Different types of RAM

RAM

RAM stands for Random Access Memory. It is place where computer stores its Operating System. Application Program and current data. when you refer to they mostly it mean RAM. The two main forms of modern RAM are Static RAM (SRAM) and Dynamic RAM (DRAM). DRAM memories (Dynamic Random Access Module), which are inexpensive . They are used essentially for the computer's main memory SRAM memories(Static Random Access Module), which are fast and costly. SRAM memories are used in particular for the processer's cache memory. Early memories existed in the form of chips called DIP (Dual Inline Package). Nowaday's memories generally exist in the form of modules, which are cards that can be plugged into connectors for this purpose. They are generally three types of RAM module they are

1. DIP

2. SIMM

3. DIMM

4. SDRAM

1. DIP(Dual In Line Package)

Older computer systems used DIP memory directely, either soldering it to the or placing it in sockets that had been soldered to the motherboard. Most memory chips are packaged into small plastic or ceramic packages called dual inline packages or DIPs . A DIP is a rectangular package with rows of pins running along its two longer edges. These are the small black boxes you see on , or other larger packaging styles. However , this arrangment caused many problems. Chips inserted into sockets suffered reliability problems as the chips would (over time) tend to work their way out of the sockets.

2. SIMM

A SIMM, or single in-line , is a type of memory module containing random access memory used in computers from the early 1980s to the late 1990s . It differs from a dual in-line memory module (DIMM), the most predomiant form of memory module today,in that the contacts on a SIMM are redundant on both sides of the module. Most early PC (8088-based PCs, XTs, and early ATs) used socket DIP chips. with the introduction of 286-based IBM XT/286, which could use larger amounts of memory , memory modules evolved to save motherboard space and to ease memory expansion. instead of plugging in eight or nine single DIP DRAM chips, only one addtional mmory module was needed to increase he memory of the computer. SIMM modules with 30 connectors (dimensions are 89x13m) are 8-bit memories with which first-generation PCs were equipped (286,386).

Single Inline Memory Module (SIMM) SIMM is a memory module with 72 or 30 pins, as shown in Figures and . SIMMs are considered legacy components and can be found in older machines. SIMMs with 72 pins can support 32-bit transfer rates and 32-pin SIMMs can support 16-bit transfer rates.

72 pin Bottom SIMMs

3. DIMM

A DIMM or dual in-line memory module, comprises a series of dynamic random access memory integrated circuits. These modules are mounted on a printed circuit board and designed for use in personal computers, and servers. DIMMs began to replace SIMMs (Single in-line memory modules) as the predominant type of memory module as -based Pentium processers began to gain market share. The main difference between SIMMS and DIMMs is that DIMs have separate electrical contacts on each side of the module, while the contacts on SIMMs on both sides are redundant. Another difference is that standard SIMMs have a 32-bit data path, while standard DIMMs have a 64-bit data path. Since Intel’s Pentium has a –bit width, it requires SIMMs installed in matched pairs in order to complete the data bus. The processer would then access the two SIMMs simultaneously. DIMMs were introduced to eliminate this practice.

4. SDRAM Synchronous dynamic random access memory (SDRAM) is a dynamic random access memory that is synchronized with the system bus. SDRAM has a synchronous interface, meaning that it waits for a clock signal before responding to control inputs and is therefore synchronized with the computer’s system bus.

Troubleshooting RAM Issues

RAM failures are either sudden or intermittent. Overused or defective memory can cause the system to fail at anytime. System performance is a good indication of the state of the memory. If the system is running smoothly and applications rarely stall, the RAM workload is well within the RAM specifications. If the computer is multitasking and frequently freezes, the RAM is probably insufficient for the workload.

Troubleshooting the RAM modules is straightforward. RAM is inexpensive and easy to replace. Technicians can easily remove the memory that is a suspected problem and add a valid module. If the problem is resolved, the RAM module is probably no longer operative. If the memory problem still exists, consult the motherboard documentation. Some motherboards require memory modules to be installed in a particular slot order, or require jumpers to be set. Figures , , and show the correct way to install SIMMs, DIMMs, and RIMMs.

Also, verify that the module has been correctly installed. Memory modules are notched and insert in one direction. If the user suspects an improper installation, remove the module and visually inspect the module socket. Remove any debris, dust, or dirt and reset the memory module.

Modern computers run software applications that are very memory intensive. These programs continually put stress on the memory modules, potentially causing them to fail. There are several common symptoms for failed memory:

• HIMEM.SYS has problems loading.

• Computer appears inoperative and does not boot.

• Windows program is unstable or programs are freezing.

• POST errors exist.

RAM Compatibility Issues

SDRAM memory modules come in various speeds. The most common SDRAM speeds are PC- 66, PC-100, and PC-133. The speed of SDRAM memory is measured in megahertz (MHz). SDRAM with a higher MHz rating indicates a higher performing memory module. SDRAM memory has compatibility issues with the bus on the motherboard. The speed of the SDRAM module must match the speed of the bus. Common bus speeds are PC-100 or PC-133. When looking to purchase RAM modules, verify the bus speed and buy a compatible RAM module.

The speed of EDO and FPM memory modules are measured in nanoseconds (ns). The memory module with the lowest ns rating is the fastest. EDO and FPM also have compatibility issues with the system bus.

Faster DRAM can be installed on a slower system bus and it will not affect performance. The system will operate at the bus speed even if faster memory is installed. However, a slower or mixed DRAM module cannot be installed on a system with faster DRAM requirements or different clocked DRAM.

Legacy machines might require parity RAM. Parity RAM performs error-checking calculations for every eighth bit of data stored. Today, RAM is non-parity and does not perform parity calculations on data. Never mix parity and non-parity SIMMs. For older systems, the setup utility has an option for enabling or disabling RAM parity checking. Also, error correction code (ECC) and non-ECC RAM cannot be mixed. ECC has the ability to correct data errors and is typically found in file servers. The following scenario helps to illustrate an issue with RAM.