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Annabell · 07-07-07, 08:02 AM

Random access memory (usually known by its acronym, RAM)

Timings
When you buy some memory (RAM) on line or from a store on the packaging or in the spec you will see numbers "4.5-4-4-12" or "4-4-4-12" what do they mean? Or have you seen words like "CAS" and "tRCD"? These are the timings for the memory or the speed at which it processes certain commands. This whole settings area can be quite confusing and you need a certain knowledge of it, if you plan on overclocking, but some of you may just like to know what they are.
CAS (tCL) Timing CAS stands for Column Address Strobe or Column Address Select. It controls the amount of time in cycles between sending a reading command and the time to act on it. From the beginning of the CAS to the end of the CAS is the latency. The lower the time of these in cycles, the higher the memory performance.
e.g.: 4.5-4-4-12 The bold "4.5" is the CAS timing.

tRCD Timing RAS to CAS Delay (Row Address Strobe/Select to Column Address Strobe/Select). Is the amount of time in cycles for issuing an active command and the read/write commands.
e.g.: 4.5-4-4-12 The bold "4" is the tRCD timing.
tRP Timing Row Precharge Time. This is the minimum time between active commands and the read/writes of the next bank on the memory module
e.g.: 4.5-4-4-12 The bold "4" is the tRP timing.

tRAS Timing Min RAS Active Time. The amount of time between a row being activated by precharge and deactivated. A row cannot be deactivated until tRAS has completed. The lower this is, the faster the performance, but if it is set too low, it can cause data corruption by deactivating the row too soon.
tRAS = tCL + tRCD + tRP (+/- 1) so that it gives everything enough time before closing the bank,
e.g.: 4.5-4-4-12 The bold "12" is the tRAS timing.
These are the four timings that you would see when memory is being rated. It is in the order of CAS-tRCD-tRP-tRAS.
(The 4.5-4-4-12 figure is just an example for memory timings.) my memory in my main Computer is Corsair 2GB DDR2 XMS2 TwinX (2x1GB matched pair), memory timings 4-4-4-12.

Certain memories can take tighter (lower) timings at higher speeds. These are the more expensive Memory / Ram out of the bunch. There are also other timings to consider in your BIOS. Not all Motherboards will have options like these, and some Motherboards list there timings in a different configuration "eg" CAS-tRCD-tRAS-tRP. Also not many memory modules have the .5 but some are still made
CL stands for CAS (column address strobe) latency, which is the number of clock cycles it takes before data starts to flow after a command is received. Low CAS latency at a given frequency is faster than high CAS latency at that same frequency. (For example, CAS2 is
faster than CAS3.) However, lower CAS latency will NOT necessarily make your system faster. Your computer will only run as fast as the "slowest link" in your system, so you can't speed up your computer by adding memory that is faster than your current memory. The way to make your system faster is to add more megabytes (MB) of memory.
Memory speeds are written in different formats depending on the type of memory technology your computer uses. FPM and EDO speeds are written in nanoseconds (ns). SDRAM, DDR, and DDR2 speeds are written in megahertz (MHz) or with a "PC" rating.

The memory access time of your computer decides how fast the system can read from or write to its random access memory (RAM). The shorter the access time, the faster is the system able to carry out its instructions - resulting in better performance and less "lag". Most modern RAM modules are capable of very short memory access times, hence producing very high memory bandwidth (for example, a DDR2 RAM module is theoretically capable of 6.400 GB/s bandwidth).
Memory Types

