Meet Your Mobile Memory
Memory is every bit as important on a laptop as it is on a desktop PC. Arguably, it may be even more important on a notebook since, in general, portable systems are likely to have slower processors and smaller storage drives than their desktop counterparts. This places even more stress on the memory. If it’s too slow or too small, the entire system will suffer. Let’s take a close look at laptop memory and how it can be upgraded.
Small outline dual in-line memory modules (SODIMMs) are much like the regular DIMM memory used in desktop PCs, but SODIMMS generally place chips in two rows so as to be narrower and more compact (6.76 x 3.175 cm). Over time, SODIMMs have been made in 72-, 100-, 144-, 200-, and 204-pin designs. DDR/DDR2 modules use the 200-pin format, and DDR3 is 204-pin. The edge connector notch (“key”) position varies across SODIMM types.
In the days before DDR, notebooks typically used 144-pin SDRAM. Sporting modules by PQI, this 512 MB module operated at 3.3V and used a clock frequency of 133 MHz (PC133). PC133 was the last SDRAM standard ever approved by JEDEC. Computers that could run PC133 were also backward compatible with PC66 and PC100 modules. The maximum bandwidth for PC133 was 1066 MB/s.
The first step into DDR (double data rate) SODIMMs came with PC1600, also known as DDR-200. The internal clock rate of 100 MHz yielded an actual data rate of 200 MT/s (200 million transfers per second). DDR SODIMMs scaled up to include DDR-266, -333, and -400 specifications, with DDR-400 (PC3200) sporting a peak transfer rate of 3200 MB/s. The module shown here is a 64 MB PC2100 unit. Note the two edge connector keys.
By the time DDR SODIMMS arrived, some buyers recognized that notebooks could also be high-performance PCs. One ingredient of high performance is optimized memory. There are a number of memory timings that convey the time delays involved in various functions within the module. First and most important among this is CAS latency (CL). This image shows the CL2.5 timing on a Samsung DDR-266 SODIMM. In general, lower timings yield faster performance.
The “double” in double data rate (DDR) comes from the manner in which data transfers on both the rising and falling edges of a memory module’s clock signal. However, whereas DDR memory is clocked at one-half the rate of the bus, DDR2 is clocked at one-quarter of that rate, effectively doubling the data transmission speed. Additionally, DDR2’s typical voltage dropped to 1.8V from original DDR’s 2.5V. Shown here is a DDR2-800 (PC2-6400) module.
Official DDR2 specs topped out at DDR2-1066 (PC2-8500). It’s interesting to note the inverse relationship between clock rates and timings. DDR2-400 offered official timings as low as 3-3-3, but DDR2-1066 only went down to 6-6-6—a sort of two steps forward and one back affair. Many vendors marketed modules with more aggressive specs than those sanctioned by JEDEC. Vendors also started selling modules in pairs as dual-channel system architectures prevailed.
DDR3 transfers data at eight times the internal clock rate. JEDEC specs lowered DDR3 voltages down to a typical 1.5V and provided for chips of up to 8 GB. Official DDR3 standards run from DDR3-800 (PC3-6400, CL5 or CL6) up to DDR3-2133 (PC3-17000, CL11 to CL14). As with prior DDR formats, DDR3 SODIMMs can optionally include error correcting code (ECC) or be “registered” for improved signaling, both features common in business systems.
Image via http://bit.ly/Lab1og. Attribution: Tobias b köhler, under Creative Commons Share Alike 3.0 license.
Desktop memory manufacturers are fond of applying heatsinks to their higher-end modules. The premise is that accelerated or overclocked modules generated excess heat that needed to be radiated into the PC more efficiently in order to let them operate at higher levels. Some critics suspect there’s more bling than benefit to these products. Despite there being almost no airflow inside of notebooks, a few SODIMM vendors are starting to follow suit.
