Shopping for RAM can be confusing, though. What’s the difference between DDR3 and DDR4? DIMM and SO-DIMM? Is there a difference between DRR3-1600 and PC3-12800? Is RAM latency and timing important?
Read on for explanations on the different kinds of RAM, how to read RAM specifications, and exactly how RAM works.
What Is RAM?
RAM stands for Random Access Memory. It acts as a middle ground between the small, super-fast cache in your CPU and the large, super-slow storage of your hard drive or solid-state drive (SSD). Your system uses RAM to store working parts of the operating system temporarily and the data your applications are using actively. RAM is not a form of permanent storage.
Think of your computer as an office. The hard drive is the filing cabinet in the corner. The RAM is like an entire office workstation, while the CPU cache is like the actual working area where you actively work on a document.
The more RAM you have, the more things you can have quick access to at any one time. Just as having a bigger desk can hold more bits of paper on it without becoming messy and unwieldy (as well as requiring more trips back to the filing cabinet to reorganize).
Unlike an office desk, however, RAM cannot act as permanent storage. The contents of your system RAM are lost as soon as you turn the power off. Losing power is like wiping your desk clean of every document.
RAM Usually Means SDRAM
When people talk about RAM, they’re usually talking about Synchronous Dynamic RAM (SDRAM). SDRAM is what this article discusses, too. For most desktops and laptops, RAM appears as a stick that you can insert into the motherboard.
Unfortunately, there is a rising trend for super thin and light laptops to have the RAM soldered to the motherboard directly in the interest of saving space. However, this sacrifices upgradability and repairability.
Do not confuse SDRAM with SRAM, which stands for Static RAM. Static RAM is the memory used for CPU caches, among other things. It is much faster but also limited in its capacity, making it unsuitable as a replacement for SDRAM. It is highly unlikely you will encounter SRAM in general usage, so it is not something you should worry about.
The Form Factors of RAM
For the most part, RAM comes in two sizes: DIMM (Dual In-Line Memory Module), which is found in desktops and servers, and SO-DIMM (Small Outline DIMM), which is found in laptops and other small form factor computers.
Though the two RAM form factors use the same technology and functionally work in exactly the same way, you cannot mix them. You can’t just jam a DIMM stick into a SO-DIMM slot, and vice versa (the pins and slots don’t line up!).
When you are buying RAM, the first thing to figure out is its form factor. Nothing else matters if the stick won’t fit!
What Does DDR Mean?
The RAM you use in your computer operates using Double Data Rate (DDR). DDR RAM means that two transfers happen per clock cycle. Newer types of RAM are updated versions of the same technology, hence why RAM modules carry the label of DDR, DDR2, DDR3, and so on.
While all desktop RAM generations are the same physical size and shape, they aren’t compatible.
You cannot use DDR3 RAM in a motherboard that only supports DDR2. Likewise, DDR3 doesn’t fit in a DDR4 slot. To stop any confusion, each RAM generation has a notch cut in the pins at different locations. That means you cannot accidentally mix your RAM modules up or damage your motherboard, even if you buy the wrong type.
DDR2 is the oldest kind of RAM you’re likely to come across today. It has 240 pins (200 for SO-DIMM). DDR2 has been well and truly superseded, but you can still buy it in limited quantities to upgrade older machines. Otherwise, DDR2 is obsolete.
DDR3 was released way back in 2007. Although DDR4 officially superseded it in 2014, you will still find many systems using the older RAM standard. Why? Because it wasn’t until 2016 (two years after DDR4 launched) that DDR4 capable systems really picked up steam.
Furthermore, DDR3 RAM covers a huge range of CPU generations, stretching from Intel’s LGA1366 socket through to LGA1151, as well as AMD’s AM3/AM3+ and FM1/2/2+. For Intel, that covers the Intel Core i7 line introduction in 2008 through to the 7th generation Kaby Lake CPUs in 2016.
DDR3 RAM has the same number of pins as DDR2. However, it runs a lower voltage and has higher timings (more on RAM timings in a moment), so it isn’t compatible. Also, DDR3 SO-DIMMs have 204 pins versus DDR2’s 200 pins.
DDR4 hit the market in 2014 and took some time to become the most popular type of RAM, taking the top-spot from DDR3 sometime in 2017. Since then, DDR4 use has steadily grown to the point where it now accounts for around 80 percent of all RAM sales worldwide.
An initial period of high prices saw many users stick with the previous generation. However, as the latest Intel and AMD CPUs use DDR4 RAM exclusively, most users have switched to the new generation or will upgrade the next time they update their system hardware.
DDR4 drops the RAM voltage even further, from 1.5V to 1.2V, while increasing the number of pins to 288.
DDR5 was set to hit consumer markets in 2019. That didn’t happen. It didn’t really happen in 2020, either, as the new memory spec was only released in mid-2020. The result is that at the time of writing, DDR5 RAM is just starting to filter out into the world, but only by way of expensive showcase modules rather than consumer-grade products.
DDR5 will continue with a 288-pin design, although the RAM voltage will drop to 1.1V. DDR5 RAM performance is expected to double the fastest standard of the previous DDR4 generation. For example, SK Hynix revealed the technical details of a DDR5-6400 RAM module, the fastest possible allowed under the DDR5 standard.
But, as with any new computer hardware, expect an extremely high price at launch. Also, if you’re considering buying a new motherboard, don’t focus on DDR5. It isn’t available yet, and despite what SK Hynix says, it will take Intel and AMD a while to prepare
RAM Jargon: Speed, Latency, Timing, and More
You’ve wrapped your head around SDRAM, DIMMs, and DDR generations. But what about the other long strings of numbers in the RAM model? What do they mean? What is RAM measured in? And what about ECC and Swap?
