre-FPRAM)
  2. SIPP (usually FPRAM)
  3. SIMM 30-pin (usually FPRAM)
  4. SIMM 72-pin (so-called "PS/2 SIMM", usually EDO RAM)
  5. DIMM 168-pin (SDRAM)
  6. DIMM 184-pin (DDR SDRAM)
  7. DIMM 240-pin (DDR2 SDRAM) - (DRAM not pictured to the right.)

History of DRAM modules used in PCs

How RAM Works An interactive application to learn more about RAM.

DRAM-module manufacturers

Major manufacturers of DRAM modules as of 2006:

See also

  • DIMM
  • Registered/Buffered memory
  • Compact Flash
  • Static RAM (SRAM)
  • Non-Volatile RAM (NVRAM)
  • Dynamic RAM (DRAM)
    • Fast Page Mode DRAM
    • EDO RAM or Extended Data Out DRAM
    • XDR DRAM
    • SDRAM or Synchronous DRAM
      • DDR SDRAM or Double Data Rate Synchronous DRAM; now being replaced by DDR2 SDRAM
      • RDRAM or Rambus DRAM

External links

  • What kind of RAM do I have? – From Darrell's Computer Help and Information
  • "How RAM Works" – Article by Jeff Tyson and Dave Coustan
  • Memory Basics (Flash) – From RAM
  • How to Install PC Memory Guides
  • Memory Installation FAQ's
  • Ultimate Memory Guide – From Kingston
  • Glossary of Memory and Memory Terms
Retrieved from ""