All About Ram "Random Access Memory"

Q: What do the acronyms DRAM, EDO RAM and SDRAM mean, and how does each type of RAM differ?

A: DRAM stands for dynamic random access memory. As this type of memory requires a constant current to retain information, it needs to be refreshed hundreds of times per second. The memory uses the same circuit to store and retrieve data, so access times can be an issue. Memory is organized in pages, and when one page is accessed, it takes additional CPU cycles to switch to another page to access more memory.

EDO RAM stands for extended data out RAM. It's similar to DRAM, but EDO RAM operates between 10 and 15 percent faster because it starts accessing the next block of data while sending the previous block to the CPU. That makes it easier and quicker to synchronize data transfer than with regular RAM. EDO RAM is used in both SIMMs and DIMMs (see the next question), while regular DRAM is typically found only on PCs with SIMMs.

SDRAM stands for synchronized DRAM. It is significantly different from regular DRAM because it uses a clock cycle timing for data access and refresh. It operates at the same frequency as the system bus and synchronizes automatically with requests from the CPU. That makes it faster than DRAM and EDO RAM. SDRAM is typically found only in DIMMs.

Q: What is the difference between SIMMs and DIMMs? And what are RIMMs?

A: SIMM stands for single in-line memory module; DIMM stands for dual in-line memory module.

RAM chips are typically packaged in 8MB, 16MB, 32MB or 64MB modules that plug into a PC's motherboard. These modules are small, standard-size circuit boards that hold the actual RAM chips. Memory used to come in 30-pin SIMMs, but now you'll find these SIMMs only on older PCs. Pentium-based PCs have the newer 72-pin SIMMs-which hold more memory and can access it better-or the newest DIMMs. DIMMS can hold even more memory and typically have 84 pins active on both sides for 168 connections.

While unbuffered DIMMs are limited to 64MB, newly designed registered DIMMS can hold 128MB or 526MB. These registered DIMMs are found in servers and high-end workstations.

RIMMs, or Rambus memory modules, will be used with Intel's next-generation Rambus memory interface, which will support high-speed buses and provide much greater bandwidth than current memory (more on Rambus below).

Q: Does the speed of my RAM matter?

A: The newer the system, the more RAM speed matters. On older systems with SIMMs, speed matters less. A 60-nanosecond DRAM should work fine for all PCs, and some older systems can run on slower speeds of 70ns or 80ns.

SDRAM speed is measured in MHz because it is clocked, just like the system bus. Newer systems based on Intel's Deschutes Pentium II processors use a 100MHz system bus and require memory clocked at that speed. If your system uses EDO or SDRAM, make sure your RAM conforms exactly to the manufacturer's specifications. If you upgrade or replace RAM on a PC with DIMMs, you need to follow exact instructions in your system manual.

Q: Can I use my existing RAM in a new PC when I upgrade?

A: If your new PC has a system bus clocked at 66MHz or slower, and the PC uses a compatible memory module (SIMMs or DIMMs), then it is possible. Some systems are designed to take a mixture of SDRAM, EDO RAM and even DRAM, but many require a particular type of memory. You should check the precise specifications of your new machine.

If your new PC has a 100MHz system bus, you can't use the old RAM (unless your old system had a 100MHz system bus). Make sure the RAM in the new machine is designed to run at 100MHz, or else you'll see slower performance and even memory page faults that could crash the system.

Q: Is RAM for notebooks the same as RAM for desktop PCs?

A: Notebook memory chips are typically the same types of RAM as used in desktop PCs, but with different packaging. Many notebooks use smaller SODIMMs (small-outline DIMMs). These come in 72-pin and 144-pin modules. But many notebook manufacturers use proprietary memory modules, so if you want to expand RAM, you have to get memory designed specifically for that machine.

Q: Is the RAM on a graphics card the same as regular system RAM?

A: Graphics cards have special requirements because they must simultaneously move data rapidly into and out of graphics memory to the display. Therefore, most graphics memory is dual-ported, meaning it can send and receive data simultaneously. Graphics memory types include VRAM (video RAM), TPRAM (triple-port RAM), SGRAM (synchronous graphics RAM). Most current cards use SGRAM.

Q: What's cache memory? Can I upgrade it?

A: Cache memory is temporarily held data that's immediately ready to use, speeding up your system. The Intel Pentium and many other CPUs have this memory built right into the processor. That's level 1 cache, and you can't change it. Most CPUs now also have level 2 cache, used by the main system RAM. Cache memory is much faster than regular RAM.

