The case houses most of the critical components (parts) of the computer. The most important is the central processing unit (CPU) or chip. The CPU is mounted on the motherboard. The printed circuits on the motherboard allow the CPU to communicate with the other components (parts) of the system. Also in the case are the drive units (hard disk (HD), floppy disk, and CD-ROM) in our machines. These can be both input (read) and output (write) devices.
The keyboard is the primary input device. The keyboard allows the user to communicate with the CPU using letters, numbers, and special key combinations.
The monitor (screen) in the primary output device. This allows us to visually see the results of our inputs. Some monitors have built-in speakers (audio output) and a microphone (audio input) or webcam (video input).
The mouse is an (input) pointing device. Moving the mouse on its pad causes an arrow (cursor) to move on the screen. Pressing (clicking) the left or right button will cause the CPU or program to perform functions based on the location of the cursor.
The mouse and keyboard attach to the motherboard using standarized PS2 or USB connectors. Mice and keyboards are usually interchangeable.
Many additional devices can be added to the system.
Measuring Space or Capacity
A bit is the computer’s smallest measure of capacity. Eight bits in a row equal a byte. Bytes are the basic measurement for capacity. Since bytes are so small we use shorthand when referring to large numbers.
A kilobyte (KB) is one thousand (1000) bytes. A saved document or picture may be measured in kilobytes.
A megabyte (MB) is one mllion (1,000,000) bytes. Most current programs require megabytes of disk space and RAM (Random Access Memory).
A gigabyte (GB) is one billion (1,000,000,000) bytes. Hard disks can now store dozens, even hundreds, of gigabytes.
Some hard disks and drives can store terabytes or one trillion bytes. In the future, we may see exabytes or one quadrillion bytes.
We store data on different media. Floppy disks can hold 1.44 MB of data or programs. Most programs now exceed the capacity of floppies. Floppies are read/write and removable so data can be saved and moved.CD-ROMs can hold up to 700 MB and DVD-ROMs can hold up to 4.7 GB. most programs are sold now on either CD-ROMs or DVD-ROMs. ROM means Read Only Memory; the computer can read and install programs or data from them but cannot write (output) to them. CD-Rs, DVD-Rs, and DVD+Rs, can be written to once, and then they act like CD-ROMs and DVD-ROMs. CD-RWs and DVD-RWs can be used like floppies with much greater capacity. Hard disks are growing rapidly in capacity. You can both read and write to hard disks.