Laptop Memory Upgrades Guide - Part 2

Types of laptop memory

types of laptop computer memory

Laptop memory just as its desktop counterpart makes use of a range of memory technologies but equally characteristics. You'll want to learn these as they'll prove very helpful once you come round to purchasing your new laptop RAM, especially if you decide not to use any memory tools or scanners that automate the process for you - don't worry, we mention these in part 5 of the Laptop Memory Upgrades Guide. It may seem like a lot to take in at once and understand so with this in mind here's our list of tips that should point you in the right direction to becoming a memory guru:


  • Laptop RAM is only ever FPM, EDO, SDRAM, DDR, DDR2 or DDR3 - different types of memory technologies don't mix
  • All modern laptops use a given type of DDR RAM
  • The newer the memory type the higher its timings but also frequency
  • The newer the memory type the lower its operating voltage
  • Only newer types of DDR, DDR2 and DDR3 RAM support dual channel operation
  • The vast majority of laptop RAM is unbuffered and non-ECC


RAM in principle

Before we embark on showcasing the various different memory technologies we want to make sure you understand what RAM really is, technologically speaking. Fortunately, the principle is simple and if you grasp this you'll also be quick to understanding how memory has evolved and become more efficient over the years. RAM is comprised of a series of rows and columns which form cells where data is stored. If you remember from part 1 of the Laptop Memory Upgrades Guide we said that electronic data can at any time find itself within RAM. Simple enough? Let's take this a step further - any data found in RAM will in effect be stored in these cells. The speed in which data can be written, read or copied to and from these cells largely influences the speed of RAM. By following this logic we can see that each and every memory technology discussed below is in effect the efficiency in which instructions involving these cells can be executed.



Memory technologies

FPM (Fast Page Mode)

FPM RAM is the oldest type of memory you will most likely ever come across. While earlier laptops that used older DRAM memory did exist, it was not until the mid 90's when laptops started becoming readily available. Should you be lucky enough to own an older laptop from around this timeframe then there is a very high probability it will either use FPM or EDO memory. If you own one that is DRAM based then it can only mean one thing, you must be an antique collector.


The term FPM is actually misleading by today's standards as there is nothing "fast" about it in comparison to more modern RAM. It was dubbed "Fast Page" over previous DRAM memory because it does not need to re-access the row (specifically its address) for subsequent requests issued by the memory controller if the latter correspond to the same row just serviced for the current request. Because this essentially removes a delay providing the row address stays constant, FPM memory is somewhat faster than DRAM memory.


Should I upgrade a FPM memory based laptop?

FPM memory based laptops are considered vintage computing by today's standards. Memory technology has come a long way since FPM and so any laptops that use it are very old. Nevertherless, if you do own such a laptop and want to relive some nostalgia then why not upgrade, for all other reasons it's probably best you don't. Do keep in mind that if you do decide on upgrading, FPM RAM isn't no longer produced, as a result you'll need to buy it second hand.


EDO (Enhanced Data Output)

EDO RAM is one the older types of memory you are most likely to encounter if you own and wish to upgrade an older laptop. Such laptops were produced around the mid 90's up until around 1997 when SDRAM entered the market. EDO is an evolution to FPM and in a similar way to the benefit of FPM over conventional DRAM memory, it also provides an added boost in performance. This is achieved via enhancing the way in which EDO RAM transfers data back to the processor via a request from the memory controller. In DRAM and FPM there was a bottleneck such that the memory could not transfer a series of data back to the memory controller (enroute to the processor) without first completing a single transfer. This means transfers had to be sequential - each had to be processed one at a time. EDO changed this in that the memory could start processing a request for a subsequent transfer of data (issued by the memory controller) before completing the current transfer. In effect, this enabled EDO memory to fetch the subsequent data ready for transfer at the same time to transfering the current series of data.