Here are the other RAM specification terms you need to know.
Clock Speed, Transfers, Bandwidth
You may have seen RAM referred to by two sets of numbers, like DDR3-1600 and PC3-12800. These both reference and allude to the generation of the RAM and its transfer speed. The number after DDR/PC and before the hyphen refers to the generation: DDR2 is PC2, DDR3 is PC3, DDR4 is PC4.
The number paired after DDR refers to the number of megatransfers per second (MT/s). For example, DDR3-1600 RAM operates at 1,600MT/s. The DDR5-6400 RAM mentioned above will operate at 6,400MT/s—much faster! The number paired after PC refers to the theoretical bandwidth in megabytes per second. For example, PC3-12800 operates at 12,800MB/s.
It is possible to overclock RAM, just like you can overclock a CPU or graphics card. Overclocking increases the RAM’s bandwidth. Manufacturers sometimes sell pre-overclocked RAM, but you can overclock it yourself. Just make sure your motherboard supports the higher RAM clock speed!
You might be wondering if you can mix RAM modules of different clock speeds. The answer is that yes, you can, but they’ll all run at the clock speed of the slowest module. If you want to use faster RAM, don’t mix it with your older, slower modules.
You can, in theory, mix RAM brands, but it isn’t advisable. You run a greater chance of encountering a blue screen of death or other random crashes when you mix RAM brands or different RAM clock speeds.
Timing and Latency
You will sometimes see RAM modules with a series of numbers, like 9-10-9-27. These numbers are referred to as timings. A RAM timing is a measurement of the performance of the RAM module in nanoseconds. The lower the numbers, the quicker the RAM reacts to requests.
The first number (9, in the example) is the CAS latency. The CAS latency refers to the number of clock cycles it takes for data requested by the memory controller to become available to a data pin.
You might notice that DDR3 RAM generally has higher timing numbers than DDR2, and DDR4 generally has higher timing numbers than DDR3. Yet, DDR4 is faster than DDR3, which is faster than DDR2. Weird, right?
We can explain this using DDR3 and DDR4 as examples.
The lowest speed DDR3 RAM runs is 533MHz, which means a clock cycle of 1/533000000, or 1.87 ns. With a CAS latency of 7 cycles, the total latency is 1.87 x 7 = 13.09 ns. (“ns” stands for nanoseconds.)
Whereas the lowest speed DDR4 RAM runs at is 800MHz, which means a clock cycle of 1/800000000, or 1.25 ns. Even if it has a higher CAS of 9 cycles, the total latency is 1.25 x 9 = 11.25 ns. That’s why it’s faster!
For most people, capacity trumps clock speed and latency every time. You will get much more benefit from 16GB of DDR4-1600 RAM than you get from 8GB of DDR4-2400 RAM. In most cases, timing and latency are the last points of consideration.
Error Correcting Code (ECC) RAM is a special kind of memory module that aims to detect and correct data corruption. ECC ram is used in servers where errors in mission-critical data could be disastrous. For example, personal or financial information is stored in RAM while manipulating a linked database.
Consumer motherboards and processors don’t usually support ECC-compatible RAM. Unless you are building a server that specifically requires ECC RAM, you should stay away from it.
What Is PC4 RAM?
As above, PC4 is another way of detailing the data transfer rate of your RAM. But where DDR4-xxxx details the per-bit data rate, PC4-xxxxx details your RAM’s overall data rate in MB/s. You can find out the total data rate of a RAM module by multiplying its frequency by eight.
Thus, DDR4-3000 refers to a RAM module with a 3000MHz frequency. 3000*8 gives us a total data transfer rate of 24000MB/s.
By extension, PC4 deals with DDR RAM. PC3 deals with DDR3 RAM, and so on. So if someone asks if DDR4 RAM is better than PC4 RAM, know they’re talking about the same thing, just using a different measurement method.
How Much RAM Do You Need?
Long past are the days where “640K ought to be enough for anybody.” In a world where smartphones regularly ship with 4GB RAM or more, and browsers like Google Chrome play fast and loose with their memory allocations, RAM frugality is a thing of the past. The average amount of installed RAM is increasing across all hardware types, too.
For most people, 4GB is the bare minimum amount of RAM you need for a general usage computer. Operating systems have different specifications, too. For instance, you can run Windows 10 on just 1GB RAM, but you will find your user experience sluggish. Conversely, numerous Linux distributions work extremely well with smaller amounts of RAM.
If you find yourself with six Word documents open at any one time, can’t bring yourself to close those 60 tabs in Google Chrome, you will probably want at least 8GB RAM. The same goes if you want to use a virtual machine.
16GB RAM should exceed the needs of most. But if you keep utilities running in the background, with a mountain of browser tabs and everything else, you’ll appreciate the extra RAM capacity. Very few people need 32GB RAM, but as they say, more is more.
A RAM upgrade is definitely one of the easiest ways to get an instant performance boost. However, before committing to an upgrade, check out these common myths and misconceptions regarding RAM. They’ll help you make a better-informed decision about how much RAM you need for your system and whether an upgrade is the best option.
Understanding Everything About RAM
You now know the difference between DDR2, DDR3, and DDR4 RAM, and you’re up to speed on RAM specs.
You can tell a DIMM from a SO-DIMM, and you know how to spot RAM with faster transfer rates and higher bandwidth. At this point, you’re essentially a RAM expert, so it shouldn’t feel overwhelming next time you attempt to buy more RAM or an entirely new system.
Really, if you have the correct form factor and the corresponding RAM generation, you cannot go wrong. Timing and latency do play a role, but capacity is king.
You’ve narrowed the source of your PC’s sluggishness to RAM. What do you do? Increase the amount of RAM? Or would you be better off with faster RAM? It isn’t that straightforward.
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