EDO RAM
Extended Data Out RAM is a type of dynamic random access memory that allows a new access cycle to be started while the data of the previous cycle has not yet been accessed by the CPU. It offers improvement over the earlier Fast Page Module RAM as it eliminates wait states by keeping the output buffer active until the next cycle began. EDO RAM is subsequently superceded by SDRAM
SDRAM
SDRAM stands for Synchronous RAM (Dynamic Random Access Memory). It is a solid state computer memory that waits for the rising or falling edge of the clock signal to synchronize data transfer (see diagram below). SDRAM DIMMs are rated according to its maximum clock rate and they transfer 8 bytes per clock cycle. They are available in 168-pin DIMM module (used in desktop computers) and 144-pin SODIMM nodule (used in most laptops and embedded hardware devices). Physically, a 168-pin DIMM SDRAM has 2 "notches" (as opposed to 1 on a 184-pin DIMM DDR RAM).
DDR RAM
DDR RAM stands for double data rate RAM. It achieves greater bandwidth that the SDRAM because data exchange synchronization with the CPU is achieved at the rising and falling edge of the clock signal (see diagram below). Thus a DDR RAM has double the bandwidth of an equivalent SDRAM operating at the same bus speed. DDR RAM DIMM modules have 184-pin and one notch.
DDR2 RAM
The advantage of DDR2 RAM over DDR RAM is its ability for much higher clock speed and that DDR2 has a doubled bus frequency for the same physical clock rate, so doubling the effective data rate another time. Hence, a DDR2 RAM module rated at 100MHz will have an I/O clock of 200MHz. DDR2 RAM DIMM module has 240 pins and is not backward compatible with DDR DIMMs.

Here's a rough guide to relative memory speeds below

Your Computer
In general, you should match the speed and type of memory technology that is already in your system common types of memory technology today include DDR2 (double data rate, second generation) SDRAM and DDR (double data rate, first generation) SDRAM. Many older systems use SDR (single data rate) SDRAM, fast page mode (FPM), or extended data out (EDO). Each of these memory types comes in a variety of speeds. And while most systems will accept only one type of memory technology (the very few motherboards that can accept more than one type of memory will only allow you to use one type at a time), if you try to mix the speed of the memory in a system. Just keep in mind that your computer is made to handle a specific memory speed, so even if you add a faster speed memory, your computer will only allow it to run at the speed your computer was made to handle.
Installing RAM

First turn off the mains power supply but leave the power cable plugged in as to connect earth, most PSUs "Power supply units" have a ON/OFF switch at the back of the Computer set this to OFF now press the START button on your Computer this will drain any power within the system to LEDs / Fans, and access your Motherboard.
Unpack the RAM Make sure at this stage that you have your anti-static measures in place and even briefly make contact with both hands on the metal of the case to make sure. All of todays RAM installation the procedure is exactly the same. Note, however, that SIMMs must be installed in pairs.
The RAM module should be held at its edges and note the notches along the bottom edge these need to line up with the Ram slot architecture "so the Ram can only be installed one way" as with the CPU's and Adapter cards, Ram modules have a 'keying' system. Check with the Motherboard manual to find the first slot on some Motherboards the slots are visibly numbered (usually slot 0) and fill the slots in numerical order as appropriate.
RAM module insertion is a simple case of pushing the small white"sometimes black" retaining clips slightly out wards, then inserting the RAM module (with aligned key positions) into the slot with a gentle pressure with your fingers at the top edge of the RAM module. You will know when it is fully inserted as the retaining clips will automatically move into position and secure the RAM you can also feel the RAM click in.
Upon completion of installing your new RAM and you have your Computer side panel / casing in place boot / start up your Computer and note the RAM count on your boot screen "on some systems this only flashes on for a second or so but you can check that your OS "operating system" is seeing / recognizing the new RAM via your BIOS or in Windows click Start > Settings > Control Panel > System, at the bottom of the System Window you will see the amount of RAM your Computer is seeing.
Most of todays Operating Systems will run well on 1GB of RAM but if using RAM hungry applications 2GB would be better. Note RAM amounts are only my suggestion.

