Random Access Memory or RAM is the component that stores temporary working data in the form of readable and rewritable computer memory.
It allows for quick access to the data, regardless of its physical location inside the memory.
The speed at which the processor can read and write data to the RAM is significantly faster when compared to direct - access data storage devices such as hard disk drives, CD-RWs, DVD RWs, Flash drives etc.
RAM is one of the two types of primary memory, the other being Read-Only Memory (ROM).
ROM can be identified as a game cartridge for consoles back in the day. Today, it can either be in the form of Digital Cameras, MP3 players, Modems or Solid-state and Flash Drives.
RAM is a volatile memory which requires power supply to retain data. When you turn off your PC, the RAM data is lost.
It is further divided into two types, namely, the Dynamic Random Access Memory (DRAM) and Static Random Access Memory (SRAM).
- DRAM stores and retains memory data by using capacitors. These capacitors lose charge over time due to leakage, even if the supply voltage is maintained. DRAMs are typically used for computer memory modules.
- SRAM uses transistors instead of capacitors in a cross-coupled flip–flop configuration and does not have leakage. It still requires constant power to maintain the state of charge. SRAMs are designed for processor caching.
Today, most operating systems require at about 1GB RAM for runing the system, which means that the system should have atleast 4GB or more of system RAM. Typical systems commonly have 8-16 GB RAM.
The amount of RAM in the system is very critical, even to basic users. Having more RAM enables the system to run more applications simultaneously.
If the system has less ram than required, then it will start using the secondary storage device like hard disks for paging or swap memory which is much slower than ram and will make the system feel very laggy.
RAM TECHNICAL SPECIFICATIONS
When you buy a RAM through online retailers, you get a long and detailed name of the item like this:
G.SKILL 32GB (2x16GB) Ripjaws V Series DDR4 PC4-25600 3200 MHz for Intel Z170 Platform Desktop Memory Model F4-3200C16D-32GVK
It usually starts with the item’s Brand name 'G.Skill', followed by the capacity and the number of modules '32 GB (2 x 16 GB)'. Then, the item series 'Ripjaws V'. Next are the bandwidth interface, max theoretical transfer speeds and memory clock speeds 'DDR4 PC4 – 25600 3200MHz'.
The less important details such as platform support and item code of the brand are usually at the end or in the product description. Having these technical specs on the name and understanding it makes it easier for the buyer to identify the particular RAM you need.
A RAM’s performance may vary depending on a very few specific factors which include Double Data Rate (DDR) classification, Frequency, CAS Latency, Memory Bandwidth, Memory Channels, and some others.
- Memory Size
- DDR Classification - The Type
- CAS Latency
- Memory Bandwidth
- Overclocking Support
- Heat Spreader/Sink
- RGB Support
1. Memory Size
This is the first and most basic thing to consider about the RAM that you plan to purchase. RAM sticks come in various sizes starting from 512 MB (half GB) to all the way upto 32GB or more in a single stick.
The motherboard determines the maximum amount of RAM that can be installed on it. So based on the number of slots and the maximum supported memory you need to choose RAM modules accordingly.
Most modern motherboards from MSI, Gigabyte, ASUS and ASRock support upto 128GB RAM in 4 slots. E-ATX motherboards with upto 8 slots can support 256 GB RAM.
Older motherboards supported upto 64 GB or less RAM.
A high-end desktop can go as high as 512GB and a further 2 TB for Server Workstations as the motherboards have dual sockets for dual-processor setups.
Depending upon the amount of RAM you wish to install, you also have to choose the number of modules to use. For instance if you want 32 GB Ram you can install a single 32 GB stick or 2x16GB sticks.
Usually dual memory modules in dual channels is slightly faster than a single memory module. In certain hardware setups where the gpu is using the system ram having dual channel ram can allow parallel access.
2. Double Data Rate Classification
Double Data Rate is the utilization of both the Rising and Falling edges of the clock signal. Using both edges of clock per data transfer cycle effectively makes it double the speed of the memory.
Each Generation of DDR improves the transfer rate (measured in MT/s - million transfers per second) and prefetch buffer and reduces power usage compared to the previous generation.
