Install and Configure Memory

Install and Configure Memory
In the last topic, you installed a power supply. Providing sufficient electrical power is one way to ensure that system components run at an acceptable performance level, but it is not the only solution you should consider. In this topic, you will install and configure memory.
Just as some people say you can never be too rich or too thin, you can never have too much memory. Adding memory is one of the simplest and most cost effective ways to increase a computer’s performance, whether it’s on a brand-new system loaded with high-performance applications or an older system that performs a few basic tasks. One way or the other, upgrad- ing the memory is a frequent task for any computer service professional.
Memory Modules Definition:
A memory module is a printed circuit board that holds a group of memory chips that act as a single memory chip. Memory modules reside in slots on the system board, and they are removable and replaceable. Memory modules are defined by the number of chips they contain.

Memory Form Factors and Slot Types
Memory modules come in several form factors, and each module will connect to the system board through a memory slot of a compatible type.

Memory Form Factor
Single In-line Memory Module (SIMM)
Dual In-line Memory Mod- ule (DIMM)
Rambus Inline Memory Module (RIMM)
Memory Types

Description
Generally found in older systems, SIMMs have a 32-bit data path. Because most processors now have a 64-bit bus width, they required that SIMMs be installed in matched pairs so that the processor could access the two SIMMs simultaneously. SIMMs generally have 8 memory chips per module. Only SIMMs can be installed into SIMM slots on the system board.
DIMMs are found in many systems, and they have a 64-bit data path. The development of the DIMM solved the issue of having to install SIMMs in matched pairs. DIMMs also have separate electrical contacts on each side of the module, while the contacts on SIMMs on both sides are redundant. DIMMs generally have 16 or 32 chips per module. Only DIMMs can be installed into DIMM slots on the system board.
RIMMs have a metal cover that acts as a heat sink. Although they have the same number of pins, RIMMs have different pin settings and are not interchangeable with DIMMs and SDRAM. RIMMs can be installed only in RIMM slots on a system board.

Random Access Memory (RAM) is the main memory. The computer can both read the data stored in RAM and write different data into the same RAM. Any byte of data can be accessed without disturbing other data, so the computer has random access to the data in RAM. RAM is volatile and requires a constant source of electricity to keep track of the data it is storing. If the electricity is cut off, RAM forgets everything.
There are several types of RAM.

Type of RAM
SRAM
DRAM
DRDRAM SDRAM

Description
Static RAM is used for cache memory, which is high-speed memory that is directly accessible by the CPU. It does not need to be refreshed to retain information. It does not use assigned memory addresses. It is faster than Dynamic RAM, but it is also more expensive.
Dynamic RAM is used on single and dual in-line memory modules (SIMMs and DIMMs). It is the most common type of RAM. It needs to be refreshed every few milliseconds. Uses assigned memory addresses. Can be implemented using Synchronous DRAM, Direct Rambus DRAM, or Double Data Rate SDRAM.
Direct Rambus DRAM is implemented on a RIMM memory module.
Synchronous DRAM runs at high clock speeds and is synchronized with the CPU bus. SDRAM was originally packaged on a 168-pin DIMM.

Type of RAM
DDR SDRAM
DDR2 SDRAM
Sequential Access Memory (SAM)
RAM Speed

Description
Double Data Rate SDRAM transfers data twice per clock cycle. It is a replacement for SDRAM. DDR uses additional power and ground lines and is packaged on a 184-pin DIMM module.
DDR2 chips increase data rates over those of DDR chips. DDR2 mod- ules require 240-pin DIMM slots. Although DDR2 chips are the same length as DDR, they will not fit into DDR slots.
SAM is volatile memory that holds data in a sequential order. When accessing data, each storage cell is checked until the desired information is found. Often used for memory buffers where data is stored in the order it will be used.

