Componentsof a Computer System

• The physical parts and components of the computer, which includes it’s main parts and peripherals (tangible – can be manipulated in physical terms)

• Examples of Hardware are the monitor, keyboard, mouse, the motherboard

• The hardware is used to input data into the computer system which processes the data into information

Intro | Hardware

The System• In the simplest way, the computer

works through the Input-Process- Output system– The user creates commands to the

computer, the Input– The computer processes the command,

the Process– The computer responds (“obeys”) after

the processing, the Output

The System• The computer system works like the human

body: the Central Processing Unit controls the other parts of the computer and carries out the instructions and does the processes for the output

• These processes are not recognizable by human facets because the processes are converted into electrical signals of digital code

• These processes are relayed to the various units through the buses: the address bus, the control bus, and the data bus

The Memory• The part of the system where the data and

software is stored temporarily– Can either be primary /main storage , the

area in the computer is stored for quick access by the computer’s processor (RAM/Random Access Memory)

– or secondary storage, where programs and data are kept on a long term basis, slower to access yet offers more storage space (Hard Disk)

• The Memory is connected to the processor by a line called a bus

Memory Hierarchies• Purpose is to provide a memory system

with the cheapest and the fastest type of memory

• Locality of reference – a phenomenon describing same value or related storage locations being frequently accessed

• Resulting in code and data most likely to be used are stored in quicker memories, while less frequently used ones are stored on slower ones

Memory Hierarchies• A memory hierarchy works as

follows– A memory location is accessed

and the contents of the memory are placed into the highest level, expected to be accessed in a short period of time

– As new locations are accessed, new pieces of code and data are brought into the higher levels of the hierarchy replacing older ones, which goes to the lower levels

– The Lower the hierarchy goes, the access time gets larger, the capacity increases and the number of bits per cost

Memory Capacity• The computer memory is composed

of the registers within the processor: the main storage unit (the Primary) and the auxiliary storage devices (the Secondary)

Memory Performance Access Time• Performance and speed are indicated by Access

time and Cycle time• Access time is the time elapsed from the time

the processor sends the read/write instruction until the data delivery/acceptance is completed

• For the processor to access the main storage unit data, 3 stages are necessary– Time during which the processor requests the data be

read out– Time during which the processor selects the main

storage unit address with the address bus– Time during which the data of the said address is

transfered through the data bus

Memory Performance Cycle Time• Among the storage elements of the

storage unit, there are some where memory fades over time

• Thus the refreshing operation that rewrites data at regular intervals becomes necessary

• Cycle time is the lapse of time that include the point up to the preparation.

Memory Address• The Bit is the most basic unit of memory– Either one of two values: 1 or 0– 8 bits make a byte (ex. 11001011)• 1024 bits make a kilobyte (Kb)• 1024 Kb makes a megabyte (Mb)• 1024 Mb makes a gigabyte (Gb)• 1024 Gb makes a terabyte (Tb), etc.

• Bits are stored within spaces called memory cells (also known as “words”) with a typical size of a byte (8 bits)

Auxiliary Storage Devices• Auxiliary storage devices are the aforementioned

secondary storage, that is not directly accessible by the CPU, because it is not accessed via the input/output channels, being an external device

• Examples include flash drives, flash disks, CDs, DVDs, floppy disks, magnetic disks, punched cards (obsolete) magnetic tapes and memory cards.

• Auxiliary storage has similar attributes to other I/O units, thus most of the ideas apply also to the Auxiliary devices

Auxiliary Storage Devices• Auxiliary storage units behave in a manner similar

to I/O, though users do not interact directly with the device (facilitated by the computer itself)

• Auxiliary storage devices has data transmission rates that may be significantly higher than other kinds of I/O devices but still below the internal speed of the processor

• An auxilliary storage device uses two main purposes– Serving as an extension of the main memory (ex. Local

Disks :D and :C, with external drives such as :G and :F)– A medium to permanently archive information/data/files

such as music, graphics, documents, software