The XMP Jump
The Kingston HyperX module on the preceding page, as well as these Corsair Vengeance SODIMMs, represent the apex in today’s enthusiast notebook memory space. Both have models topping out at PC3-15000 (1866 MHz), and both support XMP. Extreme Memory Profile is a JEDEC-approved DDR3 extension, devised by Intel, that will automatically overclock system memory according to given profiles when used in conjunction with certain CPU platforms.
Begin the Upgrade
Many people (not Tom’s readers...just other people) still view notebooks as inscrutable black boxes that only a manufacturer can touch with a screwdriver. Much as manufacturers love this service revenue, the reality is that most notebook owners can upgrade their SODIMM memory in only a couple of minutes and with no tool more specialized than a $2 set of jeweler’s screwdrivers. Let’s see how it’s done.
Remove the Cover
Most PC notebooks have a few panels on their bottoms, one of which will reveal the memory slots. (Some models only make one slot available and hide the other under the keyboard, which is a pain but entirely manageable if you’re careful.) This service diagram for Apple’s MacBook Pro shows how the entire bottom of the notebook comes off in order to give access to the internal components.
Insert the Module
SODIMMs sockets normally mount modules so that, when inserted properly, the module lays parallel to the motherboard. Two clips on each side of the socket hold the module in place. All you do is alight the edge connector key on the SODIMM with the corresponding bump in the socket, slip the SODIMM into the socket at an angle, and then press down. Put the cover back on and reboot the system.
DIY and ESD
There is one very real danger when doing your own memory upgrades: electrostatic discharge (ESD). All of us have “zapped” ourselves when the weather gets dry, especially after petting animals or walking in socks across a carpet. This photo shows what static discharges can do at the microscopic level to circuits. It’s like a bomb going off. So always ground yourself on a large metal object to discharge any static buildup before touching PC components.
Despite the process’s simplicity, it’s still possible to botch a SODIMM upgrade. One of the most common missteps is to not seat the module completely into the socket. Even if you get the notch aligned properly, check to make sure that the edge connector looks inserted equally all the way across. If there’s a tilt to the module’s insertion, one side may not be making proper contact.
When you press down on the SODIMM module after inserting it into the memory slot, note the retention clips on each side of the slot. It’s very important that both of these fall solidly into place. Usually, you will hear a click when the clip snaps into place. If you don’t, the module may not be seated deep enough in the slot. If both clips aren’t properly holding the module, it may jiggle loose and unseat as the notebook gets jostled about.
The main reason why we have JEDEC and DRAM standards is to ensure that most any compliant part will work in any compatible system. Any DDR3 SODIMM should work in any system with DDR3 slots. However, historically, there were problems that could arise from mismatching modules, and some people continue to worry over this. If nothing else, the faster chip will be forced to perform at the rate of the slower one.
SO-DIMM’s modularity requires more physical space for the memory sockets and for modules to stand up from the motherboard. An increasing number of vendors are dispensing with SO-DIMMs on ultralight designs, such as the MacBook Air. Here, from iFixit’s mid-2011 teardown of the 13” Air, you can see 4 GB of Hynix memory (outlined in red) soldered directly onto the mainboard. This is great for space savings, but upgrading becomes impossible.
The Little Card That Couldn’t
SODIMMs aren’t the only form of notebook memory. In 2007, Intel Turbo Memory (ITM) debuted, featuring 1, 2, or 4GB of NAND memory mounted on a mini-PCIe card that installed in notebooks much like a SO-DIMM. The PC used this solid state cache to help load files faster. Sadly, ITM was plagued by driver problems and soon died. Today, some of ITM’s concepts live on in “hybrid” hard drives, which incorporate NAND memory.
DDR3 is far from the last word in notebook memory. DDR4 has been under construction at JEDEC since 2005, and the first samples, such as the Hynix modules shown here, started to appear in 2011. The format drops typical input voltage down to 1.2V from DDR3’s 1.5V, and speeds from 2133 to 4266 MT/s are expected. So if you thought your current notebook memory was fast...you haven’t seen anything yet.