Class Note for CMPSCI 120 at UMass
Class Note for CMPSCI 120 at UMass
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This 5 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at University of Massachusetts taught by a professor in Fall. Since its upload, it has received 20 views.
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Date Created: 02/06/15
1 2 SE 4 5 6 7 8 9D 10 11 12 Computer Basics I Von Neuman architecture The Operating System I The heart of the computer I A large program that starts when the computer is turned on I The OS is needed to run other programs called application programs eg Microso Word I Examples I Microsott Windows XP Vista I Apple Macintosh OS X I Linux The Operating System I Early computers lacked any form of operating system I Later machines came with libraries of support code which would be linked to the user39s program to assist in operations such as input and output I genesis ofthe modernday operating system but machines still ran a single job at a time Runtime libraries became an amalgamated program that started before the rst customer job and could read in the customer job control its execution clean up alter it record its usage and immediately go on to process the next job I 03 became a complete usersystem with utilities applica ions such as text editors and le managers and con guration tools and having an integrated graphical user interface GUI Compilationlnterp retation Why binary I Base representation I au n a n1a2 n1 ak nk where a E01 rI1 Basem1452n2I10 51014I1OZ1I103 2 50 400 10001452 1011 39 I2 1I210I211I23 1 2 0 8 I Basel 11 I Baseg 644B 4I8 481682 4 32 384 420 Binary Adders Moore s Law complexity doubles 2 yrs Bits bytes nibbles words The Central Processing Unit I The CPU has three characteristics I Clock speed I The number ofinstructions he CPU can execute in an amount of ime I Measured in Megahertz MHz GHz I Some imes given in MlPs Moore s Law speed doubles 3 yrs Amdahl s Law The Central Processing Unit I The CPU has three characteristics I Instruction set I The collec ion ofoperations that the CPU can execute I Some instructions are general eg adding 2 integers 13 14 15E 16E 17 I Other instructions are speci c to the type ofCPU I So software that runs on the PC will may not run on the Macintosh and viceversa without emulation I Word size aka data width I The more data that the CPU can potentially manipulate at one time the faster he CPU I The instruction set and the hardware must accommodate large word sizes in order to increase the CPU speed Memory hierarchy I Processor registers I fastest possible access 1 CPU cycle I Level 1 L1 cache I accessed in just a few cycles usually I Level 2 L2 cache I higher latency than L1 by 2to 10x I Main memory DRAM I may take hundreds of cycles I Disk storage I millions of cycles latency but very large I Tertiary storage I several seconds latency can be huge Volatile Storage I Registers I memory that the CPU uses when it executes instructions along with RAM cache I the information goes away when the computer is turned offor restarted shortterm only hundreds of bytes in size 10s of kilobytes often 512 kB or more access times may not be uniform multiple gB I Each program that you run requires some amount of RAM registers amp cache Longterm storage I Hardware that stores I Files that you create I Applications and related data les I The information remains when the computer is turned off I Examples I Hard drive I CDROMCDRWDVD I Flash Drive Virtual memory vs physical memory I Virtual memory is a mapping of real memory topage tables I allowing the physical space to be allocated as is best for the hardware that is usually in noncontiguous blocks and to still be seen as contiguous from a program perspective I allows enlarging the address space to make use of secondary storage that looks to programs like main memory I Programs use the contiguousvirtual addresses rather than real and o en fragmented physical addresses to store instructions and data File Systems I Disk le systems I A disk le system is a le system designed for he storage of les on a data storage device most commonly a disk drive which might be directly or indirectly connected to the computer I Flash le systems I A ash le system is a le system designed for storing les on ash memory devices These are becoming more prevalent as the number of mobile devices is increasing and he capacity of ash memories increase I While a disk le system can be used on a ash device this is suboptimal for several reasons 18E 19 20 21 22E 23 24D 25D Flash memory blocks naye to be expllcltly erased