Chapter 4Discovering Computers

Fundamentals

This is the System Unit (not the CPU)!

The CPU is just one of many components inside of the System

Unit.

Review of Terms/Introduction• Hardware – the physical components of the computer• Software – the instructions telling the hardware to do a

specific task• Definition of Computer (Information Processing

Cycle)– Get Input– PROCESS– Output results– Store information if desired

• This chapter is on the devices/equipment used for processing!

Quick Mention of RAM

• RAM (memory) is used by computers to store information– Any software/program that is running must be in RAM

• Basically, the instructions for those programs must be in RAM

– If you are playing both Solitaire and Minesweep, the main instructions for both of those games must be in RAM

– And don’t forget, the instructions for the operating system are also in RAM, since the operating system is ALWAYS running!!!

Motherboard• The Motherboard (see photo in book) is the main

part of the system unit • Most devices in the system unit reside on,

connect into, snap into, etc…, the motherboard• CPU• Memory• Expansion boards/cards (graphic and sound cards)• Ports• Bus

• For example, a mouse connects into a port, that is part of a card, that snaps into the motherboard.

• This chapter discusses the above in further detail

CPU

• Interprets and carries out instructions• A program/software is made up of a set of

instructions (For example, in solitaire, the instructions could be: deal cards, wait for person to move 1st card, etc…)– In reality, the instructions are much more

detailed then what I listed.– The CPU carries out the instructions one by

one

Parts of CPU: Control unit

• One component of the CPU is the control unit. It’s function is to:– FETCH one instruction from RAM/memory– DECODE (or translate) instruction into

something computer can understand– EXECUTE the commands (or send instruction

to the ALU to execute)– STORE or save the results of that instruction

back into RAM/memory

More on Parts of CPU:ALU

• The ALU is the part of the CPU that actually executes the instructions.– Specifically, it does the arithmetic and logic

calculations

More keywords relating to CPU

• Pipelining– Pipelining is when the CPU fetches one

instruction while the previous instruction is still being decoded

– Great explanation of this in book– Most modern day CPUs all have this feature– Obviously this means more instructions can be

executed, which means your computer becomes faster

Clock Speed of CPU

• Obviously, the faster the CPU the faster your computer– NOTE: CPU is one of many things that affect the speed

of your computer. We will talk about other factors later– Similar to how a clock ticks, the CPU clock also ticks– During the duration of a tick, a certain number of

instructions are executed– The more ticks per second, the more instructions that

can be executed per second– The CPU clock is measured in MegaHertz (MHz)

• One million ticks per second

More on MHz

• 1 MHz– 1 million ticks per second

• 500 MHz– 500 million ticks per second

– Remember, more ticks, mean more instructions can be executed

• Nowadays you can also measure CPUS in GHz (GigaHertz)– 1 billion ticks per second

Who makes CPUs/Processors

• Think of the Nissan Car company– Nissan makes cars, but it makes various models:

Sentra (least powerful), Altima (more powerful), Maxima (even more powerful)

• Same with makers of Processors– Intel, AMD, Motorola, are all

companies/manufacturers of processors– Intel makes various “models”: Celeron (for slower

end PCs), Pentium, Xeon, and then Itanium (most powerful)

More on Processor Manufacturers

• Back to the car analogy … – Even though Nissan Sentras and Nissan Maximas can

both go 80 miles an hour, a Maxima is still more powerful

• Same with processors. – For example, even though an Intel Celeron can be

600MHz and Intel Pentium can be 600MHz, a Pentium is generally still more powerful

• Keep this in mind when buying computers!

Data Representation

• Let’s talk about how a computer stores information/data

• People communicate with words– Analog – using signals to represent data

• Computers communicate with 0’s and 1’s– Digital – using two electrical states (on-1 and

off-0)

More on Data Representation

• Think of Morse code– To communicate with Morse code, you only have two

options (long dashes/sounds and short dashes/sounds)• The letter A could be a short dash followed by a long dash• The letter N could be a long dash followed by a short dash

• There is a similar code for computers using 0’s and 1’s (or really, the absence of an electrical state and the presence of an electrical state)– There is more than one code a computer can use:– ASCII, EBCDIC, UNICODE

ASCII Codes

• The code used on most PCs and minicomputers is called the ASCII code– EBCDIC code is used on mainframe computers

• A bit is a 0 or 1 (an off or on state)• In the ASCII code, each character is represented by 8

bits– The letter A is 01000001– The letter N is 01001110

• Another term for 8 bits is 1 BYTE• When you press the letter A on the keyboard, the signal

is converted from the letter A to 01000001

More on bits and bytes

• A bit is the smallest unit of data• 8 bits is 1 byte (basically, 1

character/letter)• 1 Kilobyte (KB) translates to approx. 1000

bytes• 1 Megabyte (MB) approx. 1 million bytes• 1 Terabyte (TB) approx. 1 trillion bytes• KNOW THIS!!!

Back to Memory

• Think of memory as the computer’s storage area

• There are three main types of memory that we will discuss:– RAM

• Cache (pronounced cash)

– ROM– CMOS

RAM Memory-volatile

• Random Access Memory (volatile)– Everything that is running on your computer (the

instructions) is stored in RAM. – RAM is cleared if the computer is turned off

• When you first turn the computer on, the operating system (Windows 95/98) instructions are loaded into RAM

• If you start Solitaire, then the Solitaire instructions are loaded into RAM (with the operating system)

• Remember, the CPU “fetches” the instructions one by one from RAM

• When you turn off the computer, everything is cleared from RAM. When you boot up your computer the OS has to be copied back into RAM. The solitaire instructions will only be copied back into RAM if you decide to start it up again.