Both FPM and EDO RAM is similar and so an interesting aspect to keep in mind is that many laptops from the same production timeframe support both FPM and EDO. This is good news since it means you can in some cases remove all FPM memory from your laptop and upgrade to EDO memory. The only exception is when at least some memory is soldered onto the motherboard in your laptop by its manufacturer and it just happens to be of the FPM variety. The good news is that this was never overly popular and so there is a high probability to successfully upgrade an older laptop currently using FPM memory to EDO memory. While such a move will not turn your older laptop into a speed demon, it is nevertherless a valid means to squeezing some more performance out of it.


Should I upgrade an EDO memory based laptop?

EDO memory is faster than FPM memory but by no means is it a speed demon. Consequently, if you have an older laptop currently using FPM RAM and choose to upgrade then don't expect a miracle. If upgrading from FPM to EDO RAM in your laptop, first of all make sure the memory controller supports the latter - many did at the time but not all. Similarly to upgrading FPM RAM also consider that EDO RAM isn't produced these days so you'll have to go buying it second hand.


SDRAM (Synchronous Dynamic Random Access Memory)

SDRAM laptop memory is a much newer and more efficient type of RAM. One of the two main differences over previous memory technologies is the fact it's synchronous. This means it operates in tune with the processor's data bus, this in turn being the logic linking the processor to the memory controller - the latter in SDRAM based laptops is directly linked to the memory. As SDRAM operates in line with the processor's bus, there is less delay between both clock signals aligning - the latency between one being ready while the other still completing a clock cycle is drastically reduced. This paves way to the other chief advantage of SDRAM over previous memory technologies, namely a higher clock speed. While FPM and EDO memory operate an up to 66MHz due to the fact they run asynchronously (anything over this is overclocked and not guaranteed), SDRAM is certified for speeds of up to 133MHz.


SDRAM was popular in laptops from the very late 1990's to the early 2000's. Unfortunately it's rare for a laptop from that production cycle to support both SDRAM and an older memory technology such as EDO. The underpinning for this is simple, doing so would mean taking up more space within the laptop chassis since SDRAM uses a different type of memory module as explained in part 3 of the Laptop Memory Upgrades Guide. The good news for SDRAM based laptops is that they offer a much higher memory bandwidth over FPM/EDO memory which is why in practise they represent a big jump from older FPM or EDO memory based laptops. Even processors in the mid to late 1990's were heavily bottlenecked by the limitations of FPM and EDO.


Should I upgrade a SDRAM memory based laptop?

SDRAM based laptops are technically considerably more modern than older FPM or EDO RAM based laptops which in turn makes them more usable, even today if you take into account basic tasks. Should you own such a laptop and find use for it then they are still worthy of an upgrade.


DDR (Double Data Rate)

DDR laptop memory represents the oldest type of the newest wave of memory technology used in laptops. While it's referred to as DDR it's in fact DDR SDRAM - an evolution to the older SDRAM. DDR is a solution to a problem that has existed ever since processors have been advancing at a vast pace - limiting the performance bottleneck between memory and processor. DDR enables this by essentially doubling the throughput over SDRAM. In technical terms this is made possible through transferring a series of data on both the rising and falling elements of each memory clock cycle resulting in an effective two concurrent transfers. Clock speed is also evolved over SDRAM up from 133MHz to 200MHz (400MHz effective). The result is a maximum two-fold increase in bandwidth over SDRAM at the same clock speed or up to a three-fold increase if to take into account its technical advantage and maximum certified clock speed of 200MHz. This performance rises further through the use of dual channel mode which we'll discuss in part 3 of the Laptop Memory Upgrades Guide.


Should I upgrade a DDR memory based laptop?

Laptops that make use of DDR RAM were made from the early to mid 2000's. If you own and wish to upgrade a laptop from such production timeframe then there is a very high probability it will rely on DDR memory. These laptops are still very usable, especially for simple tasks or older software and so upgrading is a sensible option. The added bandwidth over SDRAM along with a more modern platform in general is the primary reason behind why DDR laptops became the first of the series to be dubbed as "desktop replacements".


