SIMMs / SDRAM DIMMs/ RIMMS/DDR (DOUBLE DATA RATE) SDRAM/COMPACT FLASH CARDS/ SMART MEDIA CARDS.
SIMMs is either 30 pin or 72 pin.. DIMMs are almost always 168pin but can either be 5 volts or 3.3 Volts un buffered..RIMMs require different slot and use a higher-speed memory bus than today’s DIMMs. DDR DIMMS are 184 pin and will not fit in a SDRAM socket. Compact flash and Smart media cards are used in digital cameras and PDA’s.
EDO or Non-EDO/FPM/SDRAM/DDR SDRAM:
EDO SIMMs will work only in Pentium systems. Fast Page Mode (FPM) SIMMs in all 486/586 and Pentium systems. SDRAM DIMMS are used in newer generation machines with Celeron, P-II, P-III, PIV and AMD K-6,K-6-2 ,Athlon, Duron, Thunderbird. CPUs. DDR DIMMS currently work only in a handful of high end systems.
Parity/ECC or Non-parity?
Parity/ECC (Error Checking Code) is a way to check the integrity of data and correct errors .Most of the new high end PCs and Servers use SDRAM with ECC, which are recommended for speed, stability and to ensure data integrity.
How many SIMMs/DIMMs at a time?
Unlike simms which had to arranged in 4 banks(30pin) or 2 banks (72pin) . SDRAM and DDR DIMMs have 64-bit access and can be installed one at a time and different capacities can be mixed.
What is SDRAM? What motherboards can support SDRAM?
Synchronous DRAMSDRAM are 168pin DIMM 3.3v unbuffered.. All SDRAM operations and signals are synchronized to the system clock i.e. runs at the same speed as the processor bus and carries signal only on the rising edge of the signal.. Motherboards with Intel BX, 820, 810e, 815,Via, Apollo chip set support SDRAM DIMM
What is DDR: How does it work?
Double data rate(DDR) SDRAM gives you twice the bandwidth of standard SDRAM. DDR DIMM is tied to front side bus clock in your system. The memory and bus execute instructions at the same time simultaneously. The big difference between DDR SDRAM and standard SDRAM is that DDR reads data on both rising and falling edges of a clock signal. This allows DDR module to transfer data twice as fast as SDRAM. For example instead of data rate of 133MHz, DDR memory transfers data at 266 MHz.
What is SPD (Serial Presence Detect)? How does it help?
SPD is an 8 pin serial device that stores critical parameter information including memory type, speed, size, voltage interface, number of row & column addresses and other critical information. Most of the motherboards require SPD for optimal performance.
What is the difference between high density and low density 64MB SDRAM modules?
Some older motherboards using the VX/TX chipsets recognize high density 64MB DIMMs as 16MB. You need to buy the older 64MB(66Mhz) DIMMs made out of low density chips which are rarely available or to buy two low density 32MB DIMMs
What are PC100 and PC133, PC143, PC 150?
PC100 is the specification issued by Intel for SDRAM DIMMs used on systems with a 100mhz bus. PC133 (CAS 2 latency) is the emerging next generation memory chip running at 133 MHz. All SDRAMs are theoretically downward compatible. However a 133MHz chip may not always work in a 100MHz bus machines. It is advisable to use memory of same bus speeds at a all times to prevent locking up or crashing of machines. DRAM performance is measured with two metrics: bandwidth and latency. PC-133 memory delivers the highest performance in both areas.
What is CAS latency?
Latency is the time it takes for the memory devices, after getting a command and address to produce its first data word. CAS latency is the clock cycles between the issuance of the read command and when the data comes out. This is a critical element of speed for PC100/133 memory. DIMMs with CAS latency 2 are faster than DIMMs with CAS latency 3. An 8ns DIMM with CAS latency 2 is faster than a 6ns DIMM with CAS latency 3. A 100 MHz DIMM operating at CAS latency 2 operates at 125 MHz enhancing system performance. A CAS 2 DIMM operates at 15-25% faster depending on system application. It is recommended that P-II & P-III and Athlon chips use CAS 2 DIMMS running at 100 or 133MHZ for extra speed, and crash free operation. CAS 2 DIMMs is an important component in systems where a user is “OVER CLOCKING ” the CPU. The logic board and SPD on CAS 2 DIMM are different than a regular PC-100 CAS 3 latency module. Buy PC133 SDRAMs because they are backward compatible and will work with the existing 100MHz bus as well as the 133MHz bus of the future making the investment worthwhile.
WHEN YOU BUY SDRAM DIMMs: Be careful because “NOT ALL SDRAMS ARE SAME”
Even though the manufacturer of the chip is the foremost factor when you buy a SDRAM there are other factors to be considered.
1) Ensure that you are not buying remanufactured/generic offbrand modules, which are usually sold at very low prices.
2) Buy SDRAM DIMMs made on 8 layer boards with SPD for optimal and stable performance. 3) Buy SDRAM with the right clock cycle and CAS latency. 4) Make sure the DIMMS can be overclocked 5) DIMMS should be downward compatible.
What can go wrong with cheaper, off spec, remarked SDRAM DIMMs.
1) Systems will frequently crash. 2) Will result in data errors corrupting the hard drive forcing you to re-install and re-configure your operating system and thereby reloading the entire data. 3) Automatic rebooting of the system throwing you off the programs you are working on and resulting in blank blue screens. 4) System shut downs after few hours of operation due to overheating of chips.
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