RAM

Random Access Memory, or RAM, is what the computer industry most commonly refers to as memory.  The main function of a RAM is to hold temporary instructions and data needed to complete tasks. With such a set-up, a computer's Central Processing Unit (CPU) can quickly access such instructions and data.

A command from the keyboard enables data to be copied from a storage device (a hard disk drive or a CD-ROM drive) into memory, which can provide data to the CPU more quickly than the storage devices.

Other than your processor's speed, the amount of RAM is the single most important factor affecting your system's performance. This is one instance where the amount matters more than the type.  Don't accept less than 32MB of RAM.   That's the minimum required if you want to switch to NT 5.0 later.  It is recommended to have 64MB RAM for NT 5.0 so you might as well get at least that much now especially since RAM is so cheap.  Windows 98 has a minimum RAM requirement of 16MB but it runs far better with at least 32MB.  Apps run better with the additional RAM.

Tests shows that an increase from 32MB to 64MB of RAM actually improves system throughput by as much as 10%.  While most test show no significant improvement in system performance throughput in the move from 64MB to 128MB, future apps and operating systems may benefit from 128MB of RAM.

As for RAM types, EDO RAM  is the faster of the older, Page Mode RAM  , but both of these use the same 72-pin SIMM slots. Synchronous Dynamic RAM (SDRAM) is faster than either, and uses yet another type of slot.  Go for SDRAM when possible. SDRAM is faster, and it will still be available years from now when the 72-pin SIMM's are a distant memory.   The next type of RAM will be Direct Rambus DRAM (DRDRAM), which will be packaged in Direct Rambus RIMM modules.  Direct RDRAM's should be considerably faster than SDRAM, and they will require yet another type of slot for their interface.  But because most calls for data come from the level 1 or level 2 caches anyway, the performance improvement wont be earth shattering..

Don't consider a PC that has no level 2 cache.  This means avoiding first-generation Celeron-powered PC's running at 266MHz or 300 MHz. Today's applications make heavy use of cache, and the first bit of cache is most important.  Most systems now come with 512KB of level 2 cache, but 256KB-or even 128KB as found in the second generation Celerons-help application performance immensely.  Some K6-2 systems come with a full 1 MB of level2 cache.

Windows NT 4.0 and other memory intensive 32 bit applications are very hard on memory - Many brands will fail /
freeze / lockup / give GP faults or damage data. If you are using or are planning to use these types of applications be very
selective with the memory you choose. The DRAM brands that tend to handle these applications include MICRON, Toshiba,
and Samsung (SEC).

Page Mode RAM  http://www.tomshardware.com/guides/ram/index3.html

EDO RAM  http://www.tomshardware.com/guides/ram/index5.html

SDRAM  http://www.tomshardware.com/guides/ram/index8.html

DRDRAM http://www.tomshardware.com/guides/ram/index13.html

IDENTIFYING YOUR MEMORY CHIP

1.  Chip Part Numbers

This section will help you decipher what the markings on your memory chips mean.    Memory chips are usually mounted on various kinds of modules, like SIMMs, which are designed to work in computer systems.  Often the memory module as a whole will have a part number, and the memory chips that are mounted on the module will have different part number(s).   The chip part number, along with the number of chips per module, allow us to determine the function and capacity of memory.

Memory chips tend to have 2 or 3 lines of text on them that include a part number, speed, and date code.  Most part numbers start with a two or three character abbreviation that identifies the manufacturer, such as HM (Hitachi), M5M (Mitsubishi), TMS (Texas Instruments) or MT (Micron Technology).

The numbers (and sometimes letters) that follow describe the memory configuration of the chip, for example HM514400 is a 1Mx4 configuration.

After the part number, there is usually a "A", "B", "C", or "D."   This is how some manufacturers grade the performance of the memory, with "A" being most superior and "D" least, e.g. HM514400A.    Manufacturers normally have very stringent requirements on all the memory they produce, so all grades should perform equally well in personal computers.    Also, be aware that some manufacturers, especially Micron and Texas Instruments whose part numbers almost always end in "DJ", do not use a letter to grade their parts.

In many cases, there will be an additional letter that codes the package type of the memory, e.g. HM514400AS.   In this example, "S" stands for SOJ-type packaging.

2.  Speed

Speed of the memory is an important factor that helps determine market value.    Carrying over from the previous example, a 70ns chip may be encoded at the end of the part number, e.g. HM514400AS7.   In this case, the "7" stands for 70ns.   Sometimes there is a dash before the speed marking, e.g. KM44C1000AJ-7, and other times the speed is printed on a line above or below the part number.   If the speed is printed on a separate line, a dash usually precedes the speed number.   For most common memory chips, speed ranges from 50ns to 200ns.   The trailing zero is commonly left off, so you may see "-6", "-7", "-8", "-10", or "-12", which represents 60ns, 70ns, 80ns, 100ns, and 120ns respectively.

On most chips, there is a date code printed above or below the part number.    The date code indicates when the chip was made, most typically in a year and week format (such as 9438 for the thirty-eighth week of 1994).   Often, the decade's "place" will be left off. For example, 438 may also represent the thirty-eighth week of 1994

Modules

The two most common types of memory modules are the 30 pin and 72 pin Single Inline Memory Modules or SIMMs.

The most common varieties of 30-pin SIMMs are 256kx8, 256kx9, 1Mx8, 1Mx9, 4Mx8 and 4Mx9 although 16Mx8 and 16Mx9 are also possible.  You will typically find either 2, 3, 4, 8, or 9 memory chips on 30-pin SIMMs.   Any given 30-pin SIMM is likely to be populated with identical memory chips, except the 3-chip SIMM. 3-chip SIMMs are likely to have 2 chips of the same type, and a third parity chip which is different from the other two.

The most common varieties of 72-pin SIMMs are 

 

4MB modules:1Mx32, 1Mx36
8MB modules: 2Mx32, 2Mx36
16MB modules: 4Mx32, 4Mx36

72-pin SIMMs that do not have parity (x32) usually have only one kind of chip per module.    For example, a 2Mx32 (8MB) can be constructed with 16 chips of 1Mx4 (such as a 424400-70). 72-pins with parity are likely to have two varieties of chips on board.    For example, a 1Mx36 usually has 8 chips of one type (1Mx4, like a 424400-70) and 4 chips of another (1Mx1, like a 421000-70).   When requesting a quote, it is important to note all the different chip part numbers on each SIMM, including parity chips.

Other SIMMs 

 
Less common simms include 40, 64, 68 and 80 pin SIMMs.   The 64 pin SIMM looks like a smaller 72 pin SIMM and is easily confused for one. Some 64 pin SIMMs function like 30 pin SIMMs while others function like 72 pin SIMMs.

SIPP or Single Inline Pin-leaded Package

Many older personal computers and workstations used SIPP memory, which look like SIMMs with pins instead of an edge connector.   This design was not as well received as the SIMMs because the pins tended to bend or break easily.