DDR2 (Double Data Rate 2)

DDR2 laptop memory is a fairly modern memory technology and one that's very popular in modern laptops. It also offers a substancial boost over earlier memory technologies including DDR. Similarly to the case with SDRAM and DDR, DDR2 is an evolution to DDR. DDR2 increases the performance threshold by a clever design that seperates the clock speed of the memory chips (found on the memory module) and adds a data bus that connects these together running at twice the speed of the memory chips. Since the memory chips on a given memory module are grouped into two groups which operate at a slightly shifted clock speed, and the data bus on the memory module operates at double their clock speed, this results in up to a two-fold increase in performance over DDR. DDR2 transfers a series of data on both the rising and falling elements of each clock cycle just like DDR but because it also features the above enhancements, this results in an effective four concurrent transfers per memory clock cycle. Clock speed is also evolved in comparison to DDR and is up from 200MHz to 266MHz (533MHz effective). Last but not least, as with DDR, this performance rises further through the use of dual channel mode discussed in part 3 of the Laptop Memory Upgrades Guide.


Should I upgrade a DDR2 memory based laptop?

Laptops that use DDR2 RAM were made from the mid 2000's to about 2009 when DDR3 started taking over. If you own and wish to upgrade such a laptop then there is a very high probability it will use DDR2 memory. These laptops are modern thus very usable, upgrading them is fully warranted. The added bandwidth over DDR along with a further enhanced higher performing platform meant that many DDR2 laptops were marketed as "desktop replacements".


DDR3 (Double Data Rate 3)

DDR3 laptop memory is currently the newest memory technology and is rapidly gaining deployment in new laptops. DDR3 is yet again an evolution to an earlier version of DDR, in this case DDR2 and offers yet another boost in performance, something that the latest processors put to very good use. This is mainly achieved by doubling the data bus speed first introduced in DDR2. If you remember, in DDR2 the data bus operated at twice the speed of the memory chips. DDR3 doubles this yet again and so the data bus of DDR3 memory runs at quadraple the speed of the memory chips. Consequently, DDR3 memory can deliver the same bandwidth as DDR2 memory but at half the memory clock speed of the latter. This performance rises further through the use of dual channel mode discussed in part 3 of the Laptop Memory Upgrades Guide


Due to manufacturing improvements over the years, DDR3 RAM uses less voltage than both DDR and DDR2 (including of course all earlier memory technologies) at 1.5V vs 1.8V for DDR2 and 2.5V for DDR. Using less voltage paves the way for cooler running memory modules that are more energy efficient - something of meaningful relevance in laptops where battery life and cooling is limited. Interestingly, memory voltages would not be able to fall as drastically as they have from DDR to DDR2 to DDR3 if these combined technological efficiencies were not implemented. Improvements in the manufacturing process of memory chips over the years would not singly result in such benefits given the vast increase in effective memory clock speeds ever since the days of FPM and EDO memory. All this makes DDR3 RAM very high performance, able to deliver memory bandwidths far in excess of previous DDR or DDR2.


Should I upgrade a DDR3 memory based laptop?

Laptops which use DDR3 RAM were predominantly introduced in 2009. If you own such a laptop and believe the tasks you use it for could benefit from additional memory, upgrading it is a truly feasible option. The sheer attainable bandwidth over DDR2 means that DDR3 laptops are true "desktop replacements" in every sense of the word.


Memory characteristics

Memory frequency (measured in MHz)

All laptop memory is of a certain specified frequency which is measured in MHz. The latter is the basic measurement used worldwide in various electronic devices. In the case of laptop RAM, it denotes the frequency at which the memory operates. A hertz (Hz) is defined as a complete cycle, consequently a MHz is otherwise one milion complete cycles. The higher the number the faster the RAM and generally speaking, the more modern it is too.


