LESSON 1: INTERNAL AND EXTERNAL MEMORY TECHNOLOGY

Internal memory

Memory used directly or frequently during processing to store instructions and data needed by the CPU

Semiconductor memory

Memory bult from electronic semiconductor circuits that store data as binary values (Os and Is)

Memory cell

The basic storage unit that stores one bit.

Memory address

A location identifier used by the processor to locate specific data in memory

SRAM (Static RAM)

Memory that maintains its stored state While power is supplied and does not require periodic refreshing; commonly used for CPU cache

DRAM (Dynamic RAM)

Memory that stores each bit using a capacitor and transistor and must be refreshed regularly; commonly used as main memory.

Memory error

An unintended change in a stored bit, such as changing 0 to 1 or 1 to 0.

Error detection

The process of determining whether a memory error has occurred.

Error correction

The process of detecting an error and providing enough information to correct certain errors.

Parity bit

An extra bit added as a simple method for detecting some data errors.

ECC (Error-Correcting Code)

Check information used to detect and correct certain memory errors.

SEC-DED

Single Error Correction, Double Error Detection; a method that corrects a single-bit error and detects a two-bit error.

Memory bank

A subdivision of DRAM containing many rows and columns.

SDRAM (Synchronous DRAM)

DRAM that operates in synchronization with a clock signal.

DDR SDRAM (Double Data Rate SDRAM)

SDRAM that transfers data on both the rising and falling edges of the clock.

External memory / secondary storage

Nonvolatile storage used to keep information long-term, even when the computer is turned off.

Magnetic disk

A storage device that records data using magnetic patterns on a rotating disk.

Hard Disk Drive (HDD)

A magnetic storage device commonly used for large-capacity storage at relatively low cost.

Platter

A rotating disk coated with magnetic material inside an HDD.

Track

A circular path on a magnetic disk where data is stored.

Sector

A smaller division of a disk track used to organize data.

Read/write head

The HDD component that reads magnetic information and changes it when writing.

Actuator arm

The HDD component that moves the read/write head to the required track.

Seek time

The time needed to move the read/write head to the required track.

Rotational latency

The waiting time for the required sector to rotate into position under the read/write head.

Transfer time

The time required to move the actual data.

RAID (Redundant Array of Independent Disks)

A system that combines multiple physical drives into one logical storage system to improve performance, provide redundancy, or both.

Striping

A RAID technique that distributes data across multiple drives to improve performance.

Mirroring

A RAID technique that duplicates data across drives for greater reliability.

Parity

Extra information used in some RAID levels to provide protection against drive failure.

RAID 0

RAID level using striping for high performance, without redundancy.

RAID 1

RAID level using mirroring for data duplication and high reliability.

RAID 5

RAID level using striping and parity, providing protection against one drive failure.

RAID 6

RAID level using double parity, providing protection against two drive failures.

RAID 10

RAID level combining mirroring and striping for high performance and redundancy.

Optical memory

Storage that uses laser light to read and/or write information on optical discs.

CD

An optical disc typically holding about 700 MB, commonly used for music and small data files.

DVD

An optical disc typically holding about 4.7 GB on a single layer, commonly used for video and software.

Blu-ray

An optical disc typically holding about 25 GB on a single layer, used for high-definition video and larger data; it uses a blue-violet laser.

ROM

Optical-disc designation meaning read-only.

R

Optical-disc designation meaning recordable.

RW / RE

Optical-disc designations meaning rewritable.