Fig: functions of the operating systems (1)
Hardware consists of physical equipment of the computer. We distinguish equipment within the Case such as: Power supply: it is the equipment that receives electricity from a DC current and converts it to a alternative current AC for the needs of the computer. The power supply may depends on the motherboard of the computer because the wattage varies depends on other equipment inside the computer.
Fig 3: power supply (4)
The motherboard: it is the main equipment of the computer. On it are stored and connected every other equipment. The motherboard is the central piece of the computer. We have many others components installed on the motherboards such as microprocessor, RAM, controller…
Fig 4: the motherboard (5)
Microprocessor: it is the brain of the computer.it means that all the operation on the computer are made by the microprocessor. It is also known as CPU (central processing Unit).it can be measured in megahertz (MHz) or in Gigahertz depending of computer. the performance of the microprocessor is so important that it is essential to any customer to be aware of the number of calculations it can perform before buying a computer . for example, Dell Optiplex 990 works with Intel Core i3 2100 (3.1GHz).
Fig 5: microprocessor (6)
RAM: it is Random access memory. its role is to store instructions or data for a possible processing and its storage is temporally.it holds a list of instructions of an information that is currently working.it can be accessed randomly, it means that it does not have to look in the storage device (hard disk) from the start to find a piece of interest . When we switch off the computer any storage within the RAM, will be erased that is why we say the storage is temporally. RAM is the main memory because we can quickly access any files in the hard disk.
Fig 6: RAM (7)
ROM: it stands for read only memory. ROM differs from RAM in two ways: first it is not changed or erased after the computer is assembled, you can read it but cannot write on it, and second it remains unchanged even after the computer is turned off. 
Fig:19 ROM 
Hard disk: it is the component where data, files, operating systems are saved.it stored large amount of data depending on its size. the records stored are not volatile as in the RAM, but it remains until it is changed or deleted.it is measured in bytes.today we noticed that computer are almost hard disk capacity of 40 gigabytes.this performance of the disk capacity is one of the main measure when we are buying a computer.
Fig 7: the hard disk (8)
Drive controllers: its role is to control data transfer to and from the hard disk.it is a circuits that allows the CPU to communicate with the hard disk and the other kind of disk drive. for example the controller talks to the keyboard and to the mouse to enable the CPU to read information from them(2).we have drive controller such as IDE(integrated drive electronic) and SCSI (small computer systems interface)
Fig 8:drive controllers (9)
CD-ROM Drive: we use this drive to play and read CD-ROM (DISK COMPACT Read only memory) in the computer. we can also play audio CD. a typical capacity of the CD ROM is about 650 megabytes.they are now being overtaken by DVD (Digital Versatile Disk) because of their large capacity storage up to 3.9 gigabytes.
Fig 9: CD ROM drive(10)
Floppy drive: we use this drive to save or read data in a floppy disk. a floppy disk is a small and removable storage devices that record data in square plastic jacket. fig 10: floppy disk drive (11)
The computer software are programs that controls the computer hardware. They command the hardware and tell them what to do and how to do it. We have many kinds of software: operating systems...