Laptops have commercially been with us ever since the early 1990's. At that time they used FPM RAM which usually operates at a speed of 50 or 60MHz. A few years later EDO RAM became the norm but while superior in performance it also only operated at 66MHz. It was not until the late 1990's when SDRAM became available did RAM speeds considerably increase. A typical frequency for SDRAM laptop memory is 66-133MHz. Through the years when DDR came to surface RAM frequencies extended up to 200MHz. Frequencies progressed from there and modern RAM such as DDR2 operates at up to 533MHz. The currently latest type of RAM known as DDR3 operates at frequencies of up to 666MHz, otherwise denoted as an effective speed of 1.33GHz.


For the trained eye it's usually possible to determine the speed of RAM by looking at the memory chips soldered onto a memory module, We'll discuss these in part 3 of the Laptop Memory Upgrades Guide. This is achieved by looking at the last digit or two digits laser inscribed onto the memory chips. For example, the markings "-10" suggest an access time of 10ns. If we devide 1000ns (1 second) by this number then we'll discover the frequency of this RAM, namely 100MHz. Likewise, a marking of "6" yields a frequency of 133MHz. In both these examples one would normally expect these two to be SDRAM. In reality however, you would look at different aspects before making a qualified guess.


When preparing to order and thus install a laptop memory upgrade keep in mind the following: will you be removing all the current RAM and just installing brand new laptop memory modules? Alternatively, will you be keeping the existing RAM and adding the newly purchased laptop memory?


If you answered the former, that is you intend to remove all the current RAM and install new RAM modules in their place then there is nothing to be concerned with - simply order and install the highest type and frequency of RAM your laptop supports. If however you answered the latter, that is you will keep the current memory and merely add new RAM modules, you need to remember to purchase a laptop memory upgrade that is of the same type but equally same or higher RAM frequency to that already installed. Failing to do this will mean your laptop either operating at a slower memory speed, or in the worst case not operating at all. Sometimes laptop manufacturers install faster memory than what is necessary, in other words memory that can run at higher frequencies to what the memory bus operates (or can operate) at in the given model of laptop. In such cases the latter advice would not apply but it's best to always check. As for why laptop manufacturers occasionally install faster RAM, it's quite simply a case of economics. As they buy in bulk, they sometimes encounter the possibility to buy faster speed grade memory cheaper at the price of a lower speed grade. Various aspects can influence the "how" and "why" with a classic supply and demand relation being the dominant force.


Memory timings (CL or CAS, tRCD, tRP, and tRAS)

Laptop RAM is comprised of a series of rows and columns which in turn make up cells inside the memory chips themselves where data is stored once the laptop is turned on. If you remember, we touched on this in part 1 of the Laptop Memory Upgrades Guide. This is essentially a vast grid, the more RAM installed within your laptop, the larger the grid becomes. As with all electronic devices, they can only reliably operate within a given realm which in the case of RAM is determined by the deployed memory technology. RAM participates in various operations each time the memory controller reads or writes to any of its cells in the grid. In basic terms we can define this as three seperate stages:


  • A) Setup
  • B) Read or write
  • C) Closure/refresh

Each stage must take a finite amount of time for the RAM to operate reliably thus maintain stability and avoid memory errors. Memory timings specify the rate at which these occur. A laptop just as any computer configures these parameters when first turned on through what is know as the BIOS (Basic Input Out System) - a piece of software that is run when the on/off button is pressed. There are various timings used to configure its mode of operation, most of which are hidden from the user and cannot be changed from within the BIOS. There is in fact a very good reason why, these hidden timings seldom boost performance but often affect memory stability.