- Bus Clock (MHz) - 100 – 166
- Data Rate (MT/s) - 100 – 166
- Voltage (V) - 3.3
- Prefetch - 1n
DDR / DDR1
- Bus Clock (MHz) - 133 – 200
- Data Rate (MT/s) - 266 – 400
- Voltage (V) - 2.6
- Prefetch - 2n
- Bus Clock (MHz) - 266 – 400
- Data Rate (MT/s) - 533 – 800
- Voltage (V) - 1.8
- Prefetch - 4n
- Bus Clock (MHz) - 533 – 800
- Data Rate (MT/s) - 1066 – 1600
- Voltage (V) - 1.5
- Prefetch - 8n
- Bus Clock (MHz) - 1066 – 1600
- Data Rate (MT/s) - 2133 – 3200
- Voltage (V) - 1.2
- Prefetch - 8n
Note that most RAMs would mention a clock speed like 3200 Mhz which is not totally correct. DDR or Double Data Rate means 2 transfers per clock cycle which means that if the base clock speed is 1600 Mhz the effective transfer speed is twice of that, hence 3200 Mhz.
The correct unit for measuring speed is MT/s or Mega Transfers/s. In the context of RAM speed, it is sometimes equivalent to Mhz and both the terms can be used interchangeably.
When choosing RAM for your PC build you are mostly limited to whatever the motherboard can take in. If the motherboard has a DDR4 slot, you need DDR4 RAM and the same with DDR3 or DDR2.
DDR2 and DDR3 are however largely obsolete now, except for stocks of old motherboards models that might be having them.
Most current motherboards are DDR4 based and DDR5 is the next upcoming RAM standard.
Reading the Specs
Most RAM modules have something like PC3 or PC4 written on them. PC3 indicates DDR3 and PC4 indicates DDR4
Take the following name for example:
Hynix 4GB 1Rx8 PC3-12800U DDR3-1600MHz desktop 240-Pin DIMM RAM Memory Module
The specs can be broken down as follows: PC3 means DDR3 and 12800 is the max bandwidth. Dividing it by 8 gives the effective i/o clock speed which is 1600 Mhz. The "U" indicates un-buffered or non-ECC
Another example with ECC support is like this:
Hynix 4GB 2Rx8 PC3 10600E DDR3 1333MHz ECC Memory Module
The "E" indicates ECC support.
If its a laptop RAM module then the letter "S" will be present next to the bandwidth number like this:
Hynix 4GB 2Rx8 PC3-12800S DDR3-1600MHz
The "S" stands for SO-DIMM or Small Outline DIMM.
The Rx8 indicates the Rank of the RAM.
1Rx8 means the memory chips are on one side of the RAM module and 2Rx8 means the memory chips are on both sides of the RAM module.
3. Frequency - Clock Speed
RAM frequency or clock speed is the maximum number of commands it can handle per second, measured in the unit of Megahertz (MHz) or MT/s.
Ideally, you want to have the highest possible frequency that your motherboard can support. Typical DDR4 speeds as mentioned by various brands are:
- DDR4-2400 2400 MT/s
- DDR4-2666 2666 MT/s
- DDR4-3200 3200 MT/s
- DDR4-4133 4133 MT/s
- DDR4-4266 4266 MT/s
There are many more values other than the ones mentioned above.
Note that the frequency is mentioned in MT/s which is million transfer per second. With RAM, the overall MT/s speed is equivalent to Mhz, hence they are often used interchangeably.
For example the IO Bus Clock speed of DDR4-3200 RAM is actually 1600 Mhz. However since DDR memory makes 2 transfers per cycle, the effective speed is equivalent to 3200 Mhz which is also mentioned as 3200 MT/s.
In general higher frequencies are better, but the performance boost will also depend on the processor and motherboard support.
Although Intel Processors feature the XMP2.0 technology that allows the RAM frequencies to be boosted and overclocked to higher speeds with a simple change in profile, it does not get a significant boost in the overall performance like AMD’s Ryzen Processor does.
Due to the architectural design of Ryzen’s Infinity Fabric, higher RAM frequencies result in better performance scaling.
