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COMMON COMPUTER HARDWARE

COMMON COMPUTER HARDWARE. Our PCs are data processors The PC's function is simple: to process data, and the processing is done electronically inside the CPU and between the other components. That sounds simple, but what is data, and how is it processed electronically in a PC?.

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COMMON COMPUTER HARDWARE

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  1. COMMON COMPUTER HARDWARE ES103

  2. Our PCs are data processors The PC's function is simple: to process data, and the processing is done electronically inside the CPU and between the other components. That sounds simple, but what is data, and how is it processed electronically in a PC? ANALOG DATA : the type of data we use in our everyday life : photos, sound, letters, numbers …. these can vary in type – unusable for PCs DIGITAL DATA : PC is an electrical unit therefore can only deal with simple electrical data: electric switches : ON / OFF OFF ON ES103

  3. The PC is filled with these switches (computers first had vacuum tubes – computers today have transistors). DATA PROCESSING = understanding these 1’s and 0’s … Each 0 or 1 is called a bit. Bit is an abbreviation of the expression BInary digiT. It is called binary, since it is derived from the binary number system: ES103

  4. How does the computer process this data? ES103

  5. DATA PROCESSING The most basic data processing is word processing. When we do word processing, we work at a keyboard similar to a typewriter. There are 101 keys, where we find the entire alphabet A, B, C, etc. We also find the digits from 0 to 9 and all the other characters we need:,.-;():_?!"#*%&etc.. All these characters must be digitized = They must be expressed in 0s and 1s. Bits are organized in groups of 8. A group of 8 bits is called a byte. Why 8??? 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 = 256 different bytes are possible ! ES103

  6. ASCII means American Standard Code for Information Interchange. (originally 7-bit) ANSI is the 8-bit encoding system developed by the American National Standards Institute. It is an industry standard, which assigns letters, numbers, and other characters within the 256 slots available in the 8 bit code. ES103

  7. The ASCII table is divided in 3 sections: 1) Non printable system codes between 0 and 31. 2) "Lower ASCII" between 32 and 127. This part of the table originates from older, American systems, which worked on 7 bit character tables. Foreign letters, like Ø and Ü were not available then. 3) "Higher ASCII" between 128 and 255. This part is programmable, in that you can exchange characters, based on which language you want to write in. Foreign letters are placed in this part. ES103

  8. Number systems • Decimal 0,1,2,3,4,5,6,7,8,9 • 385 = 3*10² + 8*10¹ + 5*10º • Hexadecimal 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F • 3AF = 3*16² + 10*16¹ + 15*16º • 3AF = 768 + 160 + 15 = 943 in decimal • Binary 0,1 • 1111 = 1*2³ +1*2² +1*2¹ +1*2º = 15 (dec) • 10011010= 1*128+0*64+0*32+1*16+1*8+0*4+1*2+0*1 • =128+16+8+2 = 154 ES103

  9. Conversion to Binary: Integer • Method: divide the number and each successive quotient by 2, noting the remainders. • Decimal Binary Divisions Quotients Remainders 137/2 68 1 least significant bit 68/2 34 0 34/2 17 0 17/2 8 1 8/2 4 0 4/2 2 0 2/2 1 0 1/2 0 1 most significant bit Result (10001001)2 = (137)10 ES103

  10. Conversion to Binary: Floating Point • Method: Multiply the number and each successive fractional by 2, noting the integral part of product. DecBinary Multiplications Product Integral part 0.78125 * 2 = 1.56250 1 most significant bit 0.5625 * 2 = 1.1250 1 0.125 *2 = 0.250 0 0.25 * 2 = 0.50 0 0.5 * 2 = 1.0 1 least significant bit Result (0.11001)2 = (0.78125)10 Note: Stop when 1.0 or repeating itself reached after substraction of integral part. (try 0.6) ES103

  11. Example • Floating point numbers 1101.1101 (8+4+0+1)=13 13.8125 2-4 = 0.0625 0*2-3 = 0*0.125 = 0 2-2 = 0.25 2-1 = 0.5 0.8125 23 22 21 20 ES103

  12. Example Remainders Integral part • 13.6875 conversion into binary form 13 /2 0.685 6 /2 1 x 2 3/2 0 1.3750 1 1 x 2 0.7500 x 2 1.5000 x 2 1.0000 Result: 101.1011 ES103

  13. Binary operations • Addition 1 Carries (Onhand) (71)10 = 1000111 Addend + (36)10 = 0100100 Augend (107)10 = 1101011 1*2º = 1 1*2¹ = 2 1*2³ = 8 1*25 = 32 1*26 = 64 107 ES103

  14. Binary operations • Subtraction 02 02 Borrowings (13)10 = 1101 Minuend - (7)10 = 0111 Subtrahend (6)10 = 0110 Difference Example: 00110 01 1100101001 - 110110110 101110011 1*2¹ = 2 1*2² = 4 6 ES103