RAM is sold on the condition that it can reliably operate at a given set of timings, at a given memory frequency and at a given voltage. The four main memory timings are:


  • CL/CAS - CAS Latency or Column Address Strobe - This is the delay between the time when the memory controller present within the laptop informs the memory to access a given column and the time whenthe location within the memory is ready to be accessed
  • tRCD - Row Address to Column Address Delay - This is the number of clock cycles necessary between opening a row of memory and accessing columns within that row
  • tRP - Row Precharge Time - This is the number of clock cycles necessary between the issuing of the precharge command and opening the next row
  • tRAS - Row Active Time - This is the number of clock cycles necessary between a bank active command and issuing the precharge command

The memory timings supported by the memory module heavily depend on the memory technology it uses. For example, older RAM featured slower speeds hence could support lower timings such as 3-3-3-5. Modern RAM ventures in the opposite direction, that is it operates at faster frequencies but does so at the expense of slower memory timings. The underpinning for this is that when increasing memory clock speed (in general terms the effective memory speed) durations of memory operations do not progress in a linear fashion. Select additional delays (latencies) must be introduced to ensure stability. In general terms, the lower these numbers the better (faster) the given RAM module - though clock speed will always be a larger contributor to overall memory performance. For example, the gains in memory performance between memory timings of 4-4-4-12 and 3-4-4-8 are neglible and you would normally not feel the difference in general use. This difference, though still minor, would only be represented in benchmarks. Consequently, if you do wish to opt for the best performance from the laptop RAM you buy, keep in mind that CL/CAS has the biggest performance impact from all the above memory timings. Typical memory timings (CL or CAS, tRCD, tRP, and tRAS) depending on the memory technology are as follows:


  • FPM & EDO - 3-2-2-2 & 3-3-3-3
  • SDRAM - 3-3-3-8
  • DDR - 3-3-3-8
  • DDR2 - 4-4-4-12
  • DDR3 - 7-7-7-20

Modern RAM features a SPD (Serial Presense Detect) chip located (soldered) on the memory module that has been programmed to allow the BIOS to automatically setup appropriate memory timings (and other aspects such as voltage) when the laptop is turned on. Older FPM and EDO memory features what's knwon as a PPD (Parallel Presence Detect) - this is similar except stores fewer configuration data.


When preparing to order and thus install a laptop memory upgrade keep in mind the following: will you be removing all the current RAM and just installing brand new laptop memory modules? Alternatively, will you be keeping the existing RAM and adding the newly purchased laptop memory? You may get a feeling of deja vu as we've asked you to think about these questions before haven't we? In fact, we introduced them above when discussing memory frequency. Fortunately, we've not tired in writing this guide, these questions are still relavant when it comes to memory timings. Let's take a look why.


If you answered the former, that is you intend to remove all the current RAM and install new RAM modules in their place then there is nothing to be concerned with - simply order and install the highest type and frequency of RAM your laptop supports. If you admire every ounce of performance, order memory modules with the best memory timings you can afford. If however you answered the latter, that is you will keep the current memory and merely add new RAM modules, you need to remember to purchase a laptop memory upgrade that is of the same type, same or higher RAM frequency to that already installed and same memory timings. If you don't and end up mixing memory modules supporting different memory timings at the same frequency then your laptop will likely still run just fine albeit at the level of the slower memory timings. The BIOS examines the supported memory timings by all memory modules and ultimately sets the lesser to ensure system stability.


Memory voltage (measured in volts)

All laptop RAM regardless whether it incorporates old or modern memory technology operates at a given voltage. This is the electrical current that enables it to operate within its specification while mantaining stability. Older RAM in the form of FPM and EDO memory runs at 5 or 3.3V. SDRAM runs at either 5 or 3.3V. DDR as a newer type of memory only needs 2.5 or 2.6V, DDR2 1.8V and DDR3 1.5V.


Sometimes you'll find RAM being offered which runs at voltages slightly exceeding these values. This is usually because the RAM on offer is certified to run at faster memory timings, or possibly a higher memory speed (normally known as overclocked). This form of laptop RAM is only worth purchasing for modern select laptops due to the fact that the latter have advanced BIOS's which allow overclocking options, including increasing memory voltage. Notice that we threw the word "select" in that last sentence, keep in mind that only high-end laptop models feature such advanced BIOS's - gaming laptops are the top of this list. Older laptops will in the vast majority of cases not benefit from such performance laptop RAM and it may even pose a problem if the onboard VRM (Voltage Regulator Module) cannot supply the higher voltage. Should this be the case, you will either have to lower the memory timings manually in the BIOS (thus eradicate any performance boost from the increased memory timings, or headroom for a higher memory speed) or potentially suffer from stability issues during normal use of your laptop.


