Hardware: The physical parts of a computer.
Transistor: A tiny electrically operated switch that can alternate
between "on" and "off".
Chip (Microchip): A tiny piece of silicon that contains millions
of transistors and other electronic components.
Modern-day computer systems usually contain, at a minimim, the following
- The System Unit
- Motherboard (aka System Board)
- CPU (Central Processing Unit)
- Memory, such as RAM, ROM, Cache, and Flash
- Expansion Slots
- Secondary Storage, such as hard disk drives, CD-ROMs, etc.
- Input / Output Devices
- Communications Devices
The System Unit
- The Motherboard is the main circuit board for the computer,
containing both soldered, nonremovable components along with sockets
or slots for components that can be removed. The motherboard holds
the CPU, RAM and ROM chips, etc.
- The Central Processing Unit (CPU) is the "brain" of the
computer. It executes instructions (from software) and tells other
components what to do.
- The Intel Pentium is a popular processor for IBM-PCs.
- The PowerPC is a popular processor for Macintoshes.
- There are 2 parts of the CPU: The ALU and Control Unit.
- The Arithmetic Logic Unit (ALU) performs
arithmetic operations (such as addition and subtraction)
and logical operations (such as comparing two values).
- The Control Unit deciphers and carries out
- Different CPUs have different types of instructions, so software
made for one type of CPU will not run on other kinds.
- The word size denotes how many bits of data a CPU can
process at once. 32 bits is the standard word size for CPU's
used in personal computers today. The higher the word size,
the faster a CPU can execute instructions.
- The System Clock is an "electrical pulse generator" that sends out
a pulse of electricity at regular intervals. The electronic components
of the computer need these electric pulses in order to perform work. The
more pulses sent out by the system clock, the faster the computer. The
first personal computers had clock speeds of 8 MHz (8 million pulses per
second); today's PC's have clock speeds greater than 3.2 GHz (3.2 billion
pulses per second).
- Bus Lines are "electrical data roadways" (i.e. wires) through which
bits of information are transmitted between the CPU and other components.
The bus size denotes how many bits can be transmitted at once. In
general, this should be the same as the CPU word size.
- Memory Chips
- Random Access Memory (RAM), also known as Main Memory
or Primary Storage, is used to hold instructions and data
while they are being used. RAM is volatile, meaning its
contents are lost when the power goes off. RAM is more than 1000x
faster than the fastest secondary storage (see below).
- Read Only Memory (ROM) chips are non-volatile memory
that generally contains instructions for "booting" the computer
(i.e. loading the operating system when the computer starts up).
- CMOS chips are powered by a battery and contain so-called
"flexible information" such as the type of hard drive your computer
is using and the current date and time.
- Flash chips do not require electricity or a battery yet are
non-volatile. They are used in computers, cell phones, digital
- Cache memory is special high-speed memory that temporarily
stores instructions and data the CPU is likely to use frequently.
This speeds up processing. Level 2 or external caches generally
range in size from 64 Kilobytes to 2 Megabytes.
- Expansion Slots are sockets on the motherboard that you can plug
expansion cards into. To plug a card into a slot, you must open
the system unit. A card contain a socket on its end that sticks out from
the system unit so a cable can be plugged into it. Common types of cards
are graphics, sound, and network cards.
- Ports are sockets that are on the outside othe system unit, meaning
you can easily plug a cable into a port without opening the system unit.
- Serial ports transmit one bit of data at a time.
- Parallel ports transmit 8 bits of data at a time.
- Universal Serial Bus (USB) ports are much faster
than serial or parallel ports and allow multiple devices to be
connected to the same port.
- Devices that "permanently" hold data and information (i.e. programs).
- Non-volatile memory; when the power goes off, contents are still saved
(unless there is an error).
- Used to store instructions and data while they are not
- A floppy disk is a removable (i.e. portable) platter made of
mylar plastic that is magnetized. Bits of information are stored in
concentric rings called tracks on either side of the platter.
