Pg.16 - 24

*b/t = between

1) Binary Numbers (BN)
 - Computers file info using Binary.
 - A single binary digit is called a bit.
 - base value for BN is two

2) Hard Drive (magnetic)
 - magnetized area = 1
 - demagnetized area = 2

3) Hard Drive (electric)
 - less likely to fail if they switch b/t only 2 states.

4) Signals
 - Digital signals are concrete, while analog signals vary  (look at pg. 8 in the book for illustrations)
 - Signal gets weaker as it moves down a wire.  Analog signals become distorted easily (because the scale can be from 5 to -5), and do not contain the original info; while the digital signals are of two extremes (1 & 0), so the original info doesn’t change much.

5) Signals (representation)
 - For a light bulb, we can use one digit. 1 meaning it is on, and 0 meaning it’s off.
 - When using two bits, there are exactly four ways we can arrange the bits: 00, 01, 10, 11.
 - 3 bits è 8 combos
 - 4 bits è 16 combos
 - 5 bits è 32 combos
 - 8 bits è 256 combos
 - In general, N bits can represent 2n  unique items.

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1.1 Hardware components

Computer Architecture
- Computer architecture  is the term used to describe how the hardware components of a computer are put together.
 - Info travels b/t components across a group of wires called a bus.

2) The CPU (central processing unit) and the main memory make up the core of the computer.
 - Main memory stores programs and data that are being used.
 - CPU executes program instructions one at a time.


3) Peripherals
 - Almost all devices in a computer sys. Other than the CPU and Main memory are called peripherals.
 - Peripherals operate at the periphery, or outer edges, of the system.
 - Without the Peripheral devices the CPU and main memory would be useless.
 - They include: the monitor, keyboard, etc.

4) Controllers
 - devices that send info back and forth from CPU and main memory to the peripherals.

5) Types of peripherals
 - Input/output (I/O)
 - data transfer devices (i.e. modem, which lets info be sent across a telephone line.

I/O Devices

- most common input devices are the keyboard and mouse. 
 - Others include: bar code readers, joysticks, microphones, virtual reality devices, scanners.

 - most common output devices are the monitors and printers.
- Others include:  plotters, speakers, goggles.

 - Touch screen can handle both input and output.
 - Pixels = “picture elements” (picture created by breaking it up into small pieces)

Main memory & Secondary memory

 - each memory location has a unique number called an address.
 - storage capacity is the total number of bytes(8 bits) it can hold.
 - B/c computer memory is based on the binary sys., all units of storage are power of two.
 - kilobyte (KB) is 1024, or 210

 - Main memory is volatile (lost easily if not supplied by power), Secondary memory is nonvolatile.
 - floppy disk can store 1.44 MB of info.

 - Magnetic tapes = secondary storage (inconvenient, works like a video tape, have to rewind to right place for info). It is a direct access device.

 - RAM (random access memory) & ROM (read only memory), both are a type of direct(or random) access. - RAM: data can be both written and read from it.
 - ROM: data can only be read from it.
 - CD-ROM stores about 650 MB.
 - CD speeds = 153,600 bytes of data per sec.
 - CD - RW has 24x/10x/40x max speeds, 24x = speed for writing CD - R, 10x = speed for writing CD - RW, and 40x = speed for reading.