Please see pictures below-

Motherboard with Yellow / Black RAM slots at top right

RAM module Note key notches along bottom edge

Ann.

dhallstar · 15-08-07, 07:43 PM

Thank You for the informative post on RAM.

phillipg10 · 07-12-07, 08:24 PM

Very good post also would like to add somthing about RAM.

you may see people or you may have 1gb or 3gb RAM in your PC this will bottleneck your ram to only 64bits using Dual channel increases this to 128bits

Also when buying RAM its always better to have identical Modules using different modules of RAM can cause instabillity and somtimes the PC will not even POST (Power on self test) which in over words means will not boot into windows.

yatik · 23-01-08, 10:54 PM

Thanks, that was very helpful info.

jegitoe · 21-04-08, 04:22 PM

Thanks for the info.... Updating comp atm nice to have some know how ^^...

phil67 · 09-05-08, 11:05 PM

ok you clever people out there ! Q 1 got a doggle ! from 3 network today for my birthday hey happy birthday !! pluged it into my laptop NOTHING? i think it should light up green ?? Q2 If i do get this working plan to use it in usa 3 network want £3 a mega bite ! fine doesanyone know how much time chatting say on skype that would give me? or emails or big macs even?

zd_brink · 04-06-08, 01:47 PM

i am pretty sure i may be in the wrong thread here, but just wanted to ask a quick question about my mac. i have an old mac mini (the old ppc version). it has a 512MB pc333 hynix ram in it. i was wondering if a 1GB pc400 module would work on it... thanks.

aldouk · 06-06-08, 11:31 PM

Quote:

Originally Posted by zd_brink

i am pretty sure i may be in the wrong thread here, but just wanted to ask a quick question about my mac. i have an old mac mini (the old ppc version). it has a 512MB pc333 hynix ram in it. i was wondering if a 1GB pc400 module would work on it... thanks.

To answer your question, yes PC400 modules should work with a pc333 system bus but it will run at the slower speed. Be aware that it could also cause you some issues if you try to use pc333 memory and pc400 memory at the same time.

