3.3 Computer Systems

1. Cristian Hill 3.3 Computer Systems

2. 3.3.1 Define Operating System • A collection of programs which deal directly with the hardware system and sub-systems, provide user interfaces and log the activates taking place in the system. • Examples: Linux, MacOS, Windows, Novell Netware

3. 3.3.2 Operating System Functions

4. Peripheral Communication • Peripheral Devices are all hardware outside the CPU • Only deals with data coded into binary machine code (See section 3.5.9 for exception) • The OS keeps track of the device drivers and signals if they are not working correctly • Drivers are software designed to interface directly with the hardware • The OS provides a standard interface between hardware devices and applications. • The App can the us a <print> type instruction with in the high-level language rather than low level commands

5. Coordinating Concurrent Processing • Concurrent processes are processes or jobs running on the system the entire time the computer is on • The OS handles the loading and unloading of these processes to and from primary memory Note: “The curious user can get a list of these processes – although it won’t always mean much to the un-initiated” p. 161

6. Memory Management • The OS ensures that each process runs in its own (virtual) memory space • It also ensures that each memory space does not change memory belonging to another process…in theory

7. Resource Monitoring • Running processes are allocated resources by OS • E.g. Processor time and memory needed • This is an attempt to keep all processes running • “It doesn’t always work, you may have noticed” p.161

8. Accounting and Security • Multi-user, networked, OS’s have to make sure that only registered users can get access • A manager controls this via OS functions • Logs kept of the activities of the users my be huge buy necessary if security or other problems arise • By following the audit trail kept by the accounting software you can discover activities of unauthorized users

9. Program and Data Management • This includes some of the functions already described • The files, ports and other data resources a particular programs is using to read and write information must be kept by the OS • If not one program may write another one’s files • Data transfer and/or program instructions from files to the primary memory is handled by the OS

10. 3.3.3 Characteristics of Computer Systems and a Comparison of These and Applications of Different Computers

11. Computer Systems • Made of input, processing and output-communication hardware devices • As well as the software required to operate and connect these devices so they can function • May be small and only a single computer (PC) or of large numbers of computers linked together in a network • May also vary in size of secondary storage and memory, processor speed and OS loaded • PC generally allow for ‘multi-tasking’

12. Cont’d Input Devices-mouse, keyboard, scanner Processor Unit – processor, primary memory and control unit Output Devices – printer, modem Secondary Storage – Hard drive System Software – OS Application software - accounting package Input devices Processor Unit Output Devices Secondary Storage Data System Software Application Software Stored Loaded

13. Personal and Portable Computers • PC’s are also called microcomputer • Typically has a CD or DVD drive, keyboard, mouse and monitor, and other wrong information • Laptops are similar to PC but can run off of batteries for 2-6 hours • Typical cost range: $2,000- $10,000 • I/O devices are connected via serial and parallel ports Note: The book says that USB is a recent development…it came out in 1996, book was published in 2004.

14. Mainframe Computers • Designed to run a range of application software and process large volumes of transactions for many users at once • Not uncommon for a mainframe computer to have thousands of users at once • Considerable more amount of RAM and cache • Contains multiple processors and are often run in parallel • Uses a high capacity disk configuration (aka disk farm) • Can store TB of data

15. Cont’d • Cost range in millions of dollars • Traditionally physically large and need own rooms with expensive air cooling systems

16. Super Computers • Runs very complex tasks that require large amounts of processor time • The US Weather Bureau super computer’s primary memory ( RAM and ROM) is 4 GB in size

17. Multi and Single Users Computer Systems • PC = single user • Multi-User computers need to be able to handle a large number of users logged on simultaneously • Users are connected via dumb terminal or PC • Dumb terminals do not do any processing

18. Comparison • Single User System • Multi User System Single User CPU Single CPU which shares time between users and other processes User 1 User 2 User 3 User 4 User 5 User 6

19. 3.3.4 Comparison and Different Applications of Computer Systems

20. Instructions • Keep in mind these characteristics: • Primary store size (RAM), backing store size (online disk and tape capacity), I/O device range, physical size and cost, type of operation, and processor word length and speed

21. Personal and Portable Computers • Designed to support individuals at home or work • Typically allows user to create, store, retrieve and print word processed documents, connect to Internet, and access to email • Are powerful and can perform complex financial calculations and graphical applications

22. Mainframe • Much more costly than PC • Handles a number of simultaneous users • RAM, cache and disk size are greater • Used primarily by banks, government departments and insurance agencies • Focused on handling enormous volume of transactions

23. Super Computer • Even more expensive than the mainframe or PC • Faster processor speed • Often uses 100s of PC’s in parallel • Large amounts of RAM and cache • Used to run single computer models such as a model to predict weather

24. 3.3.5 Computer System Operation Modes

25. “Computer systems operation is controlled by the operating system and the desired mode of operation” (166) • Other examples of operation modes • Real Time Processing • Interactive On-line • Batch Processing

26. Real Time • Embedded into equipment and have the basic characteristics of larger Systems • Are pre-programmed to act on inputs without need to alert operator • Thus time between input and action is reduced • VCR’s and heart monitoring use these systems Go VCR’s, thou shalt never die

27. Interactive On-line • Very common • Used in most databases • Operator interacts with the program by connecting directly to it

28. Batch Processing • With this there is a time gap between data collection and data processing • Used to perform a set of processing steps on a set of data that has been collected over time

29. 3.3.6 Applications of Different Modes of Operation

30. General comparisons • Real time is usually found in embedded chip technology • The major issue is that they are required to operate without human intervention • Online systems operate where it is important that the user has access to the functions of the System • Batch processing is used where all processing takes place at once

31. 3.3.7 Relationship Between Master File and Transaction File

32. ♥Relationships♥ • The master file contains the main data for a computer system or application • The transaction file holds a list of changed needed to be made to the master • These changes are called transactions • In batch processing the data in the master file may not be up to date

34. 3.3.8 Reliability of Systems

35. Integrity • The correctness of the data is described as its integrity • The more complex and autonomous the more mistakes • Multiple systems may be ran in parallel where failure may be catastrophic

36. Threats to Data • Unauthorized users may gain access and alter or remove data • Physical media may be stolen (discs, tapes, etc. ) • Hardware and backups may be stolen • Fire or flood damage Lions and tigers and bears, Oh my

37. Protection • Passwords and privileges can be used to prevent data from being altered • Passwords must be of reasonable length and hard to guess • Usually 6 or more characters • “not your partner’s, child’s, dog’s, parakeet’s name” p. 169 • When data is transmitted over a network it may be encrypted if especially sensitive

38. Cont’d • Encrypting data helps ensure that if it is accessed it is not readable • A PIN number on the magnetic strip of a bank card is encrypted for this reason

39. Backup Strategies • Backup copies are kept in a safe place, usually in a different building • Backup copies are user to restore a system to the state existing at the last backup.