RAM Types | CompTIA A+ 220-1001 | 3.3

In this video you are going to learn about RAM types, single, dual & triple channels, parity vs. non-parity bits, and error correcting code.

Purpose of RAM

Random Access Memory is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code. RAM allows data items to be read or written in almost the same amount of time irrespective of the physical location of data inside the memory. In contrast with other direct-access data storage media such as HDDs, CDs, DVDs, & older magnetic tapes and drum memory, the time required to read/write data items varies significantly depending on their physical location on the recording medium, due to mechanical limitations such as media rotation speeds and arm movement.

In today’s technology, RAM takes the form of integrated circuit (IC) chips with MOS (metal-oxide-semiconductor) memory cells. RAM is normally associated with volatile types of memory, where stored information is lost if power is removed, although non-volatile RAM has also been developed.

RAM Review

SODIMM & DIMM Memory

Small Outline Dual Inline Memory Module (SODIMM) is a type of computer memory built using integrated circuits. SODIMMs are a smaller alternative to a DIMM, being roughly half the size of regular DIMMs, where they are utilized in laptops due to the compressed form factor of laptops in comparison to that of desktops.

DIMM vs. SODIMM

DDR2 SDRAM

Double Data Rate 2 Synchronous Dynamic Random Access Memory is the successor to DDR SDRAM (SDRAM runs faster than conventional memory). It offers new features, greater bandwidth (more data can be passed through the RAM chip at one time) and lesser power consumption than its predecessor. Like standard DDR memory, DDR2 memory can send data on both the rising and falling edges of the processor’s clock cycles. This nearly doubles the amount of work the RAM can do in a given amount of time.

DDR3 SDRAM

DDR3 SDRAM is available in both DIMM & SODIMM form factors. DDR3 SDRAM is similar to DDR2, but uses approximately 30% less power and can transfer data twice as fast. DDR3 supports a maximum data transfer rate of 6400 MBps (megabytes per second) while DDR2 supports up to 3200 MBps. The faster memory speed prevents data transfer bottlenecks when it comes to processing large amounts of data.

DDR4 SDRAM:  The Current Standard

DDR4 SDRAM is the fourth generation of DDR RAM designed to replace DDR3. The advantages of DDR4 include faster data transfer rates and larger capacities due to greater memory density in addition to more memory banks (16 rather than 8). DDR4 also operates at a lower voltage (1.2V compared to 1.5V) making it more power-efficient. Some notable DDR4 specifications are:

  • 64GB maximum capacity per memory module (common capacities include 16GB and 32GB)
  • 16 internal memory banks
  • 1600 MBps to 3200 MBps data transfer rates
  • 1.2 volts of electrical power required
  • 288 pins in a regular DIMM, 260 pins in a SODIMM
DDR SDRAM Key Notch Placement

Single Channel

Single channel RAM operates on a 64-bit data channel which means that it can push 64 bits of data down the pipe that is 64-bits in total length.

Single Channel RAM

Dual Channel

When it comes to adopting the multi-channel configuration, this means multiplying the effective channel width by the total count of available channels. When two identical (same size, speed, and latency) modules are installed in the proper sockets, the memory controller accesses them in interleaved mode for faster access.  This is why almost all RAM upgrades are done in pairs of chips. The majority of systems with two pair of sockets in contrasting colors implement dual-channel operation.  Install the matching modules in the same color sockets.

Dual Channel RAM
Memory Socket Used for Dual Channel Operation

Triple Channel

Triple-channel RAM is designed to triple the speed of the RAM bandwidth.  Some triple-channel motherboards use four sockets, but for best performance, the last socket should not be used on these systems. One thing to remember about single, dual, & triple channel memory is that the chips are not different for each. The only difference is in the way the motherboard accesses the chips.

Parity vs. Non-Parity

As data moves through computers, the possibility of errors can occur. Parity error detection was developed to notify the user of any data errors by adding a single bit to each byte of data which is responsible for checking the integrity of the other 8 bits while the byte is moved or stored. Once a single-bit error is detected, the user receives an error notification. However, parity checking only notifies and does not correct a failed data bit. Some system error messages will tell you the logical location of the error so you can reference system documentation to determine which module or modules to replace. Non-parity is memory chips that do not have a ninth bit used for parity checking.

Error Correction Code (ECC)

In computing, an error correction code is used for controlling errors in data over unreliable or noisy communication channels. The central idea is the sender encodes the message with redundant information in the form of an ECC. The redundancy allows the receiver to detect a limited number of errors that may occur anywhere in the message, and often to correct these errors without retransmission. Most desktops do not support ECC, although some workstations & most server do offer ECC support. Memory that uses ECC enables the system to correct single-bit errors and notify you of large errors. Systems that offer ECC support may be enabled or disabled via the system BIOS, or it might be a standard feature. The parity bit in parity memory is used by the ECC feature to determine when the content of memory is corrupt and to fix single-bit errors.  Unlike parity checking, which only warns you of memory errors, ECC memory actually corrects errors.