Components of Computer

Memory Unit Most important part of the computer Used to store data and instructions that are currently in use Main memory consists of memory cells Each cell is assigned a unique number known as memory address Data is stored into the memory cells in binary form Storage in main memory is temporary Contents are erased when computer is turned off Known as volatile memory

Memory Unit Control unit performs the following for main memory ◦ Stores the data and instructions into the main memory ◦ Supplies the data and instructions from main memory to other parts of the computer ◦ Stores the processed results back into the main memory

Memory Unit The basic storage unit of memory is bit which stands for Binary Digit A bit is a binary digit 0 or 1 Main memory consists of large number of electronic switches Each switch can have either of the two states i.e. ON and OFF Data and programs are stored in the form of switch states Storage capacity of main memory is measured in bytes

Memory Unit A byte is a group of 8 bits One character take one byte of memory Amount of data and program size are also measured in bytes ◦ 1 Byte=8-bits ◦ 1 Kilo Bytes=1024 Bytes ◦ 1 Mega Bytes=1024 Kilo Bytes ◦ 1 Giga Bytes=1024 Mega Bytes ◦ 1 Tara Bytes=1024 Giga Bytes

Memory Unit

Memory Unit

Memory Unit

Types of Memory Unit Memory unit is classified into two basic types: ◦ RAM ◦ ROM

Random Access Memory (RAM) Consists of memory chips that can be read from and written to by the processor When the computer is powered on, certain operating system files load into RAM from the storage device such as hard disk Operating System remains in RAM as long as the computer has continuous power The program and data must be transferred to RAM before to run the program to process the data Storage capacity of RAM is measured in KB or MB

Random Access Memory (RAM) The large RAM size increases the accessing speed of the computer More RAM means the computer can use powerful program with large size Improves the data processing speed of the computer

Random Access Memory (RAM)

Three Types of Memory Module SIMM DIMM RIMM

to-my-computer/ mx/MLM mem- rdram-rimm-256mb-ppresario- 7111la-compaq-dell-sony-aqui- _JM

Types of RAM DRAM SRAM MRAM

Dynamic Random Access Memory Most common type of RAM used to store data and instructions Requires an electric current to maintain its electrical state In order to maintain the data, the chip is refreshed frequently, otherwise data may be lost During refreshing process, the CPU has to wait to read and write data in DRAM Decrease the processing speed of the computer The most important DRAM chips are: ◦ SDRAM : Synchronized with clock ◦ RDRAM : Use Pipelining Technique

Static Random Access Memory It can store data without any need of frequent recharging CPU does not need to wait to access data from SRAM during processing Faster than DRAM Utilizes less power More Expensive

Magneto resistive Random Access Memory Stores data using magnetic charges instead of electrical charges Uses less power than other RAM technologies Ideal for portable devices Greater storage capacity Faster access time Retain its content when the power is removed from computer

Difference between SRAM and DRAM SRAMDRAM Faster than DRAMSlower than SRAM More ExpensiveLess Expensive Does not need to be power- refreshed Has to be refreshed after each read operation Utilizes less powerUtilizes more power Holds data indefinitely as long as the computer is turned on Holds data dynamically not indefinitely More complex and less compact Less complex and more compact

Read Only Memory Contains the instructions that are permanently stored by the manufacturer when the manufacture the chips Recording data or instruction permanently into this kind of memory is called “burning in the data” Instruction stored in ROM is read only Not reprogrammed by the user Programs stored in ROM are called firmware Non volatile memory

Read Only Memory ROM contains the Basic Input / Output System (BIOS) which is a set of instructions that are automatically activated when the computer is turned on Computer uses the instruction of ROM at the time of booting for the following purpose ◦ To check different units of computer system ◦ To load the operating system into the computer memory

Types of Read Only Memory ROM is further divided into ◦ PROM (Programmable Read Only Memory) ◦ EPROM (Erasable Programmable Read Only Memory) ◦ EEPROM (Electrically Erasable Programmable Read Only Memory)

Difference between PROM and EPROM PROMEPROM The user can write instructions on PROM only once The user can write instructions on EPROM many times The instruction written by the user cannot be erased from PROM The instruction written by the user can be erased from EPROM If there is an error while writing on PROM, it becomes unusable If there is an error while writing on EPROM, it can still be used again It provides less usability as instructions are written only once It provides more usability as instructions are written many times

Difference between RAM and ROM RAMROM Temporary MemoryPermanent Memory Enables data to be both read and written to memory and data can be changed or deleted Instructions written in ROM can be only read but cannot be changed or deleted Instructions in RAM change continuously as new programs are executed and new data is processed It is not possible to write new information or new instructions into the ROM, so ROM is non volatile memory When the power is turned off, all the data and programs are erased from RAM. So RAM is a volatile memory When the power is turned off, the instructions stored in ROM are not lost, therefore ROM is non-volatile memory Instructions are written into the RAM at the time of execution Instructions are written into ROM at manufacturing time

Cache Memory Small and very fast memory Designed to speed up the transfer of data and instructions Located inside or close to CPU chip Faster than RAM Store most frequently used data and instructions

Levels of Cache Memory The level number refers to distance from CPU Different levels of cache memory are as follows: Level 1 (L1) Cache Level 2 (L2) Cache Level 3 (L3) Cache

References Introduction to Information Technology by Riaz Shahid, CM Aslam and Safia Iftikhar