Module one / unit 4 Memory By Kenneth Ayebazibwe256774185458 / 256702555890 email@example.com
Objectives• On completion of this unit, you will be able to; – Distinguish RAM and ROM memory techniques – Describe the memory types SDRAM, RDRAM, DDR/ DDR2 and SRAM and give examples of how they are used – Identify DIMM and RIMM memory packaging for different technologies – Understand the characteristics of different memory types – Double sided – ECC – registered
Memory Types• RAM - Random Access Memory ROM - Read-Only Memory – RAM is the piece of memory where the programs and files you are using are stored, thus the files found in your RAM changes all the time (e.g MSN, Firefox, Word Docs, etc remains in RAM if you are using it). When your PC is switched off, data in your RAM is gone and cannot be recovered unless it has been saved on a permanent memory that is Hard Disk. ROM is the place where data that you cannot alter is stored, for example BIOS or Bootstrap Loader. ROM is used in the computer so that the processor does not have to look for important pieces of data when switched on, The processor just finds it in the ROM. You cannot edit files in ROM and data on it cannot be erased by turning off your PC
Types of RAM: How to Identify and their Specifications• There are many different types of RAM which have appeared over the years and it is often difficult knowing the difference between them both performance wise and visually identifying them.
FPM RAM• FPM RAM, which stands for Ã¢â‚¬Å“Fast Page Mode RAMÃ¢â‚¬Â (DRAM). The term Ã¢â‚¬Å“Fast Page ModeÃ ¢â‚¬Â) comes from the capability of memory being able to access data that is on the same page and can be done with less latency. Most 486 and Pentium based systems from 1995 and earlier use FPM Memory.•
EDO RAM• EDO RAM, which stands for Ã¢â‚¬Å“Extended Data Out RAMÃ¢â‚¬Â available for Pentium based systems. EDO is a modified form of FPM RAM which is commonly referred to as Ã¢â‚¬Å“Hyper Page ModeÃ¢â‚¬Âs . Extended Data Out refers to fact that the data output drivers on the memory module are not switched off when the memory controller removes the column address to begin the next cycle, unlike FPM RAM. Most early Penitum based systems use EDO.
SDRAM• SDRAM , which is short for Synchronous DRAM is a type of DRAM that runs in synchronization with the memory bus. Beginning in 1996 most Intel based chipsets began to support SDRAM which made it a popular choice for new systems in 2001. SDRAM is capable of running at 133MHz which is about three times faster than FPM RAM and twice as fast as EDO RAM. Most Pentium or Celeron systems purchased in 1999 have SDRAM.
DDR RAM• DDR RAM, which stands for Ã¢â‚¬Å“Double Data RateÃ ¢â‚¬ÂA which is a type of SDRAM and appeared first on the market around 2001 but didn’t catch on until about 2001 when the mainstream motherboards started supporting it. The difference between SDRAM and DDR RAM is that instead of doubling the clock rate it transfers data twice per clock cycle which effectively doubles the data rate. DDRRAM has become mainstream in the graphics card market and has become the memory standard.
Memory Packaging• Memory is available in various physical packaging. Roughly in order of their appearance, the major types of DRAM packaging include: – DIP (Dual Inline Pin Package)This package comprises a rectangular chip with a row of pins down each long side, making it resemble an insect. DIP was the most common DRAM package used in PCs through early 386 models. DIP chips were produced in Page Mode and Fast Page Mode, and are long obsolete. DIP packaging was also used for L2 cache memory on most 486 and some Pentium-class motherboards. DIP DRAM is useless nowadays. – SIPP (Single Inline Pin Package)This package turns a DIP chip on its side and extends all leads straight out one side, parallel to the plane of the chip. SIPPs were intended to allow memory to be installed more densely, and were used in a few 386SX systems, but they never caught on. SIPPs were produced in Page Mode and Fast Page Mode form, and are long obsolete.
– SIMM (Single Inline Memory Module)This package mounts multiple individual DRAM DIP chips on a small circuit board with a card- edge connector designed to fit a socket on the motherboard. Mainstream SIMMs have been manufactured in two form factors: • 30-pinThese SIMMs were used in a few 286 systems, most 386 systems, and some 486 systems, and were produced in Page Mode and Fast Page Mode form. Although they are still available, 30-pin SIMMs are obsolete. If you tear down an old system, any 30-pin SIMMs you salvage are too small and too slow to be useful. However, some laser printers do use them. • 72-pinThese SIMMs were used in some 386 systems, most 486 systems, and nearly all Pentium-class systems built before the advent of DIMMs. 72-pin SIMMs were produced in Fast Page Mode, EDO form, and BEDO form. When tearing down old systems, 72-pin SIMMs may be worth salvaging, as they can be used to expand the memory on a late- model Pentium or Pentium Pro system or to expand the memory in some laser printers.
