Continuing memories
This week we will look at different types of Dynamic RAM (DRAM). As processors get faster, the need for memory to keep up with the pace of advancement and function more efficiently has been felt with increasing force. This has resulted in a rapid evolution of different RAM technologies over the years, resulting in considerable improvements in memory speeds, but in actual fact they are not much different from each other as the differences are mainly about how they are organized at the hardware level and accessed.

In a regular PC, most of the data requirements of the processor are satisfied by the primary or secondary cache memories of the processor and these often overshadow the improvements made on DRAM and their efficiency. But this in no way undermines the importance of the main memory which is critical towards overall system performance, even though it may help to keep in mind that memory is just one piece in the puzzle in overall performance. Often, ‘more system memory’ is more important to performance than ‘better system memory’ - more details on that later.

The most important factor that controls the type of memory that can be used in a motherboard is the system chipset. In fact, chipset support can be the difference between a technology being rapidly and universally accepted (e.g. EDO) and one lingering with little support and never becoming a popular standard (e.g. BEDO). The documentation for the motherboard will normally indicate what types of memory are supported by the board. In general, you want to use the fastest type of memory in the board that it supports, provided that it is not prohibitively expensive. Some people waste money buying memory that is a few percentage points faster than another type, when they could be improving performance more efficiently (such as buying more memory). Using too little RAM can be the biggest anchor dragging down overall system speed. This is something that many PC users fail to realize.

The amount of memory in the computer has no impact on the speed that the memory runs or on the speed that the processor, chipset, motherboard and other major system components run. However, that is if all of the programs running on the PC fit into the system RAM! All multitasking operating systems use virtual memory, which lets the PC think it has more memory than the actual physical RAM; the extra virtual memory is stored in a swap file on the hard disk. When more programmes and data are in use than physically fit in memory, the virtual memory manager swaps parts of memory to the hard disk, which is considerably slower than RAM.

Tip: Watch your hard disk LED. If you see it come on and flicker rapidly when switching between tasks for example, this probably means that your operating system is being forced to use virtual memory. If this happens often, it is a clue that you may need more memory. Next week will be a brand new chapter in our exploration of the different parts of the computer.

Improve your computer literacy
ASD Agent - Short for Automatic Skip Driver Agent, a utility in the Windows 98 and Me operating systems that monitors the loading of hardware drivers on a system and signals the user when there is a failure in one or more of the drivers that will prevent successful operation of the system.

ASD Agent will automatically disable problematic device drivers in order to ensure a successful startup, and the utility bypasses those drivers the next time the system boots unless the user indicates that the problematic driver be loaded at the next startup. Windows will automatically record the devices it disables in the Asd.log file.
Webopedia.com

Different Types of DRAM
Conventional DRAM - This is the oldest and slowest DRAM technology. It doesn’t require any special compatibility. This type of DRAM is now obsolete and is not used on new systems, having been replaced years ago by fast page mode memory and newer technologies.

Fast Page Mode - FPM memory is slightly faster than conventional DRAM. FPM memory itself is an improved version of its predecessor, page mode memory, which is very rarely seen now. Despite its name (‘fast’ page mode), FPM is actually the slowest memory technology used in modern PCs and offers lower performance than most other memory technologies.

Extended Data Out (EDO) DRAM - This was a very popular type of asynchronous DRAM. Sometimes it is also called hyper page mode DRAM and is slightly faster than FPM memory. In simplified terms, EDO memory has had its timing circuits modified so that one access to the memory can begin before the last one has finished. It is therefore slightly faster than FPM memory. EDO memory offers just a minimal speed increase over FPM memory. EDO memory also requires support from the system chipset.

Burst EDO or BEDO memory is another evolutionary improvement in conventional asynchronous RAM. In this case, EDO memory is combined with pipelining technology and special latches to allow for much faster access time than regular EDO. BEDO memory allowed for improved DRAM performance at very little additional manufacturing cost to the producer. In fact, BEDO provided more improvement over EDO than EDO did over FPM. Despite this, BEDO never caught on because of the very little real support it got.

Synchronous DRAM (SDRAM) - SDRAM differs from earlier types of memory in that it does not run asynchronously to the system clock the way older, conventional types of memory do. I will not go deeper into the workings of SDRAM since it can get very technical and confusing for the regular reader.

Double Data Rate SDRAM (DDR SDRAM) - Regular SDRAM was introduced as a proposed replacement for the older FPM and EDO asynchronous DRAM technologies due to the limitations the older memory had when working with systems using higher bus speeds (over 75 MHz). In the next couple of years, as system bus speeds increased further, the bell soon tolled on SDRAM itself. One of the proposed new standards to replace SDRAM is Double Data Rate SDRAM (DDR SDRAM). This is similar in function to regular SDRAM, but doubles the bandwidth of the memory by transferring data twice per cycle.

Direct Rambus DRAM (DRDRAM) - One of the two main competing standards to replace SDRAM was called Direct Rambus DRAM (DR DRAM). Unlike DDR SDRAM or SLDRAM (which are evolutionary designs based on regular SDRAM) DRDRAM was revolutionary in design. Although most of the industry agrees that Rambus is an inevitable stage in PC development, PC133 SDRAM is seen as a sensible evolutionary technology and one that offered a number of advantages.

DDR DRAM - Double Data Rate DRAM (DDR DRAM) was the other competing memory technology battling to provide system builders with a high-performance alternative to Direct RDRAM. As in standard SDRAM, DDR SDRAM is tied to the system’s Front Side Bus, the memory and bus executing instructions at the same time rather than one of them having to wait for the other. This has gained wide acceptance today.

Video RAM (VRAM) and Other Video DRAM Technologies - Modern video adapters use their own, specialized RAM that is separated from the main system memory. The demands placed on video memory are far greater than those placed on system memory. WRAM (Windows RAM) - Is similar to the VRAM, but even faster. Only in Matrox made graphics cards are used.

Multi-bank DRAM (MDRAM) - Simply the fastest RAM type, MDRAM which can handle over 1 Giga Bytes throughout may completely go out of production due to marketing issues.

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