Installing and configuring system memory

Question 1

System RAM

Answer 1

When a process is executed or a data file opened, the image is loaded from the fixed disk into system memory. Instructions are fetched from system memory and into the CPU’s cache and registers as required.

System memory is implemented as random-access memory (RAM) devices. RAM is faster than the flash memory used for SSDs and much faster than an HDD, but it is volatile.

The amount of system RAM determines the PC’s ability to work with multiple applications at the same time and to process large files efficiently.

Question 2

Virtual RAM/Virtual Memory

Answer 2

If there is not enough system RAM, the memory space can be extended by using disk storage. This is referred to as a pagefile or swap space. The total amount of addressable memory (system RAM plus swap space) is referred to as virtual memory or virtual RAM .

Question 3

Address Space

Answer 3

The width of the data pathway determines how much information can be transferred per clock cycle. In a single channel memory controller configuration, the data bus is usually 64 bits wide.
The width of the address bus determines how many memory locations the CPU can keep track of and consequently limits to the maximum possible amount of physical and virtual memory.

Question 4

RAM Types

Answer 4

Modern system RAM is implemented as a type called Double Data Rate Synchronous Dynamic Random Access Memory (DDR SDRAM).

Dynamic RAM stores each data bit as an electrical charge within a single bit cell. A bit cell consists of a capacitor to hold a charge (the cell represents 1 if there is a charge and 0 if there is not) and a transistor to read the contents of the capacitor.
Synchronous DRAM (SDRAM) is so-called because its speed is synchronized to the motherboard system clock.
Double Data Rate SDRAM (DDR SDRAM) makes two data transfers per clock cycle.

Question 5

Memory Modules

Answer 5

A memory module is a printed circuit board that holds a group of RAM devices that act as a single unit.

DDR for desktop system memory is packaged in a form factor called dual inline memory module (DIMM). The notches (keys) on the module’s edge connector identify the DDR generation (DDR3/DDR4/DDR5) and prevent it from being inserted into an incompatible slot or inserted the wrong way around.

For best performance, the modules should be rated at the same bus speed as the motherboard. Laptop RAM is packaged in a smaller form factor called Small Outline DIMM (SODIMM)

Question 6

Multi-Channel System Memory

Answer 6

Single-channel memory means that there is one 64-bit data bus between the CPU, memory controller, and RAM devices. With a dual-channel memory controller, there are effectively two 64-bit pathways through the bus to the CPU, meaning that 128 bits of data can be sent per transfer rather than 64 bits.

When configuring a dual-channel system, you will need to consult the system documentation to identify the appropriate slots to use. Dual-channel mode may also need to be enabled via the PC firmware’s system setup program.

Question 7

ECC RAM

Answer 7

Error correcting code (ECC) RAM is used for workstations and servers that require a high level of reliability.

This system can detect and correct single-bit errors and allow the PC to continue functioning normally. ECC can also detect errors of 2, 3, or 4 bits but cannot correct them. Instead, it will generate an error message and halt the system.

Most types of ECC are supplied as registered DIMMs (RDIMMs). A registered DIMM uses an extra component to reduce electrical load on the memory controller.
Most types of non-ECC memory are unbuffered DIMMs (UDIMMs).

Both the motherboard and CPU must support ECC operation for it to be enabled.
Mixing non-ECC UDIMMs and ECC UDIMMs is unlikely to work.