PC memory guide

Random access memory (RAM) is the main memory of your pc. Memory allows temporary data storage and access, at a very fast speed. This memory is used as temporary storage by your pc, and by the software that you are running, during the day to day running of your pc. Memory modules are small thin circuit boards of small semiconductor chips that can be slotted into the motherboard. Memory can also be easily upgraded, and increased to help increase the performance of your PC. If you find that your pc is taking ages to load things up, its probably because you don't have enough memory. Saying that though, if you had all the memory in the world installed on your pc, you would still find some way of complaining that your pc is still running slow. Memory is the main ingredient in the ease at which we can shift between multiple programs and multiple windows, or internet pages.

Memory Compatability

Not all memory modules work with every motherboard, and so there are 2 methods for your pc to check if they are suitable.

Parity RAM

Parity RAM uses a parity checking method to check that the integrity of the digital data stored in the memory by detecting any errors. Memory modules that use parity checking are called parity RAM. The modules are not really used in today's motherboard designs.. A single parity bit is used as the error-detecting code. The parity bit is a binary digit (0 or 1) which indicates if the total number of bits that have a value of 1 in any given set is even or odd. The Two types of parity bits that are used are the even parity bit and odd parity bit. The even parity bit is always set to 0 when the total number of 1s in the given group is even. If the total count of the 1s is odd, then the bit is changed to 1.

The odd parity bit is changed to 0 when the total number of 1s in the given set is odd. If the total number of 1s is odd, and the bit is set to 0. Parity checking is only a useful method for checking errors. It won't in any way help you to fix the problem, or even notify you of it..

Error Checking and Correction RAM (ECC RAM)

ECC RAM automatically detects and also corrects any errors in the memory. It does this without bothering the motherboard. The ECC mechanism creates checksums before storing the data in its memory. When the data is retrieved from your pc's memory, the checksum is calculated again to decide if any of the data bits have been corrupted in anyway. ECC memory will generally detect 1-bit and 2-bit errors, but can only fix errors that are 1 bit per word.

Types of Memory

Computer RAM can be either a dynamic or static state. For most of the common pc functions, the dynamic random access memory (DRAM) is used as the main memory of the pc, and the static random access memory (SRAM) is used for the system cache.

DRAM

DRAM stands for dynamic random access memory. Dynamic refers to the requirement of the pc memory chip to be occasionally refreshed in order to maintain its contents. If this check fails, the stored contents of the DRAM can be lost. DRAM memory is much cheaper than the other types of memory available, and it is the most common used to expand the memory of a pc. There are variations of DRAM memory and they include SDRAM, DDR, DDR2, and RAMBUS.

SDRAM

SDRAM stands for synchronous dynamic random access memory. SDRAM memory has a synchronous interface. This is when the memory waits for a clocksignal before it responds to any input. SDRAM is synchronized with the computer’s CPU and the system bus. SDRAM interfaces between the CPU in a parallel 8-byte (64-bit) bus and thus, a 100 MHz clocksignal produces 800 MBps throughput. The 100 MHz SDRAM modules are called PC100 chips.

DDR SDRAM

DDR SDRAM also called: double data rate synchronous dynamic random access memory. This type of memory module can double the data transfer rate by using both the rising and falling edges of the clock rate, without increasing the frequency of the PC's system bus. This means that 100 MHz DDR memory has an effective clockrate of 200 MHz. For a 100 MHz clock signal, the data rate becomes 1600 MBps (2 × 8 × 100). DDR SDRAM modules are also called PC1600 chips.

DDR2 SDRAM

DDR2 SDRAM or double data rate 2 synchronous dynamic random access memory. This type of PC memory first doubles the clock rate by using both of the edges of the clock signal and then splits a single clock into two. This means that it doubles the number of operations in each clock cycle. DDR2 SDRAM has a lower power consumption, and uses 1.8 volts, compared to 2.5 volts used by DDR SDRAM. DDR2 modules are also called DDR2-400 or PC2-3200 chips.

DRDRAM

DRDRAM or Direct Rambus dynamic random access memory. This is a type of memory developed by the Rambus Corporation. This memory module is no longer commonly in use. DRDRAM supports the PC800 standard and operates at 400 MHz The effective data transfer rate is 1600 MBps on a 2 byte (16-bit) data bus

SRAM

SRAM or static random access memory. This type of memory, which features static capabilities means that the contents of the memory are stored as long as the power is kept on. SRAM is faster and also more expensive than DRAM. It is mainly used for the important job of cache memory.

SIMM

SIMM or single inline memory module. This type of memory comes in two main types: 30-pin, which has 8-bit data bus, and also 72-pin, which has 32-bit data bus. SIMMs don't have the standard pin configuration,and have been mostly replaced by DIMM.

DIMM

DIMM or dual inline memory module. DIMM is a 64-bit memory module which is used for SDRAM, DDR, and DDR2 memory. The standard SDRAM has 84-pins on both sides, making it a 168-pin module. DDR DIMM has 184 pins with 1 notch, and DDR2 DIMM memory module has 240 pins with 1 notch. The DDR2 DIMM also has an aluminum cover on both of the sides as a heat sink to prevent overheating.

RIMM

RIMM or Rambus inline memory module. This is a type of custom memory module made by Rambus. RIMM memory modules come in a 16-bit single channel width or in 32-bit dual channel bus width. The 16-bit memory modules have 184 pins, and the 32-bit memory modules have 232 pins. Sixteen-bit memory modules require pairs of slots on the motherboard, while the 32-bit memory modules only need one. RIMM memory normally has an aluminum cover to help protect against overheating.

SO-DIMM

SO-DIMM or small outline dual inline memory module. This type of memory is mainly used in laptop computers. The older 32-bit SO-DIMM memory module had 72 pins, while the newer 64-bit memory modules are available in 144-pin and 200-pin configurations.

Micro DIMM

Micro DIMM is the very smallest of all the DIMM memory module types. Its about half the size of a SO-DIMM memory module. Again, mostly used in laptop computers. Micro DIMM modules have a 64-bit bus width and are available in 144-pin or 172-pin configurations.

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