Binary and Hard Disk Aslin Izmitli PEOPLE Program

Outline How do computers store numbers Hard drive and its components Binary numbers

How do Computers Store Numbers Computers are constructed of digital electronics => two states: “on” “off” Binary number system consists of 0 and 1 only On-off patterns are used to encode numbers using binary number system Most computer electronics Voltage levels CD-ROM Microscopic dark spots on disk surface Hard disk Magnetism Computer memory Electric charges on capacitors

Cassette Tape vs. Hard Disk They use the same magnetic recording techniques Easily erased-written Easily erased-written “remember” for many years “remember” for many years Cassette Tape Hard Disk Recording material On plastic strip On high-precision aluminum or glass disk To get to a point Fast forward (several minutes) You can move instantly Read-write head Touches the tape “flies” over the disk Move – Spin 2 inch/second 3000 inch/second (170mph) Info storage Magnetic domains Extremely smaller magnetic domains

Hard Drive Hard disks are used in all desktop computers, servers, super computers etc. They are also VCR type devices or video recorders that use hard drives instead of tape They store changing digital information in a relatively permanent form. They give computers the ability to remember things when the power goes out. Now see what we can find in a hard drive (opening a hard disk ruins it!!) (opening a hard disk ruins it!!)

Electronic Board A hard drive is a sealed aluminum box with controller electronics attached to one side. The electronics are all contained on a small board that detaches from the rest of the drive The electronics control the read/write mechanism and the motor that spins the platters. control the read/write mechanism and the motor that spins the platters. Magnetic domains -> bytes (reading) Magnetic domains -> bytes (reading) Bytes -> Magnetic domains (writing) Bytes -> Magnetic domains (writing)

Beneath the Board the connections for the motor that spins the platters a highly-filtered vent hole that lets internal and external air pressures equalize

Removing the cover from the drive The platters typically spin at 3,600 or 7,200 rpm when the drive is operating are manufactured to amazing tolerances and are mirror-smooth The arm holds the read/write heads and is controlled by the mechanism in the upper- left corner is able to move the heads from the hub to the edge of the drive extremely light and fast, can move from hub to edge and back up to 50 times per second

Mechanism moving the arms Incredibly fast and precise. Can be constructed using high-speed linear motor Many derives use a ‘voice coil’ approach – the same technique used to move the cone of a speaker von your stereo

Platters and Heads Multiple platters to increase information storage capacity This drive has three platters and six read/write heads

Storing the Data Data is stored on platter surface Tracks -> concentric cycles Tracks -> concentric cycles Sectors -> pie-shaped wedges on a track Sectors -> pie-shaped wedges on a track A sector contains a fixed number of bytes (256, 512 etc.) Sectors are often grouped together into clusters Low level formatting The drive establishes tracks and sectors on the platter Prepares the drive to store blocks of bytes High level formatting Writes the file-storage structures, like file allocation table into sectors Prepares the drive to hold files

How Does Binary Work? Decimal number system 10 digits (0 to 9) 10 digits (0 to 9) Add a second column worth 10 times the value of the first column Add a second column worth 10 times the value of the first column Expanded notation: 3 x x = x x = x x x = x x x = 1032…

Binary Number System Only contains two digits: 0,1 Add a second column worth 2 times the value of the first column To convert a number from binary to decimal, use expanded notation: = 1x32 + 0x16 + 1x8 + 1x4 + 0x2 + 1x1 1x32 + 0x16 + 1x8 + 1x4 + 0x2 + 1x1 = 45 = …

Binary  Decimal Any desired amount can be represented using 1 and 0. Examples 1 == == == == == ==  a power of 2 0  zero Examples 0001  2^0 =  2^0 =  2^1 =  2^1 =  2^2 =  2^2 =  2^3 =  2^3 = = = = = = = 7

Larger Numbers Numbers from 1 to = = = = = = = = = = = = = = = = 15 Bigger whole numbers  more bits more places in binary number = = 133 This is 8 bits == 1 byte

Larger Numbers = = 133 This is 8 bits == 1 byte Alphanumeric characters are represented with 8 bits A == 65 == Kilobyte = 1024 bytes (1024 = 2^10) Megabyte ~ a million bytes Gigabyte = 1000 megabytes

Typical Sizes Typical RAM is megabyte Typical Hard disks are 40 – 80 gigabyte 1 byte == 1 character  hard disk might hold million characters ~ million words of raw text  hard disk might hold million characters ~ million words of raw text Real numbers, fractions, very large numbers  floating point arithmetic  floating point arithmetic

Binary numbers are great! Simple to work with No big addition and multiplication tables to learn No big addition and multiplication tables to learn Just do same things over and over very fast Just do same things over and over very fast Just use two values of voltage, magnetism or other signal Hardware easier to design and more resistant Hardware easier to design and more resistant

ASCII Table Write your name in ASCII Table Password 5 letter word

Binary Addition Decimal System Sum >= 10  add 1 to the column on the left Sum >= 10  add 1 to the column on the left Binary System Sum >= 2  add 1 to the column on the left Sum >= 2  add 1 to the column on the left Example: = 11 Example: = =

Binary Addition Second Way Convert the numbers to decimal Convert the numbers to decimal Add the decimal numbers Add the decimal numbers Convert the sum to binary Convert the sum to binary