Computer and Communication Fundamental

1. Computer and Communication Fundamental Hardware Lecture 11 Shimon Schocken Rina Zviel-Girshin

2. Overview • History of computer development • Basic computer model • Short-term storage: main memory • Long-term storage: disks • Data traffic: the bus • I/O devices: keyboard, mouse, screen, printer • More about OS

3. How Computer Science developed • 1940: The stored program concept was first described in a paper published by Jon Von Neumann • Basic idea: the stored program concepts enables us to designa general purpose machine (hardware) that can execute an infinite number of different programs (software) • Perhaps the most important idea in computer science. The progresspattern of most technologies follows anS-shape

4. The computer world before the stored program invention Square root calculator • Before Von Neumann, hardware and software were fused together • So don’t take the stored program concept for granted! Logarithms calculator Multiplication machine

5. A historical note: Alan Turing and the Enigma • It is quite likely that World War II could not be won without Alan Turing.

6. The Basic Model (Von Neumann, 1940)

7. The basic model -- scaled up to a typical PC architecture

8. Short-term storage: main memory • Internal short-term storage areas in the computer: main memory. • Real main memory: typically 64-256 MB. This is the amount of information the computer can process at any one time. • Main memory is physically implemented in banks of transistors called microchips. These chips are plugged into the motherboard • Main memory is also called RAM (Random Access Memory) . That is, any byte of memory can be accessed without touching the preceding bytes. • The term RAM is synonymous with main memory - the memory available to programs. • For example, a computer with 8M RAM has approximately 8 million bytes of memory that programs can use.

9. Main memory

10. Main memory (cont.) • Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents. As soon as the power is turned off, whatever data was in RAM is lost. • Part of the RAM is ROM (Read Only Memory). • ROM holds basic instructions for starting up the computer. Unlike RAM, ROM cannot be written to. • Main memory also provides buffers for all the I/O devices:video buffer, keyboard buffer, disk buffer, etc. • Why do we need buffers? Because the CPU is much faster than the I/O devices. More about this, later • The memories (buffers) associated with the I/O devices are typically stored either inside the devices (e.g. keyboard, printer, disk controller) or on extension boards (e.g. video board).

11. Long-term storage: disks • The word storage is used for memory that exists on tapes or disks. • Disk is a round plate on which data can be encoded. • There are two basic types of disks: magnetic disks and optical disks. • On magnetic disks, data is encoded as microscopic magnetized needles on the disk's surface. • You can record and erase data on a magnetic disk any number of times. • Magnetic disks come in a number of different forms: • Floppy disks • Hard disk • Removable cartridges

12. Optical disks • Optical disks record data by burning microscopic holes in the surface of the disk with a laser. • To read the disk, another laser beam shines on the disk and detects the holes by changes in the reflection pattern. • Optical disks come in three basic forms: • CD-ROM - most optical disks are read-only. That means you can read the data from a CD-ROM, but you cannot modify, delete or write new data. • WORM - stands for write-once, read-many. WORM disks can be written on once and then read any number of times. You need a special WORM disk drive to write data onto a WORM disk (CDRW). • EO – erasable optical - EO disks can be read to, written to, and erased just like magnetic disks.

13. Disk storage

14. Hard Disk Anatomy • The disk is divided to tracks and sectors; Each sector holds one block of data, with a pointer to the next block in the file • The file allocation table (also stored on the disk) associates between file names and the address of the first block in the file

15. Anatomy of disk formatting • Before a disk can be used, it must be formatted • The formatting program (utility) creates the logical blocks, by marching through the tracks and writing “end of block” markers, which is simply a special bit pattern • The formatting operation also creates the free list.

16. Anatomy of opening a file (or starting a program) • Each file is scattered on several physical blocks which may or may not be adjacent (why?) • When the user opens a file, or starts a program, the O/S follows the pointers and loads the file into main memory • Thanks to the O/S, we don’t have to worry about how the disk is managed. A file is a file is a file.

17. A real hard disk

18. Typical disk storage devices floppy disk hard disk ZIP disk CD ROM disk 1-2 MB 10 GB (10,000 MB) and up 100 MB 500 MB - 4 GB • A single disk can contain anything from a few files to thousands of files, depending on the disk’s capacity

19. More about magnetic disks • Floppy disks: A typical 5¼-inch floppy disk can hold 360K or 1.2MB. 3½-inch floppies normally store 720K, 1.2MB or 1.44MB of data. • Hard disk: Hard disks can store anywhere from 20MB to more than 10GB. Hard disks are also from 10 to 100 times faster than floppy disks. • Removable cartridges: hard disks encased in a metal or plastic cartridge, so you can remove them just like a floppy disk. Removable cartridges are very fast, though usually not as fast as fixed hard disks.

20. Data traffic: the bus • Computer bus is a collection of wires through which data is transmitted from one part of a computer to another.

21. The bus • You can think of a bus as a highway on which data travels within a computer. • Computer bus connects all the internal computer components to the CPU (Central Processing Unit ) processor and main memory. • All buses consist of two parts • an address bus • a data bus. • The data bus transfers actual data. The address bus transfers information about where the data should go. • The size of a bus, its width, is important because it determines how much data can be transmitted at one time. • For example, a 16-bit bus can transmit 16 bits of data in one shot.

22. The bus • Every bus has a clock speed measured in MHZ (megahertz). • A fast bus allows data to be transferred faster, which makes applications run faster. • In networking, a bus is a central cable that connects all devices on a local area network (LAN).

23. Input / Output devices • I/O and devices can be connected to the basic machine via multiple ports (instead of the two elementary input/output ports).

24. The keyboard

25. Keyboard anatomy • The keyboard has a built-in processor that converts key-strokes to ASCII values. These values are stored in the keyboard buffer. • Various programs (like Word), “visit” the keyboard buffer every once in a while and pick up the stuff that they find there (event handler routines).

26. The screen

27. Screen anatomy • The display unit is hooked to the video buffer, which stores ASCII codes. Using a character generation table, the display unit can paint various shapes on the screen. • Bit map graphics is a very similar idea, only the details are different.

28. Real screen (RGB)

29. The printer

30. The printer • Printer is a device that prints text or illustrations on paper. • There are many different types of printers. • Logically speaking, the printer operates similarly to the screen, using bitmap tables to transform ASCII values to ink patterns on paper.

31. The Operating System • We have covered a lot of ground, and described all the major hardware components of the computer. • Obviously, we need someone to manage all these resources – OS (Operating System). • For obvious reasons, the OS is a gigantic computer program. • Windows 2000, Windows XP = 40 millions lines of code!

32. The Operating System: typical tasks • The O/S is a huge computer program that acts like a resource manager: • Disk management • Files (and directory) management • Memory management • I/O device management • Multitasking • GUI management • Events management • Communications management • … And many more less important tasks • At any given point of time, only a small part of the OS runs on the computer. • The other parts sit on the disk, and are loaded into memory as the need arises.

33. Connectivity: no computer is an island

34. Networked computers - step 1 A bunch of stand alone computers and peripherals

35. Networked computers - step 2 Putting a network backbone

36. Networked computers - step 3 Installing network interface cards

37. Networked computers - step 4 Connecting the machines to the LAN backbone

38. Network topology • A group of two or more computer systems linked together.

39. That’s all, folks! Any questions?