  15. Binary operations • Multiplication (10)10 = 1010 x (5)10 = 0101 multiplier (50)10 = 1010 0000 1010 + 0000 0110010 product = 32+16+2 = 50 Note: Addition of each two sub lines are prefferred to prevent potential misstakes. ES103

  16. Binary operations • Division 1010001/11 2 11011 quotient 110010 / 1010 = 101 11) 1010001 - 1010 11 00101 100 • 1010 11 • 001010 100 • 1010 11 • 0000 11 11 00 ES103

  17. Binary operations • Subtraction by “addition with complement” B -A = B+Ā9 –10n+1 where n: number’s power correction complement 878 878 - 539 + 460 339 1338 - 1000 (103) (Truncate) 338 + 1 339 ES103

  18. Binary operations • Subtraction by “addition with complement” Complement : 2-1 = 1 (13) 1101 1101 - (7) 0111 1000 (6) 0110 10101 (Truncate/Shift left) + 1 (Correct) 0110 ES103

  19. There are 2 fundamental types of data: • Program code, which is data, that allows the PC to function. • User data, like text, graphics, sound. • The fact is, that the CPU must have instructions to function. • An instruction is a string of data, of 0s and 1s. The CPU is designed to recognize these instructions, which arrive together with the user input data to be processed. • The program code is thus a collection of instructions, which are executed one by one, when the program runs. Each time you click the mouse, or hit a key on the keyboard, instructions are sent from your software (program) to the CPU, telling it what to do next. • User data are those data, which tells the software how to respond. The letters, illustrations, home pages, etc., which you and I produce, are created with appropriate software. ES103

  20. Both program code and user data are saved as files on the hard disk. Often, you can recognize the type of file by its suffix. Here are some examples: BUT HOW DOES THE COMPUTER RECOGNIZE THESE DATA, OR WHAT TO DO WITH THEM ??? ES103

  21. A drive is the name for several types of storage media. Common to drive medium is: A file system can be assigned to them. They are recognized by the operating system and they are assigned a drive letter. During start up, drives are typically recognized by the PC system software (ROM BIOS + operating system). Thus, the PC knows which drives are installed. At the end of this configuration, the appropriate drive letter is identified with each drive. If a drive is not "seen" during start up, it will not be accessible to the operating system. ES103

  22. Data on any drive are digitized. That means that they are expressed as myriads of 0s and 1s. However, the storage of these bits is done in any of three principles: ES103

  23. HARD DISKS Invented in the 1950s, they were initially capable of storing about 1 Megabyte of data ES103

  24. IBM introduced the first hard disk in 1957, when data usually was stored on tapes. The first 305 RAMAC (Random Access Method of Accounting and Control) consisted of 50 platters, 24 inch diameter, with a total capacity of 5 MB, a huge storage medium for its time. It cost $35,000 annually in leasing fees (IBM would not sell it outright) and was twice the size of a refrigerator. HARD DISKS At the simplest level, a hard disk is not that different from a cassette tape. Both hard disks and cassette tapes use the same magnetic recording techniques. Hard disks and cassette tapes also share the major benefits of magnetic storage -- the magnetic medium can be easily erased and rewritten, and it will "remember" the magnetic flux patterns stored onto the medium for many years. ES103

  25. There are two ways to measure the performance of a hard disk: Data rate - The data rate is the number of bytes per second that the drive can deliver to the CPU. Rates between 5 and 40 megabytes per second are common. Seek time - The seek time is the amount of time between when the CPU requests a file and when the first byte of the file is sent to the CPU. Times between 10 and 20 milliseconds are common. The other important parameter is the capacity of the drive, which is the number of bytes it can hold. ES103

  26. INSIDE A HARD DISK OPENING A HARD DISK RUINS IT, so this is not something to try at home unless you have a defunctional drive. It is a sealed aluminum box with controller electronics attached to one side. The electronics control the read/write mechanism and the motor that spins the platters. The electronics also assemble the magnetic domains on the drive into bytes (reading) and turn bytes into magnetic domains (writing). The electronics are all contained on a small board that detaches from the rest of the drive. ES103

  27. The platters, which typically spin at 3,600 or 7,200 rpm when the drive is operating. These platters are manufactured to amazing tolerances and are mirror-smooth… The arm that holds the read/write heads is controlled by the mechanism in the upper-left corner, and is able to move the heads from the hub to the edge of the drive. The arm on a typical hard-disk drive can move from hub to edge and back up to 50 times per second. In order to increase the amount of information the drive can store, most hard disks have multiple platters. ES103

  28. Data is stored on the surface of a platter in sectors and tracks. Tracks are concentric circles, and sectors are pie-shaped wedges on a track. 4 sides300 tracks/side40 sectors/track512 bytes/sector5,400 rpm rotational speed1 ms track-to-track step time The process of low-level formatting a drive establishes the tracks and sectors on the platter. The starting and ending points of each sector are written onto the platter. This process prepares the drive to hold blocks of bytes. High-level formatting then writes the file-storage structures, like the file-allocation table, into the sectors. This process prepares the drive to hold files. ES103