Cheers

Al

07-07-07, 08:02 AM	#1 (permalink)
Annabell Computing Moderator Join Date: May 2007 Location: UK Posts: 1,667 Thanks: 0 Thanked 9 Times in 9 Posts	PC Ram Random access memory (usually known by its acronym, RAM) Timings When you buy some memory (RAM) on line or from a store on the packaging or in the spec you will see numbers "4.5-4-4-12" or "4-4-4-12" what do they mean? Or have you seen words like "CAS" and "tRCD"? These are the timings for the memory or the speed at which it processes certain commands. This whole settings area can be quite confusing and you need a certain knowledge of it, if you plan on overclocking, but some of you may just like to know what they are. CAS (tCL) Timing CAS stands for Column Address Strobe or Column Address Select. It controls the amount of time in cycles between sending a reading command and the time to act on it. From the beginning of the CAS to the end of the CAS is the latency. The lower the time of these in cycles, the higher the memory performance. e.g.: 4.5-4-4-12 The bold "4.5" is the CAS timing. tRCD Timing RAS to CAS Delay (Row Address Strobe/Select to Column Address Strobe/Select). Is the amount of time in cycles for issuing an active command and the read/write commands. e.g.: 4.5-4-4-12 The bold "4" is the tRCD timing. tRP Timing Row Precharge Time. This is the minimum time between active commands and the read/writes of the next bank on the memory module e.g.: 4.5-4-4-12 The bold "4" is the tRP timing. tRAS Timing Min RAS Active Time. The amount of time between a row being activated by precharge and deactivated. A row cannot be deactivated until tRAS has completed. The lower this is, the faster the performance, but if it is set too low, it can cause data corruption by deactivating the row too soon. tRAS = tCL + tRCD + tRP (+/- 1) so that it gives everything enough time before closing the bank, e.g.: 4.5-4-4-12 The bold "12" is the tRAS timing. These are the four timings that you would see when memory is being rated. It is in the order of CAS-tRCD-tRP-tRAS. (The 4.5-4-4-12 figure is just an example for memory timings.) my memory in my main Computer is Corsair 2GB DDR2 XMS2 TwinX (2x1GB matched pair), memory timings 4-4-4-12. Certain memories can take tighter (lower) timings at higher speeds. These are the more expensive Memory / Ram out of the bunch. There are also other timings to consider in your BIOS. Not all Motherboards will have options like these, and some Motherboards list there timings in a different configuration "eg" CAS-tRCD-tRAS-tRP. Also not many memory modules have the .5 but some are still made CL stands for CAS (column address strobe) latency, which is the number of clock cycles it takes before data starts to flow after a command is received. Low CAS latency at a given frequency is faster than high CAS latency at that same frequency. (For example, CAS2 is faster than CAS3.) However, lower CAS latency will NOT necessarily make your system faster. Your computer will only run as fast as the "slowest link" in your system, so you can't speed up your computer by adding memory that is faster than your current memory. The way to make your system faster is to add more megabytes (MB) of memory. Memory speeds are written in different formats depending on the type of memory technology your computer uses. FPM and EDO speeds are written in nanoseconds (ns). SDRAM, DDR, and DDR2 speeds are written in megahertz (MHz) or with a "PC" rating. The memory access time of your computer decides how fast the system can read from or write to its random access memory (RAM). The shorter the access time, the faster is the system able to carry out its instructions - resulting in better performance and less "lag". Most modern RAM modules are capable of very short memory access times, hence producing very high memory bandwidth (for example, a DDR2 RAM module is theoretically capable of 6.400 GB/s bandwidth). Memory Types EDO RAM Extended Data Out RAM is a type of dynamic random access memory that allows a new access cycle to be started while the data of the previous cycle has not yet been accessed by the CPU. It offers improvement over the earlier Fast Page Module RAM as it eliminates wait states by keeping the output buffer active until the next cycle began. EDO RAM is subsequently superceded by SDRAM SDRAM SDRAM stands for Synchronous RAM (Dynamic Random Access Memory). It is a solid state computer memory that waits for the rising or falling edge of the clock signal to synchronize data transfer (see diagram below). SDRAM DIMMs are rated according to its maximum clock rate and they transfer 8 bytes per clock cycle. They are available in 168-pin DIMM module (used in desktop computers) and 144-pin SODIMM nodule (used in most laptops and embedded hardware devices). Physically, a 168-pin DIMM SDRAM has 2 "notches" (as opposed to 1 on a 184-pin DIMM DDR RAM). DDR RAM DDR RAM stands for double data rate RAM. It achieves greater bandwidth that the SDRAM because data exchange synchronization with the CPU is achieved at the rising and falling edge of the clock signal (see diagram below). Thus a DDR RAM has double the bandwidth of an equivalent SDRAM operating at the same bus speed. DDR RAM DIMM modules have 184-pin and one notch. DDR2 RAM The advantage of DDR2 RAM over DDR RAM is its ability for much higher clock speed and that DDR2 has a doubled bus frequency for the same physical clock rate, so doubling the effective data rate another time. Hence, a DDR2 RAM module rated at 100MHz will have an I/O clock of 200MHz. DDR2 RAM DIMM module has 240 pins and is not backward compatible with DDR DIMMs. Here's a rough guide to relative memory speeds below Your Computer In general, you should match the speed and type of memory technology that is already in your system common types of memory technology today include DDR2 (double data rate, second generation) SDRAM and DDR (double data rate, first generation) SDRAM. Many older systems use SDR (single data rate) SDRAM, fast page mode (FPM), or extended data out (EDO). Each of these memory types comes in a variety of speeds. And while most systems will accept only one type of memory technology (the very few motherboards that can accept more than one type of memory will only allow you to use one type at a time), if you try to mix the speed of the memory in a system. Just keep in mind that your computer is made to handle a specific memory speed, so even if you add a faster speed memory, your computer will only allow it to run at the speed your computer was made to handle. Installing RAM First turn off the mains power supply but leave the power cable plugged in as to connect earth, most PSUs "Power supply units" have a ON/OFF switch at the back of the Computer set this to OFF now press the START button on your Computer this will drain any power within the system to LEDs / Fans, and access your Motherboard. Unpack the RAM Make sure at this stage that you have your anti-static measures in place and even briefly make contact with both hands on the metal of the case to make sure. All of todays RAM installation the procedure is exactly the same. Note, however, that SIMMs must be installed in pairs. The RAM module should be held at its edges and note the notches along the bottom edge these need to line up with the Ram slot architecture "so the Ram can only be installed one way" as with the CPU's and Adapter cards, Ram modules have a 'keying' system. Check with the Motherboard manual to find the first slot on some Motherboards the slots are visibly numbered (usually slot 0) and fill the slots in numerical order as appropriate. RAM module insertion is a simple case of pushing the small white"sometimes black" retaining clips slightly out wards, then inserting the RAM module (with aligned key positions) into the slot with a gentle pressure with your fingers at the top edge of the RAM module. You will know when it is fully inserted as the retaining clips will automatically move into position and secure the RAM you can also feel the RAM click in. Upon completion of installing your new RAM and you have your Computer side panel / casing in place boot / start up your Computer and note the RAM count on your boot screen "on some systems this only flashes on for a second or so but you can check that your OS "operating system" is seeing / recognizing the new RAM via your BIOS or in Windows click Start > Settings > Control Panel > System, at the bottom of the System Window you will see the amount of RAM your Computer is seeing. Most of todays Operating Systems will run well on 1GB of RAM but if using RAM hungry applications 2GB would be better. Note RAM amounts are only my suggestion. Please see pictures below- Motherboard with Yellow / Black RAM slots at top right RAM module Note key notches along bottom edge Ann. __________________ As tonight is my last night in England i will be here, coz love you all lots. Last edited by Annabell; 07-07-07 at 08:04 AM.

