RAM is the short-term memory of the computer. It's where your computer keeps track of the programs and data you're using right now. You probably already know that having more RAM installed is generally better for your PC.

Choosing RAM can be confusing. What is 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?
We'll better explain the different types of RAM, how to read the specifications and how exactly they work.

What is RAM?

RAM stands for Random Access Memory. It acts as a middle ground between the small superfast cache in the CPU and the large super-slow memory of the hard drive or solid state drive (SSD). The system uses RAM to temporarily store the working parts of the operating system and the data actively used by applications. RAM is not a form of permanent storage.

Think of your computer as an office. The hard drive is the archive in the corner. RAM is like an entire office workbook, while the CPU cache is similar to the actual workspace where you actively work on a document.
The more RAM you have, the more things you can have quick access at any time. Just as having a larger desk can hold multiple pieces of paper on it without becoming messy and bulky (as well as requiring multiple trips back to the archive to rearrange).

Unlike an office, however, RAM cannot serve as a permanent storage space. The contents of the system RAM are lost as soon as the power is turned off. Losing energy is like cleaning your desk from every document.



Meaning of RAM

When it comes to RAM, we usually talk about synchronous dynamic RAM (SDRAM). SDRAM is what this article also discusses. For most desktops and laptops, RAM is a small rectangular board that you can insert into the motherboard.
Unfortunately, there is a growing trend for super thin and lightweight laptops to have the RAM welded to the motherboard directly in the interest of saving space. However, this sacrifices upgradeability and repairability.
Don't 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 to replace SDRAM. It's highly unlikely that you'll encounter SRAM in general use, so it's not something you should worry about.

RAM form factors

For the most part, RAM comes in two dimensions: DIMM (Dual In-Line Memory Module), which is located on desktops and servers, and SO-DIMM (Small Outline DIMM), which is found on laptops and other small computers.
Although the two RAM form factors use the same technology and functionally work exactly the same way, you can't mix them. You can't put a DIMM stick in a SO-DIMM slot and vice versa (pins and slots don't line up!)

When buying RAM, the first thing to understand is its form factor.


What does DDR mean?

The RAM used on your computer works by using Double Data Rate (DDR). DDR RAM means that there are two transfers per clock cycle. The latest 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 generations of RAM are exactly the same physical size and shape, they are not yet compatible. DDR3 RAM cannot be used on a motherboard that supports DDR2 only. Similarly, DDR3 does not fit into a DDR4 slot. To avoid any confusion, each generation of RAM has a notch cut in the pins in different positions. This means that you can't accidentally mix RAM modules or damage the motherboard, even if you buy the wrong type.


DDR2 is the oldest type of RAM you are likely to encounter today. It has 240 pins (200 for SO-DIMM). DDR2 is obsolete, but you can still buy in limited quantities to upgrade older machines.


DDR3 was released as far back as 2007. It has now been officially replaced by DDR4 in 2014.
DDR3 RAM has the same number of pins as DDR2. However, it works in a lower voltage and has higher timings, so they are not compatible. In addition, DDR3 SO-DIMM have 204 pins compared to 200 Pins of DDR2.


DDR4 has been in the market since 2014. The latest generation of AMD and Intel CPUs only use DDR4 RAM. This means that if you want to upgrade to a more powerful CPU, you need a new motherboard and new RAM.
With DDR4, RAM voltage drops further, from 1.5 V to 1.2 V, increasing the number of pins to 288.


DDR5 has entered the consumer market during November 2021.
DDR5 will continue with a 288-pin design, although the RAM voltage will drop to 1.1 V. DDR5's operating frequencies are higher compared to the previous DDR4 generation. For example, SK Hynix revealed the technical details of a DDR5-6400 RAM module, as fast as the DDR5 standard allows.
But, as with any new computer hardware, it is not recommended to buy it at launch due to extremely high prices for these models. Also, if you're thinking of buying a new motherboard, don't focus on DDR5: it doesn't bring any significant performance improvement over DDR4 yet.

Clock speed, transfer, and bandwidth

You may have seen the RAM referenced by two sets of numbers, such as DDR3-1600 and PC3-12800. These references indicate the generation of 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 and DDR5 is PC5.

The associated number after DDR refers to the number of megatransfers per second (MT/s). For example, DDR3-1600 RAM works at 1,600MT/s. The RAM DDR5-6400 will operate at 6,400MT/s, much faster! The associated number after PC refers to the theoretical bandwidth in megabytes per second. For example, PC3-12800 operates at 12,800 MB/s.
You can overclock RAM, just like you can overclock a CPU or graphics card. Overclocking increases RAM bandwidth. Manufacturers sometimes sell pre-over-clocked RAM, but you can overclock it on their own. Just make sure your motherboard supports the fastest clock of your RAM.
You might wonder if you can mix RAM modules by different clock speeds. The answer is that yes, it's possible, but they'll all go to the slower module clock speed. If you want to use RAM faster, do not mix with older and slower modules. It is possible, in theory, to mix RAM brands, but it is not recommended. You risk random crashes when mixing RAM brands or different RAM clock speeds.

Timings and latency

Sometimes you will see RAM modules with a series of numbers, such as 10-10-10-27. These numbers are referred to as timings. A timing is a measurement of the performance of the RAM module in nanoseconds. The lower the numbers, the faster the RAM reacts to requests.
The first number is CAS latency. CAS latency refers to the number of clock cycles required for the data required by the memory controller to become available for a pin.
You may notice that DDR3 RAM typically has higher timings than DDR2 and DDR4 has higher timings than DDR3. However, DDR4 is faster than DDR3, which is faster than DDR2.

We can explain this by using DDR3 and DDR4 as examples.
The lowest speed for DDR3 RAM is 533MHz, which is 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 plus 13.09 ns. ("ns" stands for nanoseconds)
While the lowest speed DDR4 RAM is 800MHz, that means a clock cycle of 1/8000000000, or 1.25 ns. Although it has a CAS higher than 9 cycles, the total latency is 1.25 x 9 plus 11.25 ns. That's why it's faster!
For most people, capacity is more important than speed and latency. You'll get much more benefit from 16 GB of DDR4-2400 RAM than you get from 8 GB of DDR4-3200 RAM. In most cases, CAS timings and latency are the last points of consideration.

With the same latency, it is always better to choose the kit with the highest frequency.

How much RAM do you need?

For most people, 8 GB is the minimum amount of RAM required for a general-purpose computer. Operating systems also have different specifications. For example, you can run Windows 10 on just 1 GB of RAM, but you'll find your user experience slow. In contrast, many Linux distributions work very well with small amounts of RAM.

If you find yourself using games or graphics applications, you'll probably want at least 16 GB of RAM. The same applies if you want to use a virtual machine. Professional applications may need 32 GB of RAM.

A RAM update is definitely one of the easiest ways to get an immediate increase in overall PC performance.