Modern laptop RAM features a SPD (Serial Presense Detect) chip on the memory module that has been programmed to allow the BIOS to automatically set appropriate voltage. Some memory modules take this a step further and include a 3rd party version of SPD somewhat extending the capabilities of a standard SPD, one such example is Intel's X.M.P. (Xtreme Memory Profiles). Older laptop RAM such as DDR relies on the BIOS to setup the standard operating voltage despite also featuring a SPD chip - voltage information stored in the SPD was only introduced along with DDR2. Old laptop RAM such as FPM and EDO stores no voltage information and in a similar way to DDR relies on the BIOS to setup the memory voltage. In very old laptops the memory voltage is sometimes set manually by jumpers on the laptop's motherboard and once set (usually to one of only two settings) does not need to be set again for the lifetime of the laptop. The only exception to this rule would be if you were upgrading an old laptop that currently has FPM memory operating at 5V, and you wish to install EDO memory (providing it's compatible with your laptop) which operates at 3.3V. In most cases you should not be concerned about the memory voltage when purchasing your modern laptop memory upgrade.


Unbuffered (unregistered) & buffered (registered)

When looking to buy a laptop memory upgrade it's useful to know the difference between unbuffered and buffered memory, sometimes also referred to as unregistered and registered memory. You'll find that very seldom does a laptop require buffered RAM and the vast majority of laptop RAM is indeed of the unbuffered variety. What's the difference between the two?


Unbuffered laptop RAM is a type of memory that supports direct access to it by the memory controller in your laptop, in other words when there is a read or write request issued by the memory controller, it accesses the RAM modules directly. Buffered memory is the opposite in that when a read or write request is issued by the memory controller, the memory controller accesses the buffered area of the memory modules rather than the RAM modules directly. The buffered area is an additional chip on each RAM module that stores data to and from the given RAM module. If the memory controller issues a read request, the corresponding RAM module will first cache (buffer) the concerning data into its buffer before transmitting it further to the memory controller. Likewise, if the memory controller issues a write request, it will transmit the data to the corresponding RAM modules buffer before this data is once again transmitted further and stored in a given cell within that memory module. The reasoning for buffered memory is to ensure stability in systems that contain many populated memory slots as the electrical current deteriorates over a certain number, this in turn due to the simple fact that the current must pass through each installed module and yet be robust enough to not cause stability issues.


Parity

Parity is a form of error detection mechanism built into some computer RAM. It' usually very rare to be found in laptops due to the simple fact that data integrity is not classified as important in laptops, that is they're not used for mission critical tasks that heavily rely on software (memory) errors being detected before potentially leading to system instability. Parity works by storing an extra bit (the smallest unit of measurement used in computers) for each 8 bits (equal to 1 byte) of stored data - this single bit is used to later validate if the data formed within the preceding 8 bits is error free. Unfortunately storing 9 bits for each 8 bits isn't without faults, namely parity RAM can only detect smaller errors.


There's a very high probability that your laptop doesn't support parity memory and thus it's not possible to use such RAM even if you manage to buy some. Do however remember that should the case be the opposite, that is your laptop does support parity, you cannot mix and match parity and non-parity (standard) RAM modules at the same time. It's more likely you laptop supports ECC RAM so let's take a look at it next.


ECC (Error Correction Code)

ECC is a more advanced form of error detection mechanism to parity. It's usually rare to be found in laptops due to the simple fact that data integrity is not classified as important in laptops, that is they are not used for mission critical tasks that heavily rely on software (memory) errors being detected before potentially leading to system instability. You've heard us say the same about parity RAM above haven't you? You'll be glad to discover that while both parity RAM and ECC RAM concern system stability, they actually work differently.


