RAM ( Random Access Memory of English , often abbreviated to RAM ) is a type of memory that allows both reading and writing, used as primary memory in electronic systems digitais.1 The RAM is an essential component not only in personal computers , but on any type of computer , it is basically where the programs are stored basic operational . As much as there is storage space available in the form of a HDD or flash memory , is always required a certain amount of RAM and of course, the more memory , the better the performance , since the programs tend to develop with passage of time and research científica.2 The term random access identifies the ability to access any position and at any time , as opposed to sequential access , imposed by some storage devices such as magnetic tapes . The name is not really appropriate, since other types of memory ( such as ROM ) also allow random access to its contents . A better name would be : Reading and Writing Memory , which is expressed in computer programming . Although the concept of working memory random access be quite broad , the term is currently used only to define an electronic device that implements it , since currently this memory is spread within the system itself from the current computer system ( so to speak " nervous " of the computer, such as human ) , basically a specific type of chip . In this case , it is also implied that is a volatile memory , that is, its contents are lost when power to the memory is turned off. The main memory of a computer based on the Von Neumann architecture consists of RAM . It is this memory that load running programs and their user data . Since it is volatile memory , your data is lost when the computer is turned off . To prevent losing data , you should save the information to support nonvolatile , like hard rígido.3 Contents [ hide ] 1 Introduction 2 History 3 Types 4 Capacity and Speed 5 Cache 6 Bibliography 7 References 8 External links Introduction [ edit] It is used by the processor to store the files and programs that are being processed . The amount of available RAM has a large effect on performance , since without a sufficient amount of it the system will use virtual memory, which is slow . The main characteristic of RAM is that it is volatile , ie , the data are lost when you restart the computer. By connecting it to redo the entire loading process , in which the operating system and applications used are transferred from HD to memory , which can be executed by processador.4 The memory chips are sold in the form of memory sticks . There combs of various capacities , and the plates usually have two or three slots available . No way to install a comb of 1 GB along with 512 MB which came in the micro to have a total of 1536 MB for exemplo.4 History [ edit] Chip 1 Megabyte - One of the last models developed by VEB Carl Zeiss Jena in 1989 . The first type of RAM was the magnetic core , developed from 1955 to 1975 and subsequently used in most computers to the development and adoption of static and dynamic integrated RAM circuits in the late 1960s and early 1970.5 Types [ edit] Example memory writable volatile random access : Synchronous Dynamic RAM modules , primarily used as main memory in personal computers , workstations and servers . There are basically two types of memory in use : SDR and DDR . The SDRs are the traditional type , where the memory controller performs only a read per cycle , while the DDR are faster , as do two reads per cycle. The performance will less than double , because the initial access is still taking the same time, but greatly improves . The SDR memory sticks are used in old PCs : Pentium II and Pentium III and the first Socket A Athlons and Durons Why not be more manufactured, they are now much more rare and expensive than DDR , something similar to what happened with the old combs of 72 routes , used at the time of the Pentium 1.4 It is easy to differentiate the combs SDR and DDR , as the SDR have two bevels and only one DDR . This difference makes it not also possible to change the balls , by mistake fitting a comb in a DDR motherboard that uses SDR and vice versa . More recently , there have been a new migration , with the introduction of DDR2 memory sticks . In them , the bus memory access works at twice the frequency of the memory chips themselves. This allows them to be carried out two read operations per cycle , accessing two different addresses . As the ability to perform two transfers per cycle introduced in DDR was preserved , and DDR2 are able to perform a total of four read operations per cycle , an impressive mark . There are also some secondary benefits , such as lower power consumption , useful in notebooks.4 The DDR2 memory sticks are incompatible with older motherboards . They have a larger number of contacts ( a total of 240 , against 184 combs DDR ) , and the central groove is positioned differently , so it is not possible to install them in older cards by mistake . Many combs are sold with a metal sink , which helps in heat dissipation and allows modules to operate at frequencies altas.4 Capacity and Speed [ edit] The memory capacity is measured in bytes , Kilobyte ( KB = 1024 or 1 210 Bytes ) , Megabyte ( 1 MB = 1024 KB or 220 Bytes ) Gigabyte ( 1 GB = 1024 MB or 230 Bytes ) and terabyte ( 1 TB = 1024GB or 2 30 Bytes ) .6 The operating speed of a memory is measured in Hz or MHz This value is related to the number of blocks of data that can be transferred during one second. There are however some RAM memories that can make two transfers data in the same clock cycle , doubling taxxa transfer information to the same working frequency . Furthermore , the placement of the memories in parallel ( the property of certain systems architecture ) enables to multiply the apparent speed of the memory. Cache [ edit] Top LR , DDR2 with heat sink , DDR2 without heat sink , Laptop DDR2 , DDR , DDR Laptop Anyway , despite all the progress the RAM is still much slower than the processor . To mitigate the difference , are used two levels of cache , included in the CPU : L1 cache and L2 cache . The L1 cache is extremely fast , often working near native processor . In fact , the two work on the same frequency , but it takes a few clock cycles to the information stored in L1 reaches the processing units . In the case of the Pentium 4 , we arrive at the end to store already decoded instructions in L1 : they take up more space, but eliminate this initial time . In general , the faster the cache , it takes up more space and less can be included in the processor . That is why the Pentium 4 includes a total of only 20 KB L1 cache this ultra -fast , against the 128 KB cache slightly slower used in Sempron.4 Then comes the L2 cache, which is a little slower in terms of access time ( the time required to start the download ) and in bandwidth , but it is much more economical in terms of transistors , allowing it to be used in larger amount . The amount of L2 cache used varies according to the processor . While most models use only Sempron 256 KB , the more expensive models of the Core 2 Duo processors have 4MB memory completos.4 Parity is a method created to correct memory errors , is old , and only identifies errors , not corrects . Consists in adding a control bit at the end of each byte of memory. Memory parity It is a method created to correct memory errors . It is the oldest method , and only identifies errors not corrected , and consists in adding a control bit at the end of each byte of memory. The operation of checking the parity data is quite simple : they counted the number of "1" bits of each byte. If the number is even , the parity bit assumes a value of " 0 " and if odd , 9th bit assumes a value " 1 " . When requested by the processor , the data are checked by parity circuit that checks whether the number of "1" bits corresponds to bit filed on 9 . If detected change in the data, it sends a message to the processor error . The method is not completely effective since it is able to detect the alteration of a number of bits which maintains parity. If two bits return zero changed to one bits , the parity circuit would not notice the change in the data . Fortunately , the possibility of changing two or more bits at the same time is remote . The use of parity does not make the computer slower since the circuitry responsible for checking the data are independent of the rest of the system . Its only side effect is the enhancement of memory , rather than 8 bits per byte , 9 are replaced , making it about 12 to 60% more expensive . Device - ECC ( Error Correct Code ) - Code error correction . Detection code in which a combination of pulses prohibitive by accretion or loss of 1 bit indicates which bit is wrong . Besides the cost , parity does not allow correct errors , just identify them , which reduces its practical usefulness . The increase in the good level of reliability of the new memory modules made memories with parity fell into disuse .
Posted on: Wed, 09 Oct 2013 20:12:11 +0000
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