Static RAM is a type of cache memory that usually requires no refreshing or synchronizing and returns information to the CPU virtually instantly. You can only upgrade cache memory if your system's cache memory socket is accessible and includes a larger secondary cache as an option. If your system has a Pentium II, you have to replace the entire processor to upgrade the cache because the system cache is inside the processor's housing.

Q: What about future developments?

A: As CPU speeds increase, memory must become faster to avoid bottlenecks. Two types of faster RAM are currently proposed. Intel is backing Rambus or RDRAM, a much more complex type of memory interface using a special 800MHz bus and a protocol- and packet-based system for transferring data. Because Intel plans to eventually double the bus speed to 1.6GHz, Rambus is also likely to be the fastest of the proposed suggestions.

A cheaper alternative is high performance SDRAM-DDR, or double-data rate SDRAM. SDRAM-DDR reads data at 200MHz, twice the 100MHz speed of current high-end PC buses. An advanced version of this, SLDRAM (SyncLink DRAM) will quadruple the data rate to 400MHz. The latter two alternatives are cheaper and easier to implement than Rambus. We may see Rambus in high-end PCs and SLDRAM in less-expensive systems.

None of the existing RAM solutions will transfer upward to these new systems. The RAM you're using today isn't likely to work in the PCs of tomorrow.

Sites to Be Seen Check out these Web sites for more information on RAM.

http://www.corsairmicro.com/sdramfaq.htm
Corsair Memory answers Frequently Asked Questions about SDRAM.

http://www.kingston.com
Kingston Technology, the largest memory retailer, offers information, advice and products.

http://www.buymemory.com
Memory dealers McDonald and Associates' site includes more explanation than most about what you may or may not be buying.

http://pcmech.pair.com/mbindex.htm
PC Mechanic's memory Web site offers RAM installation tips and information.

http://www.rambus.com
Rambus Online contains information about Rambus memory.

http://www.tomshardware.com/ram.html
Tom's Hardware Guide's RAM Guide gives technical details of all types of RAM.

http://www.sldram.com/home.html
The SLDRAM not-for-profit corporation's page includes information on all you need to know about SyncLink DRAM.

I wrote http://www.winmag.com and asked if I may post an article or two from their site. They graciously obliged me saying it was alright as long as I provided a link to their site.
This was written by Owen Linderholm

Memory, Virtual Memory Management FAQ

Don't mix different memory types

What you need to know about RAM

What you need to know about the types of memory

What you need to know about memory modules

What you need to know about parity in memory chips

What you need to know about pin size in memory chips

How much memory do you need?

What you need to know about computer, printer and graphics RAM

How do you partition a Mac disk on an IDE drive?

Buyer's Checklist: Desktop Systems -- Memory

Buyer's Checklist: Server Memory

Why does my 2.5 GB hard drive give me error messages claiming "insufficient memory?"

What do the terms used to describe memory modules mean?

How much RAM does my system need if I run high-end graphics programs?

Can I mix EDO and non-EDO RAM in my Pentium P90 system?

How important is it that memory connector metals match?

How are RAM disks used most effectively?

Why do I get a warning that there is "under 500K of disk space" on my start up volume?

Can I install EDO on an older system and have it remain compatible?

I get a boot error message that goes away as the machine warms. What's happening?

Is there any way to combine several older SIMMs into a unit that ocuppies only one slot?

I have a bunch of old SIMMs. How can I tell what size they are?

What is the difference between 9-chip and 3-chip 30-pin SIMMs?

What are the differences in how DOS and Windows handle memory? Microsoft DOS

Can I upgrade my system with RAM rated at a different speed than the original chips? Intel 486

How can I get rid of the RAM Disk on my desktop?

Where is all the RAM going on my system? It appears to be running at full-speed.

Is Sdram the fastest memory available?

What does the writing on RAM chips mean? How can I tell what the chips are?

Can I replace 9 chip memory with 3 chip memory or mix the two on the motherboard?

How do I install RAM upgrade?

How Do I Add Memory to a 386 PC? Intel 386

How do I make my ram recognizable?

Why Won't All My New RAM Show Up?

Why do I keep getting 'not enough memory' error messages?

Why do I get "memory test fail" error messages when I start up?

Why isn't my computer faster after installing an additional 16MB of RAM?

Why Doesn't My PC Run?

With SDRAM, Do We Still Need L2 Cache?

Do I Need to Add Memory?

