TYPES OF RAM CHIPS
FOR the most part, the motherboard of the particular computer will determine the type(s) of RAM that can actually be installed on the particular machine. Further, 32 bit Windows can make use of, at most, 4GB of RAM - anything else will be overkill and unusable (see discussion below at Item III). Depending on the age and configuration of the computer, several types of RAM have been and are available:
TIP: Remember: RAM chips are generally incompatible with each other electrically, as well as the number of pins on the chip and also the keys (notches) required to fit into the appropriate motherboard socket. If in doubt, test several chips on the board to see which one(s) fit properly.
[See photos below for representative examples of each type of chip.]
SIMM (Single In-Line Memory Module), older 32 bit bus;
DIMM (Dual In-Line Memory Module), newer 64 bit bus, still old technology; used to be soldered onto motherboard or socket inserted.
RIM (Rambus In-Line Memory Module) Most recent chips, very often with heat sinks to dissipate the elevated operating temperatures.
SO-DIMM (Small Outline Dual In-Line Memory Module), a smaller profile (about half-length) memory module for use primarily in laptops; earlier SO-DIMMS used 72 pins (connectors) and supported 32 bit transfer, but now they typically use 144 pins and allow for 64 bit transfer;
SRAM (Static RAM), stores data using a static method in which the data remains constant so long as power is applied to the chip. Used primarily for cache. Typically uses 4 to 6 transistors for each memory cell, but with no capacitors;
DRAM (Dynamic Random Access Memory), stores each bit of data on a separate capacitor, requiring less space, holding more data, but requires more power because the capacitors must constantly be refreshed, as it uses memory cells with a paired transistor and capacitor. The original DRAM was FPM (“Fast Page Mode”) DRAM, which was slow because it waits through the entire search process of locating a data bit before starting locating the next bit. Maximum transfer rate to L2 cache is about 176 MBps;
EDO DRAM: (Extended Data-Out Dynamic RAM). Slightly faster than FPM DRAM because it does not wait for all processing of the first bid to be complete before continuing to the next bit. Maximum transfer rate to L2 cache is about 264 MBps.
SDRAM (Synchronous Dynamic Random Access Memory), is an improvement to DRAM which was developed in the early 1990s to solve the problem of increasingly powerful computers. While DRAM uses an “asynchronous” interface (meaning it operates independently of the processor itself, not useful if the processor couldn’t keep pace with all of the requests from the processor) SDRAM speeds up the process by “synshconizing” the memory’s responses to control inputs with the system bus, allowing it to queue up one process while waiting for another. because it retrieves data alternatively between two sets of memory. Maximum transfer rate to L2 cache is about 528 MBps. MOST COMMONLY USED TODAY; DDR RAM is a type of SDRAM (see below)
TIP: Remember: RAM chip efficiency is measured by faster transfer rates, at a lower voltage at a lower clock speed.
DDR (Double Data Rate) – As used in DDR-SDRAM, sometimes called SDRAM II – DDR (developed around 2000) transfers data twice as fast as regular SDRAM chips , allowing sending and receiving signals twice per cycle, while the original SDRAM could only accept one command per clock cycle (hence “SDR” or Single Data Rate interface). In addition, the chip became far more efficient, because the memory could run at a lower clock rate (100 - 200Mhz) and, by using less energy (2.5 Volts), achieve faster speeds (e.g. transfer rates up to 400MTps). This efficiency makes this type of memory more suitable for laptop computers since it uses less power than SDRAM. Maximum transfer rate to L2 cache is about 1,064 MBps; Generally, they have TSOP (“Thin Small-Outline Package”) chips in a 184 pin module working at 2.5/2.6 volts up to 3.6 Vdimm.
DDR2 (Double Data Rate 2), which came out in 2003, is just as it sounds, double the rate of DDR memory, an improved version of DDR that was both faster and more efficient, sending data on both the rising and falling edges of the processor’s clock cycles. This refinement utilized an internal clock running at half the speed of the data bus, making it twice as fast as the original DDR, but using even less power (now 1.8 Volts) for a maximum transfer rate of 2,133MTps. But these chips require special slots on your computer, so always check for compatibility; Generally, they have BGA (“Ball Grid Array”) chips, 240 pins and work at 1.8 volts and above (therefore the power requirement of DDR2 is less than DDR, which can work at higher frequencies).
DDR3 (Double Data Rate 3 Synchronus Dynamic RAM): The most common and fastest RAM in use in most current computers today.
DDR4 - The next stage in RAM evolution. Coming soon (2014?) to a computer near you. It is expected to offer transfer rates of up to 4,266MTps, with voltage ranging from 1.05 to 1.2 Volts.
RDRAM (Rambus Dynamic RAM), so named because it is manufactured by Rambus Corp., and it is the fastest type of computer RAM currently available. While SDRAM can transfer data at speeds up to 133 Mhz, RDRAM can transfer at speeds up to 1 Ghz, the chips working in parallel to achieve rates at up to 1,600 MBps. Due to the fast speed of the chip, they often require heat spreaders to dissipate the heat. For laptops, Rambus manufactures SO-RIMMs for laptop computers. Problem is, they’re expensive and, moreover, many boards can’t make use of such high speeds (although many graphics accelerator cards can use them).