  29. FLOPPY DISK AND FLOPPY DISK DRIVE The floppy disk drive (FDD) was invented at IBM by Alan Shugart in 1967. The first floppy drives used an 8-inch disk that evolved into the 5.25-inch disk that was used on the first IBM Personal Computer in August 1981. The 5.25-inch disk held 360 kilobytes compared to the 1.44 megabyte capacity of today's 3.5-inch diskette. The 5.25-inch disks were dubbed "floppy" because the diskette packaging was a very flexible plastic envelope, unlike the rigid case used to hold today's 3.5-inch diskettes. ES103

  30. Floppy Disk Drive Terminology Floppy disk - Also called diskette. The common size is 3.5 inches. Floppy disk drive - The electromechanical device that reads and writes floppy disks. Track - Concentric ring of data on a side of a disk. Sector - A subset of a track, similar to wedge or a slice of pie. ES103

  31. The major parts of a FDD include: Read/Write Heads: Located on both sides of a diskette, they move together on the same assembly. The heads are not directly opposite each other in an effort to prevent interaction between write operations on each of the two media surfaces. The same head is used for reading and writing, while a second, wider head is used for erasing a track just prior to it being written. This allows the data to be written on a wider "clean slate," without interfering with the analog data on an adjacent track. Drive Motor: A very small spindle motor engages the metal hub at the center of the diskette, spinning it at either 300 or 360 rotations per minute (RPM). Stepper Motor: This motor makes a precise number of stepped revolutions to move the read/write head assembly to the proper track position. The read/write head assembly is fastened to the stepper motor shaft. Mechanical Frame: A system of levers that opens the little protective window on the diskette to allow the read/write heads to touch the dual-sided diskette media. An external button allows the diskette to be ejected, at which point the spring-loaded protective window on the diskette closes. Circuit Board: Contains all of the electronics to handle the data read from or written to the diskette. It also controls the stepper-motor control circuits used to move the read/write heads to each track, as well as the movement of the read/write heads toward the diskette surface. ES103

  32. WRITING DATA TO A FLOPPY DISK The computer program passes an instruction to the computer hardware to write a data file on a floppy disk. The computer hardware and the floppy-disk-drive controller start the motor in the diskette drive to spin the floppy disk. The stepper motor rotatesaworm-gear shaft in minute increments that match the spacing between tracks. The time it takes to get to the correct track is called "access time." The read/write headsstop at the track. The read head checks the prewritten address on the formatted diskette to be sure it is using the correct side of the diskette and is at the proper track. Before the data from the program is written to the diskette, an erase coil (on the same read/write head assembly) is energized to "clear" a wide, "clean slate" sector prior to writing the sector data with the write head. The erased sector is wider than the written sector -- this way, no signals from sectors in adjacent tracks will interfere with the sector in the track being written. The energized write head puts data on the diskette by magnetizing minute, iron, bar-magnet particles embedded in the diskette surface. The diskette stops spinning. The floppy disk drive waits for the next command. ES103

  33. OPTICAL STORAGE MEDIA ES103

  34. The CD-ROM can be compared to a floppy drive, because the disks are removable. It can also be compared with a hard drive, because of similar data storage capacity. Actually, a CD-ROM disk can hold up to 680 MB of data. This equals the capacity of 470 floppy disks. However, the CD-ROM is neither a floppy nor a hard disk! In the optic readable CD-ROM, the data storage consists of millions of indentations burnt into the lacquer coated, light reflecting silver surface. The burnt dents reflect less light than the shiny surface. A weak laser beam is sent to the disk through a two-way mirror and the sensor registers the difference in light reflection from the burnt and shiny areas as zeros and ones. ES103

  35. The CD-ROM holds one long track, running from the center outwards A 5 km long spiral track holds up to 650 MB data in about 5.5 billion dots (each is one bit). The CD-ROM disk has to read in random pattern. The read head must jump frequently to different parts of the disk. It causes pauses in the read function. That is a disadvantage of the CD-ROM media. Also the faster drives can be rather noisy. ES103

  36. CD-R To make your own CD-ROMs, you use a drive (a “burner”), which can write on special CD-ROM disks. These disks have a temperature sensing layer, which can be changed by writing. You can only write on any given part of these disks once. This CD-R disk is also called a WORM disk (Write Once Read Many). CD-RW The CD-ReWritable (CD-RW) is another type of CD, where you can write multiple times on the same disk surface. However, not all CD drives can read these CDs. To work with CD-RW you need special software (eg Adaptecs). ES103

  37. MEMORY STORAGE The capacities of RAM, cache and other memories are desribed in terms of the number of bytes they can store. RAM : Random Access Memory ROM : Read-Only Memory ES103

  38. 4 1 5 2 3 6 Sequential file (like a magnetic tape) Direct Access / Random Access File (need addressing scheme) ES103

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