1.2 Memory and Storage

where data and instructions are stored so they can be accessed directly by the CPU

used to permanently store data such as the operating system and user’s files

holds all of the data and instructions that are currently being processed.

Inside the RAM, memory is split up into separate locations, each with a unique memory address. The processor uses these addresses to access data stored in RAM.

Power is required to hold the data.

typically used to store the boot sequence (BIOS) for a computer.

will not lose its data when the power is switched off.

stored on ROM. It is a limited sequence of instructions which checks that the core components of the computer system (RAM, fundamental input/output devices, secondary storage) are connected and responding correctly.

When a system requires virtual memory, the operating system creates a set of virtual addresses. (RAM is separated into a set of physical addresses.) Data moved to virtual memory is stored as pages.

used when there simply isn’t enough space in RAM for all the programs and data you are currently working on. Computers allocate a portion of secondary storage (HDD, SSD etc.) as virtual memory.

Secondary storage. Most common are CDs, DVDs, Blu-ray discs.

Read-only and were primarily used to distribute data such as movies, music and software. However, high-speed internet connections have caused a steep decline.

Recordable. They can be written to one and then only read from that point on. Typically used to archive data.

Rewritable. These discs can be written and read many times. Usually used to back-up files for later retrieval or rewriting.

Magnetic disk drives are often referred to as HDDs (Hard Disk Drives) or just Hard Drives.

Hard Disk Drive, magnetic storage with spinning platters that magnetise.

Type of solid state. Some microcontrollers use a memory chip to store instructions, called flash memory. Flash memory is non-volatile and can be written to and read from.

Secondary storage that uses flash memory to save data electronically. No moving parts.

Optical, Magnetic and Solid State.

Any storage mechanism can fail, and data can be corrupted. Disk reliability is usually measured in terms of the mean time to failure (MTTF).

Base 2 number system. Two states, 0 = off, 1 = on

Binary Digit, a single 1 or 0

4 bits (0000)

8 bits (000000000)