Believe it or not, but there are even more types of RAM: (FPRAM, EDRAM, VRAM (for video adapters and 3D accelerators), CDRAM, EDO RAM, BEDO, WRAM, SGRAM (less expensive video RAM than VRAM), SLDRAM and more), but you probably won’t run into these types, so we won’t confuse the issue further. See also, SD CARDS.
Identifying the chip: It’s not always easy to identify RAM just by looking at the chip (unless it’s labeled, of course), and some examples are shown in the photos below, but here are a few guidelines:
- If there are two slots on the pin side of the RAM, it is SD RAM. All DDR chips have only one slot. If you’ve got SD RAM, it’s probably time to upgrade your computer.
- Separating DDR from DDR2 is more difficult. Both have only one slot. But that slot is about 1/16 further up the chip on a DDR2 chip than on a DDR chip - don’t try to force them, you’ll probably crack the chip and the main board! And usually DDR chips have memory modules (the black chips) across the entire face of the chip or the front and back of the chip. The operational speed for DDR (if printed) will usually be 333Mhz or 400Mhz. DDR2 chips, however, will run at speeds from 400Mhz to 1066Mhz; and the memory modules on the face don’t span quite as much real estate as the DDR chips.
- The most common RAM in use on new computers today, DDR3 RAM also ranges in speed between 800Mhz and 1600Mhz. It looks pretty much the same as DDR2 and is hard to distinguish from DDR2. At the moment, this is the predominant chip being used on newer computers.
- DDR4 is on the way, but will take a few years to catch on, so don’t worry about it quite yet..
So how do you know exactly what type and size of RAM suits your computer? Most devices only use one specific type of RAM, some require duplicate chips (e.g. (2) 256Mb chips), and there is an overall limit to the amount of RAM that your device will handle. The only sure way is to look at the existing chip(s) and duplicate them. However, most of the RAM suppliers’ sites have a handy search tool that searches by computer, motherboard and other digital devices and provides you with reasonably accurate information. See, for example, Kingston.com. Another site which can scan your computer, make a recommendation about whether you need to increase the RAM and claims to guarantee compatibility of the RAM they sell is Crucial. Installing RAM isn’t particularly difficult: You just get under the hood and insert the chip into the slot. Usually it will work. If not, keep experimenting with chips until you find one that is accepted by the system BIOS. For this reason, it’s sometimes easier to let your computer repair people do this for you, as they have lots of chips to experiment with.
TIP: Avoid performance issues by assuring that the speed of the RAM chip exactly matches that of the motherboard. For example, if you have a motherboard that supports the DDR 1333 standard, you should be sure to use RAM with that designation. (For your information, the 1333 is the memory’s transfer rate and not the actual speed of the memory.) Anything lower isn’t living up to the maximum you can expect from the RAM; anything higher and your processor may strain to keep up with it.
For information about FLASH RAM, which is a similar technology, click HERE.
FOR some time now, Windows (but not Linux, Unix and some other) computer systems have had a fundamental physical limit on how much RAM a given system can recognize. Most PCs today have a 32-bit internal architecture. This means that the computer can generate discreet memory addresses starting at zero up to a binary number (“0”s and “1”s) up to 32 digits in length. So, mathematically, this computes to 2 to the 32nd power, or a maximum of about 4.2 billion memory addresses total. Rounded off, this is about 4Gb.
For Windows 10, the Home, Pro, Enterprise or Education 32 bit versions are limited to 4Gb RAM, while the Home, 64 bit ias a 128Gb imit and the Pro, Enterprise and Education 64 bit versions support up to 512Gb of RAM.
That’s it. It’s a physical limitation that cannot be exceeded. You can put 6Gb of RAM into your 32-bit computer, but unless you have 64-bit architecture (providing up to 128Gb of RAM; that’s 16Eb [exabytes, or quintillion bytes]) using, for example, a 64-bit version of the Windows O/S or Linux, it’ll be useless. With those systems, you can add much, much more RAM.
Of course, you never actually have 4Gb of RAM available, even if you have that amount on your chips, because the system and possibly some of the cards consume much of this RAM before you even run any programs (see the discussion immediately below). Vista, for example, consumes upwards of 1Gb RAM just starting up!
And don’t forget that not every main board (particularly laptops) will necessarily support 4Gb of RAM - you’ll have to check with the manufacturer of the specific board.
[Not to confuse the issue, but under certain circumstances you can “fool” your system into believing it has more than 4Gb if you use virtual memory or something known as PAE technology if your version of Windows relies on another technology known as DEP. But this is a setting change for the pros, because it can cause other (driver and program) problems even when properly enabled.]
Now, just for edification for those of you who wonder why you purchased or installed 4Gb of RAM on your new Vista or Win7 32-bit computers and you only see 2Gb available, you should consider what I said above: Windows automatically manages up to 4Gb of RAM. Here’s what this means: Windows sees the additional RAM and, rather than just letting it sit doing nothing, it uses it to operate more efficiently, which is just what you want it to do. It sets aside about half the RAM as a place to store frequently accessed code and data for Windows and system related software, so that it relies less on the slower, hard drive based pagefiles for low level memory functions, making the whole operating system much more responsive. It still holds the rest of the RAM in reserve for user-initiated tasks such as loading applications and documents into memory. NOTE: This is precisely why those programs that promise to increase the available RAM on your computer are worthless, even dangerous. They can do this by removing code and data from the fast RAM back on to the slower hard drive RAM, actually working against you! (Thanks to Fred Langa, Windows Secrets for this explanation.)