Can I Mix Memory Types?

Why Can't My PC Work WIth All Its RAM?

Will increasing my PC's RAM increase my Internet access speeds?

Is parity memory better than non-parity memory?

Choose 30-pin SIMMs when upgrading memory for a 486 machine.

Why Won't My PC See All The New Memory?

Avoid Mixing Tin And Gold Connections

Mix 'n' Match EDO and Non-EDO Memory?

RAM: Too Much of a Good Thing?

RAM Conspiracy Exposed!

100MHz or Busted

Things to Come: Part 1

What's the difference between Fast Page RAM and EDO RAM?

Can I change the sockets in my PC so I can use cheaper RAM?

What's the difference between SDRAM and EDO DRAM?

How much RAM is too much?

How do I add memory to my computer?

First Things First: Upgrade Your RAM

Faulty RAM chips can be the source of frustrating system crashes. Microsoft Windows 98

I have the option to have SDRAM or ECC RAM with my PC. Is it worth it to add on?

Can I just buy any size/brand RAM, or does it have to be compatible with my computer?

Memory Musing

Too Much Memory?

Let's Take a Look At Rambus

Short for Rambus DRAM, a type of memory (DRAM) developed by Rambus, Inc. Whereas the fastest current memory technologies used by PCs (SDRAM) can deliver data at a maximum speed of about 100 MHz, RDRAM transfers data at up to 600 MHz.

In 1997, Intel announced that it would license the Rambus technology for use on its future motherboards, thus making it the likely de facto standard for memory architectures. However, a consortium of computer vendors is working on an alternative memory architecture called SyncLink DRAM (SLDRAM).

RDRAM is already being used in place of VRAM in some graphics accelerator boards, but it is not expected to be used for the main memory of PCs until 1998 or 1999. Intel and Rambus are also working a new version of RDRAM, called nDRAM, that will support data transfer speeds at up to 1,600 MHz.

So, do you just go out and but yourself some Rambus modules and stick them into your system.
Well, it's not quite that simple:
See:
Sandra Underhill's "First look at the all new Super Fast 800MHz Memory and the system changes needed to accomodate it."
http://www.infinisource.com/features/rambus800.html

Rambus Home Page
http://www.rambus.com/
Corporate web site for Rambus, Inc., developer of Rambus DRAM.

Synchronous DRAM (SDRAM)
http://www.pcguide.com/ref/ram/tech_SDRAM.htm
Excellent overview of SDRAM, along with details on RDRAM and VRAM memory and technologies. This page is from "The PC Guide".

Dvorak on RDRAM and SLDRAM
http://www.pcguide.com/ref/ram/tech_SDRAM.htm
John C. Dvorak muses on the strategic motivations behind Intel's backing of RDRAM.
Personally, I think this guy is very negative.

SDRAM vs. RDRAM, Facts and Fantasy
http://www.hardwarecentral.com/hardwarecentral/reviews/1787/1/
In-depth analysis of Rambus' RDRAM aims to find its technological advantages and disadvantages, as well as reach a verdict on the SDRAM vs. RDRAM issue.

7Search Com's Rambus Pages.
http://7search.com/scripts/search.asp?qu=rambus&Language
=1&Filter=on&Affiliate=28464

What Does Ram Do?

RAM (Random Access Memory) is short-term memory like in your head. It is fast and readily at hand to be used by your computer, however not permanently there. The long-term stuff the computer uses is on the hard drive.

When the brain (processor) needs information it will only ask RAM for it because it is quicker. If you had to ask the hard drive for everything you would wait a long time to do the simplest task. Here is how it works:

RAM is divided into "pages" and when the processor requests a file from the hard drive it is sent to RAM. It takes up as many pages as it needs to provide fast access to the information. The information will remain there until no more pages are available for RAM to use. So what happens then?

RAM is great at juggling. If all available pages are being used RAM will use a folder on the hard drive to store the least used pages temporarily. This makes space for the latest requested ones. This is known as "swapping" and is used to make the most needed information available as fast as possible. But what if I need a file that was swapped to this temporary folder, again?

The same thing happens all over; the least used pages in RAM are swapped for the ones you want. Once you decide you are done with the file it can be saved (not swapped) back to hard disk in its original spot.

Why is this important? Too much of this swapping makes for a slower computer overall and wears out your hard drive in a shorter period of time. The telltale signs of too much swapping is constant spinning of the hard drive and slower than usual response. How do you fix it? Add RAM. You can never have too much of a good thing.