• Figure shows a 72-pin SIMM (top) and a 30-pin SIMM. The 72-pin SIMM is keyed by the notch at the bottom right; the 30-pin SIMM by the notch at the bottom left. The holes on either side immediately above the bottom row of contacts are used by the slot retention mechanism to secure the SIMM in the slot. Although it may not be visible in the reproduction, the top SIMM uses gold contacts and the bottom SIMM tin contacts.
• DIMM (Dual Inline Memory Module)DIMMs are dual-side modules that use connectors on both sides of the circuit board. SDR-SDRAM DIMMs have 168 pins, but SDR-SDRAM is also available in 100- and 144-pin DIMMs. DDR-SDRAM is packaged in 184-pin DIMMs, which are physically similar to standard 168-pin SDR-SDRAM DIMMs, but have additional pins and different keying notch positions to prevent them from being interchanged. DDR-II DIMMs are similar to DDR DIMMs, but use a 232-pin connector. Only SDR-SDRAM, DDR-SDRAM, and EDO are commonly packaged as DIMMs.• SODIMM (Small Outline DIMM)A special package used in notebook computers and on some video adapters.• RIMMA Rambus RDRAM module. RIMM is a trade name rather than an acronym. RIMMs are physically similar to standard SDRAM DIMMs, except that the keying notches are in different locations. RDRAM is available in 168- pin and 184-pin modules. Early RDRAM motherboards used 168-pin RIMMs. Most current RDRAM motherboards use 184-pin RIMMs.
• Figure shows the two most common physical packages for memory used in recent systems. The top module is a 168-pin PC133 SDRAM DIMM. The bottom module is a 184-pin PC2100 DDR-SDRAM DIMM (faster DDR-SDRAM modules use the same package). The physical dimensions of both are the same: 5.375 inches (13.6525 cm) wide by 1.375 inches (3.4925 cm) tall. The width is standardized for all memory modules to ensure they fit the standard slot. The height may vary slightly, and is a factor only in that tall modules may interfere with other components in a tightly packed system. Both of these modules use nine chips, which indicates that they are Error Checking and Correction (ECC) modules. Nonparity modules use only eight chips.
PC133 SDRAM DIMM (top) and PC2100DDR-SDRAM DIMM
• The major difference between these DIMMs, other than the number of pins, is the location of the keying notches. SDRAM DIMMs use two notches, one centered and one offset. DDR-SDRAM DIMMs use only one offset keying notch. The number and position of these keying notches ensure that only the proper memory type can be installed in a slot and that the module is oriented correctly. Rambus RIMMs use similar physical packaging, but with the keying notches in different locations. Rambus RIMMs also cover the individual chips with a metal shroud designed to dissipate heat.
Characteristics of Memory• Memory, also known as RAM (Random Access Memory), provides a place for your PC to store information before writing / reading it to the hard drive. Its other use is to allow programs to run simultaneously without slowing your PC speed. Memory is also one of the cheapest ways to upgrade your computers speed so if you ever need to find out what memory setup you have or how good another setup is, you should know the key memory characteristics and what they mean.
• DDR – DDR, DDR2 and DDR3 stand for Double Data Rate. They are the measurement at which your memory transfers data chunks in a clock cycle. All memories work in clock cycles to synchronize their processes and a DDR unit transfers 2 data chunks per cycle. This means that a DDR memory will transfer twice as much data as an old memory unit would running the same length of clock cycle. Old memory units were SDRAM memories, which are not available for PCs anymore. The differences between DDR, DDR2 and DDR3 are their respective generations; the 3rd generation of DDR memory has a higher rate value than a DDR 1st generation.• Memory Clock Speed – The memory clock speed of computer memory is written in MHz. This is the value that determines how quickly the computer can transfer the memory on your PC. The total value that your memory can achieve is usually written after the DDR, DDR2 or DDR3 value. For example, DDR2-667 would represent 667 MHz. However, it is important to understand that the standard clock speed of the memory is always half of what is advertised; in this case, 333 MHz. This is because the DDR always runs at double the speed of what an old memory unit would have. Writing a DDR MHz value is the standard advertising values for memory chips.
• Memory Megabytes – Memory is measured in Megabytes, written as Mb. Standard practice for advertising memory units is to present it as a PC number with the Mb value written afterwards; for example PC6400. The MB value (6400) represents how much data is transferred per second and the higher the Mb value the more data that can be transferred. The Mb value is usually calculated by using the memorys clock frequency (MHz) and multiplying it by 8. This, however, is not always the exact number because manufacturers avoid selling memory with complicated numbers (e.g. 1066 MHZ x 8 = P8528) and instead round it up or down, in this case PC8500.