3.1.1.2 BIOS, CPU, RAM & ROM (B01) Flashcards
BIOS, CPU, RAM and ROM
the start-up problem
For a computer to run, a CPU needs to be given instructions (program code) to execute.
A CPU can only receive instructions from RAM.
When a computer is switched off, everything stored in RAM is lost permanently.
The programs that your computer needs to run (e.g. the operating system) are stored permanently on the HDD.
A CPU is able to transfer program code from the HDD to RAM, but only if it has instructions in RAM telling it what to do.
But, when the computer is first switched on, there are no instructions in RAM, so how does the process get going?
where are start-up instructions stored
ROM
volatile
needs power to preserve the data inside it
BIOS
is the set of instructions (also known as firmware) stored on a ROM chip that is used to start up the computer
comes pre-installed on a personal computer’s system motherboard, and it is the first software to run when powered on
The instructions are copied from the ROM into RAM when ….
the computer is switched on
what does BIOS do
… starts up the monitor, keyboard and other devices.
… checks all the components (e.g. hard disk drive) are working correctly.
… instructs the computer to load the operating system into RAM.
… hands over control to the operating system.
where is BIOS stored
ROM chip
firmware
another name for the BIOS software
boot sequence
The boot sequence begins
CPU starts up and fetches the BIOS from ROM
Instructions from BIOS are loaded into RAM
BIOS starts up the monitor and keyboard
BIOS checks the computer’s components are working
Operating system is fetched from secondary storage
Operating system is loaded into RAM
The BIOS hands control over to the operating system
what is memory
ability to store data using integrated circuits. It is known as primary storage. Data stored in memory is directly accessible to the CPU.
is directly part of the motherboard’s circuitry.
writing and reading
writing- saving data to memory
reading- retrieving data from memory
RAM
random access memory- all data held there is immediately available for access
why is memory/primary storage needed
A CPU needs to read/write data quickly. Reading/writing from secondary storage, e.g. a hard disc, takes a relatively long amount of time, with mechanical restrictions (e.g. how fast the disc can spin, how fast the arm can move), compared to reading/writing to memory (RAM).
primary storage
memory
why isnt all storage memory?
Cost: RAM is more expensive (per unit storage) than secondary storage.
Memory is nearly always volatile, and thus not suitable for long-term storage.
main memory vs secondary storage (give egs)
MAIN MEMORY: fast, expensive, volatile (contents are lost when power is switched off; but ROM is non-volatile), directly accessible to the CPU. Examples: RAM, ROM, memory in the CPU: registers, cache.
SECONDARY STORAGE: slow, cheap, non-volatile, not directly accessible to the CPU. Examples: hard drive, CD-ROM, USB drive.
RAM vs ROM
CPU function
It is where data is calculated / sorted / searched, where decisions are made etc. Anything you do on a computer (typing these notes, playing a game, browsing etc.) involves data being processed by the CPU.
More specifically, a CPU:
Executes program instructions
Processes data
However, its role is larger still: it also controls and coordinates the activities of the whole computer, include the parts involved in the input and output stages.
does all processing take place inside CPU
NO
Processing can take place elsewhere inside a computer, though: e.g. the Graphics Processing Unit (e.g. on a graphics card inside your computer) will do a lot of the processing of data related to graphics. 3D graphics, for example, place heavy demands on a computer and having the GPU deal with it frees up the CPU for other processing activities.
virtual memory
temporarily transferring data from random access memory (RAM) to disk storage
