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Memory

http://www.overclockingwiki.org/images/thumb/d/d3/RAM_n.jpg/300px-RAM_n.jpgMemory is referring to RAM, or Random Access Memory. RAM is a volatile type of computer data storage. RAM are integrated circuits which can be accessed “randomly” – the data stored on the chips is accessed in any order.

RAM is volatile – it loses the data stored on it when the computer is turned off – versus hard drive storage which is non-volatile, turn off the computer and the data isn’t lost.

RAM is used for storing the working area of the OS, applications, and data. RAM comes in memory “sticks” which insert into slots on the motherboard. RAM can be removed and upgraded very easily – and depending on the type of memory, could be upgraded a chip at a time. Other upgrade configurations include upgrading two chips at a time or four chips at a time.

As an IT technician, you will need to learn the differences between types of RAM and the technologies they use to ensure you properly upgrade or switch out memory in PCs.

A RAM module is the gum-pack size chip which plugs into the motherboard. On the RAM module, there are several memory chips.

 

DIMM Chips

A DIMM, or Dual Inline Memory Chip, is a major type of memory which is replacing SIMM, or single in-line memory modules. SIMMs have a 32-bit data path while DIMMs have a 64-bit data path. Most new chips have at least a 64-bit bus width, so it would require two “matched” SIMMs, versus a single 64-bit DIMM.

The most common types of DIMMs are:

  • 72-pin DIMM, used for FPM DRAM and EDO DRAM
  • 72-pin SO-DIMM, used for FPM DRAM and EDO DRAM
  • 100-pin DIMM, used for printer SDRAM
  • 144-pin SO-DIMM, used for SDR SDRAM
  • 168-pin DIMM, used for SDR SDRAM (less frequently for FPM/EDO DRAM in workstations/servers)
  • 184-pin DIMM, used for DDR SDRAM
  • 200-pin SO-DIMM, used for DDR SDRAM and DDR2 SDRAM
  • 240-pin DIMM, used for DDR2 SDRAM and FB-DIMM DRAM

For various technologies, there are certain bus and device clock frequencies that are standardized. There is also a decided nomenclature for each of these speeds for each type.

 

SDRAM DIMMs - These first synchronous registered DRAM DIMMs had the same bus frequency for data, address and control lines.

  • PC66 = 66 MHz
  • PC100 = 100 MHz
  • PC133 = 133 MHz

DDR SDRAM (DDR1) DIMMs - DIMMs based on Double Data Rate (DDR) DRAM have data but not the strobe at double the rate of the clock. This is achieved by clocking on both the rising and falling edge of the data strobes.

  • PC1600 = 200 MHz data & strobe / 100 MHz clock for address and control
  • PC2100 = 266 MHz data & strobe / 133 MHz clock for address and control
  • PC2700 = 333 MHz data & strobe / 166 MHz clock for address and control
  • PC3200 = 400 MHz data & strobe / 200 MHz clock for address and control

DDR2 SDRAM DIMMs - DIMMs based on Double Data Rate 2 (DDR2) DRAM also have data and data strobe frequencies at double the rate of the clock. This is achieved by clocking on both the rising and falling edge of the data strobes. The power consumption of DDR2 is significantly lower than DDR(1) at the same speed.

  • PC2-3200 = 400 MHz data & strobe / 200 MHz clock for address and control
  • PC2-4200 = 533 MHz data & strobe / 266 MHz clock for address and control
  • PC2-5300 = 667 MHz data & strobe / 333 MHz clock for address and control
  • PC2-6400 = 800 MHz data & strobe / 400 MHz clock for address and control

Chip speed data from: http://en.wikipedia.org/wiki/DIMM