All computers require memory to operate. The main computer memory is Random Access Memory, or RAM for short. It is called this because the data contained in it can be accessed in any, or random, order. It is produced on small circuit boards in the form of sticks, which are often referred to as sticks of memory. Information is stored in the memory as it awaits being processed by the central processing unit, or CPU. It is essential to have the right type and speed of memory to ensure your system is operating optimally.
The main type of memory used today in desktop computer systems is Synchronous Dynamic RAM (SDRAM). With in the past several years, Double Data Rate SDRAM (DDR SDRAM, or simply DDR) has become the standard for most systems, with older memory now being referred to as Single Data Rate (SDR SDRAM). Occasionally, systems use Rambus Dynamic RAM (RDRAM) or DDR2 RAM, which are slightly different and are outside of the scope of this article.
SDRAM is different from other forms of asynchronous memory because it waits for each clock, or computing cycle, before it responds to inputs. These clocks happen very fast in computers (millions of times a second) but still the speed of the memory is ultimately limited by the computer bus. This is the wiring on the main- or motherboard in the system that connects all the components. The processor and memory can both handle high clock speeds, but if the speed of the system bus is low, they will be limited by the lowest speed. It is important that they all operate at similar speeds to operate most efficiently. For example, SDR SDRAM comes in PC66, PC100 and PC133; these numbers refer to the clock speed of the RAM in megahertz (a million cycles a second): 66 MHz, 100 MHz and so forth. If the system bus speed is rated at 100 MHz and the memory at 66 MHz, then the memory isn’t operating as quickly as it could and PC100 memory should be purchased. Of course, if PC133 were purchased for this same system, the extra 33 MHz would simply be wasted because the system bus can only handle 100 MHz.
Double Data Rate (DDR) memory is very similar to traditional SDRAM except it transfers data twice during each clock cycle. This doubles the transfer rate of the memory while the system bus stays the same. So a 100 MHz system bus that handles DDR memory can effectively use 200 MHz RAM. DDR comes in many speeds, each with two designations. On the box or somewhere in the specifications, the memory will be referred to as DDR-xxx, where the xxx is replaced by the effective clock speed of the memory, such as 200 as in the previous example. It will also list a PC-xxxx number, where xxxx represents the bandwidth of the entire stick of memory. This is not particularly important to understand for novices. The most common are: DDR-200/PC-1600, which operates at a clock speed of 100 MHz (effectively 200 MHz), DDR-266/PC-2100, which operates at 133 MHz (effectively 266 MHz), DDR-333/PC-2700, operating at 166 MHz (333 MHz) and DDR-400/PC-3200, which operates at 200 MHz (400 MHz).
It is very important to know which type (SDR or DDR SDRAM) and speed of memory your system uses and to always purchase this type when upgrading or replacing your memory. You can usually find this information in the manual or contact the manufacturer.
Computer memory refers to either of two types of computer storage. Volatile memory refers to RAM that needs to be constantly refreshed to be retained. Static memory is permanent storage that is retained even after the computer is turned off.
RAM or Random Access Memory is volatile memory that is erased when the power goes off. Program instructions and data held in RAM can be accessed and saved much more quickly than that held in permanent storage. Therefore, files needed to run a program and data that is being processed are held in RAM while they are in use. The amount of RAM you need depends at least partly on the operating system( a program that directs all the basic functions of a computer such as accepting commands from a keyboard, displaying input on a monitor screen, and controlling disk drives and some other peripheral devices) you select as well as the type of programs you intend to run.
When you boot up the computer, in other words turn it on, the operating system or part of it is loaded into the RAM along with a variety of utilities required for normal operation. Therefore, programs and data are loaded into what’s left. As little as 2MB(megabytes) total will suffice for most DOS( disk operating system-a proprietary program that controls all the basic functions of a computer) programs. In a Windows 3.x environment, 4MB is the recommended minimum, but 8MB runs far better.
Beyond operating system demands, the amount of RAM required depends on the applications to be run. For example, heavy graphics, real time video, and such need more RAM to keep things from slowing to a crawl or stop. Generally, off-the-rack machines come with 8 to 16MB, more than enough for a general purpose computer.
With improved handling of memory, reduced access times, and lower cost have conspired to make larger amounts of RAM practical. Which in turn has given programmers free rein to add more bells and whistles. This also helps programmers to become more creative in writing programs that require more RAM. There is reason to believe that this trend will continue.
As for static memory, you don’t have to be very old to remember buying a computer without a hard drive, then later installing a 20MB hard drive, unable to imagine ever needing more storage than that. Today, a 250MB hard drive is popular; however, most new computers are in the 500 to 1000MB( 1 gigabyte) range. And you may need all of that MB and then some.
Computer Memory fact #1: For the faint of heart, when programs or data files are called up from permanent storage, they are not moved, they are merely copied. If the power goes off during processing, programs generally are safe. The only loss will be data that was changed since the last save.
Computer Memory fact #2: If you decided to get a MAC computer, don’t worry. The MAC computer comes loaded with a proprietary operating system and the proper amount of RAM to run it.
Volatile memory
Volatile memory is computer memory that requires power to maintain the stored information. Current semiconductor volatile memory technology is usually either static RAM (see SRAM) or dynamic RAM (see DRAM). Static RAM exhibits data remanence, but is still volatile, since all data is lost when memory is not powered. Whereas, dynamic RAM allows data to be leaked and disappear automatically without a refreshing. Upcoming volatile memory technologies that hope to replace or compete with SRAM and DRAM include Z-RAM, TTRAM and A-RAM.
Non-volatile memory
Non-volatile memory is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory (see ROM), flash memory, most types of magnetic computer storage devices (e.g. hard disks, floppy discs and magnetic tape), optical discs, and early computer storage methods such as paper tape and punch cards.Upcoming non-volatile memory technologies include FeRAM, CBRAM, PRAM, SONOS, RRAM, Racetrack memory, NRAM and Millipede.