The difference between parity RAM and ECC RAM is that the latter not only detects memory errors but also corrects them in real-time. ECC RAM uses extra bits of data instead of just a single bit to validate stored user data, in other words data somehow related to the software run on the system. ECC RAM scans this data on a continuous basis and if an error is found, it seeks to correct it. Because multiple additional bits of validation data are stored ECC RAM is actually very efficient at correcting these errors. This process is performed transparently to the system thus user, the only time when the latter come to realise something adverse has happened is when a severe memory error has occured and cannot be corrected. ECC RAM is slower than conventional RAM because of both the additional processing times necessary for error correction but also the somewhat more laxed memory timings this action imposes.


There is a high probability that your laptop does not support ECC RAM and thus it's not possible to use such laptop memory. If however you own a high-end workstation class laptop then it may support ECC RAM. These are sometimes known as mobile workstations and chiefly targetted for professional CAD or CAM work.


Memory standards

JEDEC (Joint Electronic Device Engineering Council(s))

JEDEC is the institution that develops memory standards used in computers, be this laptops, netbooks, desktops or servers - it's all one family. While it's not vital you learn and appreciate the technicalities behind the memory standards themselves, it's helpful to get a glimpse of their names as you'll come across these when buying your next laptop memory upgrade.


In most cases laptop memory strictly follows JEDEC specifications, however on occasions you may encounter memory that:


  • A) Features a higher number in its name (i.e. PC2-7100 Vs PC2-6400)
  • B) Runs at a different voltage despite being the same type (i.e. DDR2)
  • C) Has tighter memory timings (i.e. 5-5-5-15 Vs 7-7-7-20)

It's far less likely you'll encounter any of the above when searching through which laptop memory upgrade to buy as this is something much more the domain of desktop memory upgrades. If you do come across any of the above though then it helps to understand what this really means. JEDEC is the governing body that releases memory standards into the market. All memory that corresponds to such standard must at least operate within the realms it sets out. Consequently, all memory manufacturers within the market need to ensure that their RAM 100% complies with these specificatons. Notice that this means all manufactured memory must meet these specifications - whether they exceed them is entirely up to the given manufacturer.


Some laptop manufactures including memory brands choose to exceed JEDEC specifications as a way to differentiate their produts from the competition. This approach equally allows them to market their products to the enthusiast niche, and as is convenient to do so, charge extra for the privalge. Because few laptops allow overclocking it's very rare to find laptop RAM that is certified to run at a higher frequency to that stated by the corresponding JEDEC standard. The same applies to memory voltage. The most likely variant you'll encounter is (C) as denoted above - RAM modules have been certified to run at the corresponding JEDEC standard albeit at tighter (thus faster) memory timings. The latter will have been programmed in to their SPD so your laptop's BIOS sets them up upon turning on your laptop.


Of course, in order to tell apart what is a JEDEC standard name from that which isn't, you need to know what the official JEDEC standard names are. With this in mind below are some useful JEDEC standards to help you easily differentiate laptop RAM:


  • FPM/EDO - 70ns or 60ns respectively, 60-66MHz at 5V or 3.3V at 3-3-3-6/2-2-2-6**
  • SDRAM - PC66 (66MHz), PC100(100MHz), PC133(133MHz) at 5V or 3.3V at 3-3-3-6**
  • DDR - PC1600 (200MHz*), PC2100(266MHz*), PC2700(333MHz*) and PC3200(400MHz*) at 2.5-2.6V at 3-4-4-8**
  • DDR2 - PC2-3200(400MHz*), PC2-4200(533MHz*), PC2-5300(667MHz*), PC2-6400(800MHz*), PC2-8500(1066MHz*) at 1.8-2.2V at 5-5-5-15**
  • DDR3 - PC3-8500(533MHz*), PC3-1333(667MHz*), PC3-1600(800MHz*) at 1.5V at 7-7-7-20 or 9-9-9-24**

* - effective memory frequency

** - typical memory timings


Go back and read about Laptop memory and how it affects the performance of your laptop...

...or continue reading to learn about the Types of laptop memory modules.

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