Parity Error Ecc
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required the used of parity memory, since it was designed by engineers familiar with the needs of businesses who used the large mainframe computers. The semiconductors produced at that
Ecc Vs Parity
time were not considered to be as reliable as today's chips are, and so difference between parity and ecc there existed a need to be sure that every memory access contained accurate data. Businesses such as banks, airlines, stock brokers, etc. how ecc memory works all needed to be sure that no errors were introduced by faulty memory chips (hard errors) or by random electronic ‘glitches' that could alter the data (soft errors). Apple took a slightly different approach to
Non Parity Ram
things. They figured that the average home user of their product really wouldn't be affected by the occassional random error that might be introduced, and so elected to design their machines to run using non-parity memory modules. This allowed them to reduce the cost of their machines, since non-parity modules require fewer chips. At this time, memory was very expensive, and the elimination of the parity chip reduced the cost
What Is A Parity Error
by approximately 12% (quite significant when 4MB of memory cost several hundred dollars). IBM PC clone manufacturers soon began to recognize that they could better compete if they provided systems that used non-parity memory, so some 386 machines began to appear with this ‘feature'. When the 486 systems began to be produced, the vast majority of them were using non-parity memory. To this day almost all systems sold contain non-parity memory unless parity is specifically requested. Only systems that are considered to be handling ‘mission critical' data will contain parity (or ECC) memory, such as servers. Since the soft error rate for today's A-grade chips is about once every ten years (or better), it seems to makes sense that non-parity is the norm. In addition, with the majority of systems running Windows95 or Windows98, where data integrity cannot be guaranteed, ECC will really only lessen the probability of a data error. On the other hand, for those using operating systems that are a bit more ‘robust', memory prices have dropped so significantly that the additional cost of ECC memory usually amounts to about $15.00, assuming a 128MB module. How Error Checking Works Parity checking is a rather simple method of detecting memory errors, without any correction capabilities. Basically every b
The PC Guide Tip Jar. Visa/MC/Paypal accepted. View over 750 of my fine art photos any time for free at DesktopScenes.com! [ The PC Guide | Systems and Components Reference Guide | System Memory parity vs non parity mental health | Memory Errors, Detection and Correction ] Non-Parity, Parity and ECC Memory
Memory modules haveError Correction Code
traditionally been available in two basic flavors: non-parity and parity. (Actually, some sizes and styles are only available in non-parity, but most ecc encryption are available either way.) Non-parity is "regular" memory--it contains exactly one bit of memory for every bit of data to be stored. 8 bits are used to store each byte of data. Parity memory adds an extra http://www.realworldtech.com/parity-and-ecc-explored/ single bit for every eight bits of data, used only for error detection and correction. 9 bits of data are used to store each byte. The table below shows a summary of the different common module sizes and their bit widths: Module Type Bit Width of Non-Parity SIMM Bit Width of Parity SIMM 30-Pin SIMM 8 bits 9 bits 72-Pin SIMM 32 bits 36 bits 168-Pin DIMM 64 bits 72 bits Parity memory http://www.pcguide.com/ref/ram/errParity-c.html can be used for parity checking, a basic form of error detection, on PCs that support it. It can also be used for an advanced form of error detection and correction called ECC on Pentium class or later systems that support ECC. Non-parity memory provides no error detection capabilities at all unless these are provided through external circuitry (which is basically never done on regular PCs.) In recent years, a new type of memory has become popular: ECC memory. As the name implies, this is memory specifically designed to allow the use of ECC on modern systems that have a chipset that supports it, much the way that parity memory can on some systems. Due to the fact that both types of memory support ECC, there has been a great deal of confusion about the difference between ECC and parity memory, especially since they often are quoted with the same specifications. The biggest difference between the two types of memory is that ECC memory works in ECC mode and so does parity memory, but ECC memory does not work in plain parity checking mode. The reason is that while an ECC module contains one extra bit per byte the way parity ones do, the extra bits cannot be individually accessed, which is required for parity operation. To make m
in random access memory, and the subsequent comparison of the stored and the computed parity to detect whether a data error has occurred. The parity bit was originally stored in additional individual memory chips; with the introduction of plug-in DIMM, SIMM, etc. http://en.wikipedia.org/wiki/RAM_parity modules, they became available in non-parity and parity (with an extra bit per byte, storing 9 bits for every 8 bits of actual data) versions. Contents 1 History 2 Memory errors 3 Error correction 3.1 ECC type RAM 4 See also 5 References History[edit] Early computers sometimes required the use of parity RAM, and parity-checking could not be disabled. A parity error typically caused the machine to halt, with loss of unsaved data; this is usually a better option parity error than saving corrupt data. Logic parity RAM, also known as fake parity RAM, is non-parity RAM that can be used in computers that require parity RAM. Logic parity RAM recalculates an always-valid parity bit each time a byte is read from memory, instead of storing the parity bit when the memory is written to; the calculated parity bit, which will not reveal if the data has been corrupted (hence the name "fake parity"), is presented to the parity-checking logic. It parity error ecc is a means of using cheaper 8-bit RAM in a system designed to use only 9-bit parity RAM. Memory errors[edit] In the 1970s-80s, RAM reliability was often less-than-perfect; in particular, the 4116 DRAMs which were an industry standard from 1975 to 1983 had a considerable failure rate as they used triple voltages (-5, +5, and +12) which resulted in high operating temperatures. By the mid-1980s, these had given way to single voltage DRAM such as the 4164 and 41256 with the result of improved reliability. However, RAM did not achieve modern standards of reliability until the 1990s. Since then errors have become less visible as simple parity RAM has fallen out of use; either they are invisible as they are not detected, or they are corrected invisibly with ECC RAM. Modern RAM is believed, with much justification, to be reliable, and error-detecting RAM has largely fallen out of use for non-critical applications. By the mid-1990s, most DRAM had dropped parity checking as manufacturers felt confident that it was no longer necessary. Some machines that support parity or ECC allow checking to be enabled or disabled in the BIOS, permitting cheaper non-parity RAM to be used. If parity RAM is used the chipset will usually use it to implement error correction, rather than halting the machine on a single-bit parity error. However, as discussed in the article on ECC memory, errors, while not everyday events, are not negligib