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Covers the A-Level content of OCR Chapter 1.1 (components of a computer and their uses)
Components of the Processor and Their Functions
Arithmetic Logic Unit - all arithmetic and logical functions
Control Unit - directs and co-ordinates all functions on the computer by sending out signals
Registers - small memory cells operating at high speeds to temporarily store data
Buses - parallel wires connecting two or more components
describe the:
data bus
address bus
control bus
bi-directional, data and instructions
transmits memory addresses specifying where data needs to be sent to or from
bi directional, transmits control signals to co-ordinate the other buses
what are the 5 types of registers and they’re functions
PC - holds the address of the next instruction to be executed
ACC - stores calculation results
MAR - holds the address of a location to be read from or written to
MDR - temporarily stores the data in the MAR
CIR - holds the current instruction being executed
what are the factors affect CPU performance
amount of cache (quick access memory stored on or near the ram) - reduces the distance the data has to travel, making it faster to access, typically recently or commonly used instructions
number of cores - enables multiple FDE cycles to be carried out at once, making a machine faster
clock speed - faster clock means more instructions can be carried out per second as it synchronises activity on the CPU, can be sped up via overclocking temporarily but can eventually slow down the CPU
what is pipelining
the FDE takes place simultaneously, meaning that there is no ‘gaping’ in the process, stopping the CPU from being idle and wasting time
instruction and arithmetic
what happens in the FDE cycle
fetch - address from PC copied to mar, data copied to mdr, pc goes up by 1, mdr copied to cir
decode - cir split into operand and opcode
execute - the decoded instruction is executed
von Neumann vs harvard architecture
von neumann
shared memory and data buses for both data and instructions causing bottleneck
used in most devices
simpler CU design
harvard
separate buses for data and instructions, which are stored in different memories
used embedded systems
more expensive and complicated CU design
CISC vs RISC
RISC (reduced instruction set computers)
simpler code that uses more lines and more RAM
more taxing for compiler t o translate
each instruction takes 1 cycle, so it can use pipelining
CISC (complex instruction set computers)
more complex code that takes up fewer lines
uses assembly code built into the hardware
less common now, used in embedded systems
multi-core and parallel systems
multicore cpu’s have multiple processors that can complete instructions
parallel systems can do the same thing with one processor, but multi core is much more efficient
the GPU
a co-processor with thousands of cores working in parallel, used previously only for graphics, but now used for repetitive activities like machine learning and linear algebra
input devices
Peripheral devices that allow the user to communicate with a computer e.g. remote, game controller, mouse, keyboard
output devices
peripheral devices that make computer output readable/accessible for the user e.g. screens, vibrations etc
RAM and ROM
Random Access Memory is used to store data and programs in the computer or device. it is volatile
Read-Only Memory stores things like the bootstrap that is permanently required, so its non-volatile
Optical Storage
read and written from pits and lands representing 1 and 0, drawn in by a laser
the most portable and cheap, but very fragile and have low storage potential
examples include dvds, cds and blu-ray
magnetic storage
disks and platters with a read/write head, each portion of the disks gets magnetised to 1 or 0
fragile with moving parts, but not too expensive, low cost per gb
used in HDDs and magnetic tape (cloud storage is typically stored onto magnetic storage)
flash storage
fast and compact, but most expensive per gigabyte
the most widely used
no moving parts, very durable
cloud storage
cheap, can be accessed anywhere with a wifi connection
information on the cloud is an abstraction of hundreds of SSDs and various other drives
Note 
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