Cache Memory

• Memory Cache or RAM Cache is a part of RAM that stores the most frequently used instructions/data– Cache is much faster– The CPU looks in the cache for data. If it’s there, it

grabs it from the cache, which is much faster. If it’s not there, it gets it from RAM, which is a little slower

• Cache is faster, but more expensive, so you have a limited amount

• Keep this in mind when buying computers! More cache is more desirable!

ROM Memory-nonvolatile

• Read-Only Memory (non-volatile)– We will discuss this in more detail in a later chapter– Contains instructions that are permanent, so to speak– The contents of ROM are NOT lost when the

computer is turned off … it generally contains the same instructions

– These are instructions that are used when the computer is turned on

– More on this in chapter 8, for now, realize that these instructions are permanent, and this is a non-volatile memory.

CMOS Memory - nonvolatile

• Pronounced (see-moss)• Contains information about your computer’s

configuration (type of keyboard, mouse, disks, current date, time, etc…)

• Has a battery which allows the date and time to remain even when computer is off

• Contents of CMOS do not get wiped out when the computer is turned off, though it does get updated when you make changes to your computer– For example: when you add a new disk, etc…

Memory Slang

• Most people ask – How much memory do you have?– How fast is your memory?

• Generally they are referring to RAM.

• Just make sure you understand that there are other types of memory (RAM cache, ROM, CMOS, etc…)

Memory Performance

• Performance can be affected by your CPU speed– The faster the CPU, the more instructions it can process,

the faster your computer

• Access time of memory also affects speed– The faster the CPU can access info from memory, the

faster the CPU can start processing

• SRAM is one type of RAM• DRAM is another type of RAM

– SRAM has faster access times than DRAM, but is more expensive

• Keep this in mind when you buy computers

Memory Capacity

• Your computer has a limited amount of memory

• Memory capacity is measured in MBs. – How many MBs of RAM (memory) do you have?

– 32MB is the minimum nowadays, but 64MB or 128MB is better

• Your computer has a certain number of slots available only for memory cards. If you need more memory, you can add a new card.

• Some memory cards are 32MB, some are 64Mb, etc… Buy the card size you need, or can afford.

• Just make sure you have a free memory slot.

If you plan to buy memory…

• 1. Make sure the memory card you buy is compatible with the memory currently in your system– Check the website for the PC manufacturer (Dell, IBM,

etc…)– Look up your PC model– It should say which memory cards are compatible

• 2. If you have more than one size (64MB card of memory and 32MB card of memory), put the larger card in the first slot. Just a little tip. It’ll work either way, but this is the recommended way to get more out of your memory.

How Memory Capacity Affects Performance

• The more memory, the more instructions your computer can hold at one time, the faster your computer

• If the instructions or data cannot fit in memory, it sometimes has to go look for it somewhere else (like the CD or disk drive … which is much much slower)

• Sometimes if you run out of memory your computer can hang

Expansion Cards and Expansion Slots

• Know some of these keywords:– Card or Expansion Card

• Video card

• Sound card

• NIC card

• Modem card

– Plug and Play

Ports• Plug in devices to a port

– Think of it as a wall socket on the computer– Plug in a keyboard to a port– Plug in a printer to a port

• Serial ports transmit data one bit at a time– Slow, so used for keyboards, mouse, and modems

• Parallel ports transmit more than one bit at a time– Faster, used for printers

• Other ports are listed in book (MIDI, USB, SCSI, IrDA)• Ports are different shapes and sizes. Look at chart in book. Serial

ports can have many shapes. Parallel ports can have many shapes. Make sure your cable matches the shape of the port!

• READ ABOUT USB ports!!!

BUS

• How does one device on the computer communicate with another– A keyboard plugs into a port, which is attached to the

motherboard

– A disk is attached to the motherboard with a cable

– Memory snaps into the motherboard

– CPU resides on motherboard

• How does information from the keyboard get to the disk, get to memory, get to the CPU?

More on BUSES

• The motherboard has channels called BUSES

• The bits travel on the buses from one device to another

• The faster the bus, the faster the data travels, the faster your computer

Summary• The CPU speed, memory capacity, memory speed,

amount of cache, bus speed, etc… can all affect your system’s performance, though the CPU speed is the primary factor for a home PC.

• All programs that are currently running are stored in RAM. OS has to be loaded into RAM each time you start up the computer.

• The CPU processes each instruction one by one, by fetching them from RAM

• A computer stores data in bits (bytes, megabytes, etc…)• All items in the System Unit are ultimately connected to

the Motherboard• Buses on the motherboard allow the bits to travel from

one device to another

Practice

• How many bits in 1 byte?– 8

• How many bits in 10 bytes?– 8 * 10 = 80

• 40 bits equals how many bytes?– 40 / 8 = 5 bytes

• How many bytes in 1KB?– 1024 (or approx. 1000)\

• How many bytes in 1MB?– Approx. 1 million

• Approx. how many bits in 1 KB?

– 1KB= approx 1000 bytes– 8 * 1000 = 8000 bits

• CPU speed is measured in– Hz (MHz or GHz)

• Memory capacity is measured in:

– Bytes (MB or GB)

• Intel makes what brands of processors? (which is slowest, fastest)

• AMD makes what brands of processors?

The End