1.2 Memory and Storage Flashcards
OCR GCSE Computer Science J277
Main Memory
where data and instructions are stored so they can be accessed directly by the CPU
Secondary Storage
used to permanently store data such as the operating system and user’s files
RAM (Random Access Memory)
holds all of the data and instructions that are currently being processed.
Memory Addresses
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.
Volatile
Power is required to hold the data.
Read Only Memory (ROM)
typically used to store the boot sequence (BIOS) for a computer.
Non-volatile
will not lose its data when the power is switched off.
Basic Input/Output System (BIOS)
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.
Pages
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.
Virtual memory
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.
Optical
Secondary storage. Most common are CDs, DVDs, Blu-ray discs.
ROM Disc
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.
R discs
Recordable. They can be written to one and then only read from that point on. Typically used to archive data.
RW discs
Rewritable. These discs can be written and read many times. Usually used to back-up files for later retrieval or rewriting.
Magnetic
Magnetic disk drives are often referred to as HDDs (Hard Disk Drives) or just Hard Drives.
HDD
Hard Disk Drive, magnetic storage with spinning platters that magnetise.
Flash memory
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.
Solid State
Secondary storage that uses flash memory to save data electronically. No moving parts.
Types of Secondary storage
Optical, Magnetic and Solid State.
mean time to failure (MTTF)
Any storage mechanism can fail, and data can be corrupted. Disk reliability is usually measured in terms of the mean time to failure (MTTF).
binary
Base 2 number system. Two states, 0 = off, 1 = on
Bit
Binary Digit, a single 1 or 0
Nibble
4 bits (0000)
Byte
8 bits (000000000)
Kilobyte
1024 (or 1000) bytes
Megabyte
1024 (or 1000) kilobytes
Gigabyte
1024 (or 1000) megabytes
Terabyte
1024 (or 1000) gigabytes