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RAM speed is the time needed to read and recharge a memory cell. It’s measured in nanosec- onds (ns). A nanosecond is one-billionth of a second. The smaller the number, the faster the RAM. For example, 10 ns RAM is faster than 60 ns RAM.
RAM comes in ever-increasing speeds. The RAM on sale at the local computer store might work just fine in your system, or it might be older, slower RAM they are trying to move out of stock.
Older EDO RAM was often 60- to 70-ns speed RAM. Modern RAM that you are likely to find runs at clock speeds of 100 MHz and 133 MHz. The 100 MHz RAM has a RAM speed of 10 ns. The 133 MHz RAM has a RAM speed of 6 ns.

You need to check what RAM speed is currently installed. All of the RAM in the system runs at the lowest common speed. It is backward-compatible, so it can run at the lower speed if it finds slower RAM. Some systems will not run with mixed RAM speeds, but these are not common. Either way, the RAM will not run any faster than the system board’s bus speed.
DRAM Banks

You can combine multiple rows of DRAM into a cluster called a bank. Each row of DRAM can then be accessed simultaneously. When creating banks, the goal is to match the width of the DRAM to the width of the CPU’s external data bus, which will generally be 8-bit, 16-bit, 32-bit, or 64-bit. Expressed another way, the number of SIMMs or DIMMs needed to create a bank is the width of the CPU’s data bus divided by the width of the SIMM or DIMM. So, for a CPU with a 32-bit data bus, you need four SIMMs to create a bank.

Types of ROM
ROM is memory that is non-volatile. The original ROM chips could not be altered after the program code was placed on the ROM chip. As time went on, though, users needed the ability to update the information stored on ROM chips. Over the years, various chips have been cre- ated that perform the function of ROM, but can be updated one way or another. These are referred to as programmable ROM (PROM). Types of ROM include:

• ●  PROM: A blank ROM chip that is burned with a special ROM burner. This chip can be changed only once. After the instructions are burned in, it cannot be updated or changed.
  
• ●  EPROM (erasable PROM): Like PROM, except that the data can be erased through a quartz crystal on top of the chip. After removing the chip from the system, a UV light is used to change the binary data back to its original state, all 1s.
  
• ●  EEPROM (electronically erasable PROM): A chip that can be reprogrammed using soft- ware from the BIOS or chip manufacturer using a process called flashing. Also known as Flash ROM. The chip does not need to be removed in order to be reprogrammed.
  Memory Selection Tips
  There are several factors you should consider when purchasing RAM for a computer.
  

RAM Characteristics
Size
Speed
System Board Configuration

Questions to Ask
What is the maximum RAM size supported by the computer’s system board?
What is the current speed of the RAM in the com- puter? What is the bus speed of the computer?
Do you need to install RAM in pairs of memory modules? What is the size of the connector for RAM chips?

How to Install and Configure Memory Procedure Reference: Add RAM to a Computer
To add RAM to a computer:

1. Review the computer’s current configuration to make sure that the computer’s memory slots aren’t already full.
   
2. Determine how much RAM is currently installed so that you can determine afterwards if the new RAM you installed is recognized. You can check the CMOS settings or use the System Properties dialog box in Windows XP to verify the amount of RAM.
   To check the RAM through System Properties:
   
   1. From the Start menu, choose My Computer.
      
   2. In the System Tasks box on the left side of the window, click View System Information.
      
3. Shut down your computer and disconnect the power cord. Press and hold the power but- ton down for 10–30 seconds to release any stored energy in the system.
   
4. Discharge any static electricity from yourself or your clothes. Although this is always important to do, it is especially important to do when working with memory cards. These components are more delicate and more easily damaged by static charges than other sys- tem components.
   
5. Locate an empty memory expansion socket on the system board, or, if there are no empty slots, remove a smaller memory module to make room for one containing more memory.
   To remove an existing memory module:
   
   1. Press down on the ejection tabs.
      
   2. Firmly grasp the memory module and pull it out of the slot.
      
6. Align the notches in the connector edge of the memory module with the notches in the memory expansion socket, and then firmly press the memory module down into the socket.
   
7. If the ejection tabs did not lock into the notches on the ends of the memory module, push them up until they lock.
   
8. Restart the computer.
   
9. Follow any on-screen prompts or perform any steps described in your computer’s docu- mentation for getting the computer to recognize additional memory. This is not required on all computers.