The current floppy disk standard is a 3 1/2" platter in a hard plastic
case that holds 1.44 Megabytes of information. A Zip disk, on
the other hand, can hold up to 250 Megabytes.
- A hard disk is similar to a floppy disk but uses metal platters to
store information. Hard disks are not only much faster than floppy disks
but can hold huge amounts of data (hundreds of gigabytes).
- Both floppy and hard drives use a read/write head, which is basically
a magnet, to read/write information from/to tracks on a platter. In a hard
drive, the read/write head and platter(s) are enclosed together in an air-tight
package, making hard drives less susceptible to damage. The read/write head
hovers above the platter but should not touch it. If touched, the platter
can be damaged, resulting in the loss of some or all the data on the platter.
This is known as a head crash.
- Magnetic tape is used mostly for backups. These are very slow because
you have to fast forward or rewind to the right spot. However, they are very
- Optical discs use optical technology (i.e. lasers) instead of magnetic
technology to store information.
- CD-ROM stands for Compact Disc - Read Only Memory.
- CD-R stands for Compact Disc - Recordable and can be written to only once.
(Also known as CD-WORM: Compact Disc - Write Once, Read Many.)
- CD-RW stands for Compact Disc - Re-writeable (or Read/Write).
- DVD-ROM stands for Digital Versatile Disc - Read Only Memory.
- DVD-R stands for Digital Versatile Disc - Recordable and can be written to only once.
(Also known as DVD-WORM: Digital Versatile Disc - Write Once, Read Many.)
- DVD-RW stands for Digital Versatile Disc - Re-writeable (or Read/Write).
- CD's can hold approximately 650 Megabytes of data while DVD's can hold up to 17 Gigabytes.
Input / Output Devices
- Input devices translate data into a form the computer can understand.
- The keyboard is the most common input device, but this type of data entry is very slow
- Direct input devices are much faster and less error-prone.
- Pointing devices such as the mouse, trackball, and touchpad
allow you to manipulate a cursor on the screen.
- Scanning devices read data directly. For example, OMR (Optical Mark
Recognition) devices (such as a scantron machine) can sense marks on paper. Even
more advanced are OCR (Optical Characgter Recognition) devices, which
attempt to read letters. Bar Code Readers are often used in grocery stores to
- Output devices translate information into a form humans can understand.
- The Monitor (or Display Screen) is the most common type of output device. It
produces softcopy (i.e. temporary) output on a screen.
- The Printer is the most second most common type of output device. It
produces hardcopy (i.e. "permanent") output on paper.
- A Laser Printer uses a photoelectric drum and powdered ink, similar to a
copying machine, to produce output.
- An Inkjet Printer produces output by spraying droplets of liquid ink onto
the paper from small nozzles. It is the most common type of printer in use today
and is generally very inexpensive.
- These allow your computer to send/receive data to/from other computers.
- A modem sends information over a phone line. Modems are slow and susceptible
to problems such as phone line static.
- A network card sends information over a network cable. These can be used to hook
up a computer to a local area network (LAN) or to an Internet Service Provider via a
cable modem or DSL (for Internet access).
Measurements in Computer Science
- Bit (Binary Digit): Can only have a value of either 0 or 1.
- Byte: 8 bits (also known as a Character).
- ASCII: A code that assigns characters, such as 'a', 'b', etc. unique 8-bit values.
This allows information created on one computer to be understood by other
- There are other codes besides ASCII, but ASCII is the most common, used in virtually all
personal computers and most larger computers as well.
- Kilobyte: 1024 bytes (or 2^10 bytes).
- Megabyte: 1024 * 1024 bytes (or 2^20 bytes). Roughly one million bytes.
- Gigabyte: 1024 * 1024 * 1024 bytes (or 2^30 bytes). Roughly one billion bytes.
- Terabyte: 1024 * 1024 * 1024 * 1024 bytes (or 2^40 bytes). Roughly one trillion bytes.