15-08-07, 07:43 PM	#2 (permalink)
dhallstar Junior Member Join Date: Aug 2007 Posts: 26 Thanks: 0 Thanked 0 Times in 0 Posts	Re: PC Ram Thank You for the informative post on RAM.

07-12-07, 08:24 PM	#3 (permalink)
phillipg10 Junior Member Join Date: Dec 2007 Posts: 7 Thanks: 0 Thanked 0 Times in 0 Posts	Re: PC Ram Very good post also would like to add somthing about RAM. you may see people or you may have 1gb or 3gb RAM in your PC this will bottleneck your ram to only 64bits using Dual channel increases this to 128bits Also when buying RAM its always better to have identical Modules using different modules of RAM can cause instabillity and somtimes the PC will not even POST (Power on self test) which in over words means will not boot into windows.

23-01-08, 10:54 PM	#4 (permalink)
yatik Technology Forums Join Date: Jan 2008 Posts: 46 Thanks: 0 Thanked 1 Time in 1 Post	Re: PC Ram Thanks, that was very helpful info.

21-04-08, 04:22 PM	#5 (permalink)
jegitoe Junior Member Join Date: Apr 2008 Location: Kent Posts: 8 Thanks: 1 Thanked 0 Times in 0 Posts	Re: PC Ram Thanks for the info.... Updating comp atm nice to have some know how ^^...


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09-05-08, 11:05 PM	#6 (permalink)
phil67 Junior Member Join Date: Apr 2008 Posts: 8 Thanks: 0 Thanked 1 Time in 1 Post	Re: PC Ram ok you clever people out there ! Q 1 got a doggle ! from 3 network today for my birthday hey happy birthday !! pluged it into my laptop NOTHING? i think it should light up green ?? Q2 If i do get this working plan to use it in usa 3 network want £3 a mega bite ! fine doesanyone know how much time chatting say on skype that would give me? or emails or big macs even?

04-06-08, 01:47 PM	#7 (permalink)
zd_brink Junior Member Join Date: Jun 2008 Posts: 14 Thanks: 0 Thanked 0 Times in 0 Posts	Re: PC Ram i am pretty sure i may be in the wrong thread here, but just wanted to ask a quick question about my mac. i have an old mac mini (the old ppc version). it has a 512MB pc333 hynix ram in it. i was wondering if a 1GB pc400 module would work on it... thanks.