Today, the most common DDR4 RAMs start from 2133 MHz to as high as 4000 MHz with capacities ranging from 4 GB to 32 GB per module and a total of 128 GB for consumer-level systems. With overclocking the RAM frequency can be boosted upto 4800 Mhz or even higher in extreme setups.
Keep in mind that higher frequency RAM is also more expensive, so you may want to consider the price to performance ratio based on your needs. If your machine needs to do a lot of high speed processing, then high speed RAM might be beneficial. But for general usage the benefits of higher frequency may be negligible to notice.
4. CAS Latency
Column Address Strobe (CAS) Latency or CL is the amount of time between sending a READ command to the RAM and the time when the data is available. It is measured in absolute time in nano-seconds (ns) as well has clock cycles.
RAM sticks will often mention the CAS latency values in their specifications and they look something like this:
It is usually the first number that indicates the CAS latency. Here it is 16 for example and it is the number of clock cycles required for 1 read operation to complete. The rest of the 4 numbers indicate other metrics including, RAS to CAS Delay, RAS Precharge, Active to Precharge Delay and Command Rate.
Usually newer DDR technologies have higher CAS latency values, but since the frequency is higher, each clock cycle is of s shorter duration, make it faster overall.
DDR3 RAM modules have a latency value of around 7 to 11 while DDR4 RAMs go as high as 15 to 18.
For more information on CAS Latency check the wikipedia article:
Usually when purchasing new RAM sticks for a PC, it is not very important to consider the latency values, since most modern ram modules have pretty fast operation times.
However if you are looking for the best speeds at all levels for a production or workstation machine then look for RAM modules with lower values of CAS latency.
5. Memory Bandwidth
The rate at which a RAM can read or write data to/from the processor and vice versa is termed as the Memory Bandwidth. The memory bandwidth is determined by the memory bus width, the clock speed and transfers per cycle.
Normally, the advertised Memory Bandwidth of a particular RAM is the maximum theoretical bandwidth and not the sustained operating bandwidth of the memory.
For example a DDR4 RAM that mentions speed of 3200 Mhz will have a bandwidth of around 8x of that number which is equal to 3200 x 8 = 25600 MB/s
25600 MB/s is the peak bandwidth if the memory bus width is actually 8 bytes or 64 bits.
Although DDR4 has dramatically improved the theoretical and actual transfer rate of data from the RAM to the Processor, there is still a physical limitation.
Here are some more typical values of the memory bandwidth and frequencies:
- Bus Clock Speed: 800 Data Rate: 1600 MT/s Bandwidth (Max): 12800 MB/s
- Bus Clock Speed: 1200 Data Rate MT/s: 2400 Bandwidth (Max): 19200 MB/s
More details about transfer rates and supported bandwidth of DDR4 specifications can be found at the wikipedia page:https://en.wikipedia.org/wiki/DDR4_SDRAM
Check Motherboard Support
If you are building a new PC then its generally advisable to go with the highest possible RAM speed and bandwidth that your motherboard can support.
3200 Mhz / 25600 MB/s is quite popular presently.
Your motherboard specifications will mention the maximum amount of RAM memory and frequency that it can support. So your RAM should be within the stated limits or lower.
For instance if the motherboard supports only upto 2666MHz then ideally you should purchase RAM with transfer rate within that number.
Theoretically if you add a high frequency RAM on a motherboard with lower frequency, the RAM would still work but at the lower frequency. However it is not guaranteed to work like that. If it doesn't you have no other option except to replace it with a compatible memory module.
Carefully check the bandwidth number like 19200, 12800, 25600 and divide it by 8 to get the transfer rate frequency and that number should be compatible with whatever your motherboard supports.
6. Memory Channels
The memory channels are the link between the RAM and the CPU. It is the electrical path for data to move back and forth.
Most modern consumer-grade or high-end motherboards employ two or four rows of memory channel configuration to take advantage of multi-channel memory technology.
Utilizing multiple channels such as Dual, Triple and Quad Channel, in theory, multiplies the rate of data transfer (bandwidth) by the number of channels active.
The advantage of running Dual or Quad channel memory configuration with lower capacity RAMs is that it will provide the same capacity as a larger stick of memory while at the same time doubling and quadrupling the amount of memory bandwidth.
