Memory Technologies - CompTIA A+ 220-1201 - 3.3

Memory Technologies

Memory requirements vary by system. A home desktop may use standard memory, while servers and other systems running important services may use memory with error-detection or error-correction capabilities.

Parity Memory

• Parity memory stores an extra bit—the parity bit—alongside each 8-bit byte.
• With even parity, the parity bit is chosen so the total number of 1s in the byte and parity bit is even:
  • Six 1s → parity bit 0
  • One 1 → parity bit 1
  • Three 1s → parity bit 1
• When data is read, the system recalculates parity and compares it with the stored parity bit. A mismatch signals that an error occurred.
• Parity can detect some memory errors, but it cannot correct them and does not detect every possible error. A detected error may halt the system and require a reboot.

ECC Memory

• ECC means error-correcting code.
• ECC can detect and correct certain memory errors, allowing the system to continue operating normally.
• Standard, parity, and ECC memory modules may look very similar; their capabilities are identified by their specifications.

Memory Bandwidth and Multi-Channel Memory

• Memory bandwidth describes how quickly data moves between the CPU and memory, and affects system performance.
• Transfer rates are commonly stated in MT/s (million transfers per second).
• CPU and memory transfer speeds can become a bottleneck, causing the CPU to wait for data.
• Multi-channel memory increases throughput by giving the CPU multiple paths to communicate with memory modules simultaneously. Depending on motherboard support, systems may use dual-, triple-, or quad-channel configurations.
• For best compatibility and performance, modules used together should match—ideally in type, make, and model.
• Motherboards often color-code memory slots to indicate which slots should be populated together for multi-channel operation.
• Two modules can provide greater memory throughput than one module of the same combined capacity, such as two 16 GB modules rather than one 32 GB module.

Speaker / Source

• Professor Messer — instructor and narrator.