Although advantageous, Dual and Quad channel memory configuration have certain limitations. For it to work, the RAM modules must be a matched pair of the same specifications to each other, and it needs to be installed in the matching bank.
When installing multiple ram modules, it is necessary to ensure that they are as identical as possible to get the best performance from both channels.
RAM memory is often available in "kits" of 2 sticks to ensure that the memory modules match in capacity, speed, latency, number of chips and sides, and the size of rows and columns.
This way you get exactly identical memory modules for best performance.
Modules of different speed will be run in Dual-channel mode but at the speed of the slowest module.
Here is an article on Crucial's website that explains dual channel memory:https://www.crucial.com/articles/about-memory/what-is-dual-channel-memory
7. ECC Vs NON–ECC Memory
In the consumer space, memory modules are in the form factor of DIMM (Dual In-Line Memory Module) for desktop PCs and SO-DIMM (Small Outline DIMM) for Laptop PCs.
These two form factors are the Unbuffered types of Memory.
Buffered Memory or Error Correction Code (ECC) Memory has an additional register between the Memory Controller and the DRAM. This reduces the electrical load on the memory controller, which then allows a singular system to be stable without using multiple modules.
The advantage of having an extra chip (register) is the ability to auto-detect and correct memory errors, thus preventing data corruption. It also protects against crashes and data loss during power outages or surges.
On the other hand, Unbuffered Memory or Non-ECC memory has no register between the DRAM and memory controller. As a result, it has direct access to the controller which makes data transfer, bandwidth and overall operation faster in exchange for having no data loss protection.
ECC today is rapidly being adapted to Enthusiasts/High-Performance desktop and Professional consumer level. It was previously only available to enterprise workstations, server grade motherboards, data banks.
Checking your RAM for ECC support
If you wish to check whether your RAM has ECC support or not, there are a couple of ways to do so.
You can find ECC support information inside BIOS. Different motherboard bios systems have different formats, so you need to find it out based on your exact motherboard model.
On Ubuntu you can use the dmidecode command and check the output for Error Correction information
$ sudo dmidecode -t memory # dmidecode 3.2 Getting SMBIOS data from sysfs. SMBIOS 3.0.0 present. Handle 0x003D, DMI type 16, 23 bytes Physical Memory Array Location: System Board Or Motherboard Use: System Memory Error Correction Type: None Maximum Capacity: 64 GB Error Information Handle: Not Provided Number Of Devices: 4 Handle 0x003E, DMI type 17, 40 bytes
Alternatively you can use the memtest86 tool from https://www.memtest86.com/.
It runs a lot of tests on your RAM and checks the overall health.
8. Heat Spreader / Sink
Modern RAM have large memory capacities and run at faster frequencies. As a result they product significant amount of heat that needs to be dissipated for optimal performance and longevity of the hardware.
Modern RAM modules have enclosures containg heat spreaders or passive heat sinks which help keep the memory chips cooler. You can see them on RAM from all major brands including Corsair, Crucial, G.Skill, Kingston etc.
Heat spreaders for RAMs are usually made of Aluminum, to efficiently dissipate heat and maintain high clock speeds.
High frequency or overclocking RAMs tend to have taller heat sinks while low profile RAMs that operate at lower frequencies have shorter heat sinks.
Larger heat spreaders might bump into the air cooler of the cpu if the air cooler is large and wide. Check the amount of clearance space beside the air cooler to decide how big the RAM dimension can be.
RGB is a fancy addon to the aesthetics of the RAM sticks. If you like the the glowing LEDs then go ahead and select RAMs with inbuilt RGB.
However note that sometimes, the air coolers are so large that they overshadow the visibility of the RAM sticks making the RGB effects completely hidden. In such a case spending extra money for RGB RAM may be totally useless.
So if you plan to install RGB ram in your system, first make sure that, the RAM is going to be clearly visible from the pc case.
If you are looking to buy new RAM modules for your existing or new PC, the most important things to check are the size and frequency. The frequency should be compatible with your motherboard and should be the highest possible.
If you have any questions or suggestions let us know in the comments below.
Links and Resourceshttps://en.wikipedia.org/wiki/Memory_rank