before theycan be rewrltterl Dlsllt le systems are ootlmlzeo to ayolo disk seeks Flash memory oeyloes tend to wear out Wnen a slrlgle block Is repeatedly oyerwntten File Systems I Flat le systems I no subdirectories everything is stored at he same root level on the media I File systems under Mac OS X I Mac OS X uses a le system that it inherited 39om classic Mac OS called HFS Plus wi h Unix permissions added I three kinds oflinks Unixstyle hard links Unixstyle symbolic links and aliases I File systems under Microsolt V ndows I V ndows makes use of the FAT and NTFS le systems I Unlike many other operating systems V ndows uses a drive letter abstraction at the user level to distinguish one disk or partition 39om another For example the path CWIN DOWS represents a directory WINDOWS on the partition represented by the letter C The C drive is most commonly used for the primary hard disk partition on which Wndows is usually installed and 39om which it boots Units of Memory I Kilobytes K 1024 bytes I Megabytes MB 1024 kilobytes I Gigabytes GB 1024 megabytes I Besides the size there are two types of les I ASCII text les contain ASCII characters I Binary les contain characters that cannot be typed on the keyboard generated by sottware Packed ASCII Units of Memory The Internet I internet I a quotnetwork ofnetworksquot that consists of millions of private and public academic business and government networks oflocal to global scope that are linked by copperwires beroptic cables wireless connections and other technologies I Internet I a global system ofinterconnected computer networks that interchange data by packet switching using the standardized Internet Protocol Suite TCPIP I The Internet carries various information resources and services such as electronic mail online chat le transfer and le sharing online gaming and the interlinked hypertext documents and other resources of the World V de Web VWWV Internet Map Networks I LAN Local Area Network I connects network devices over a relatively short distance I use certain connectivity technologies primarily Ethernet and Token Ring InTCPP networklrlg a LAN Is often but not always lmolementeo as a slngle IP subrlet I WAN V de Area Network I spans a large physical distance The lntemet Is tne largest WAN spannlngtne Eartn I a geographicallydispersed collection of LANs I WANs tend to use technology like ATM Frame Relay and X 25 for connec ivity over the longer distances I Router I A network device called a router connects LANs to a WAN I In IP networklrlg the routermall ltall ls both a LAN address and a WAN address Other networks I Mreless Local Area Network I a LAN based on WiFi wireless network technology I Metropolitan Area Network 26E 27 28 29 3o 31 32 33 34 35 I a network spanning a physical area larger than a LAN but smaller than a WAN such as a city A MAN is typically ovmed an operated by a single entity such as a government body or large corporation I Campus Area Network I a network spanning multiple LANs but smaller than a MAN such as on a university or local business campus Other networks I Storage Area Network I connects servers to data storage devices through a technology like Fibre Channel I System Area Network I links highperformance computers with highspeed connections in a cluster con guration eg Cluster Area Network Hierarchy vs hetrarchy The Internet I A characteristic of a heterarchical network is that it is a robust network I If some nodes are removed data can still be sent between nodes I Hierarchical networks do not lend themselves to robustness I The Internet also has dynamic routing where the route ofthe data is determined at the time of transmission based on current network conditions Host Machines and Host Names I Each computer on the Internet is a host machine I Each computer has a unique Internet Protocol IP address such as 124110241 I Some computers have a permanent IP address I Some computers borrow an IP address while they are connected to the Internet I An IP address is not humanfriendly The Growth Of The Internet I In 1983 the Internet connected 562 computers I In 1993 it connected over 1200000 computers I By 1999 on the average a computer was added to the Internet every second I By 2006 the average exceeded ten computers per second I The Internet has experienced sustained growth approximately doubling in size approximately every 10 months I Such growth is called exponential I At any time 39om 1983 hrough 2005 approximately halfthe Internet grow h occurred in the previous 12 to 14 months Internet growth from 1983 to 1991 Internet growth from 1991 to 1999 Internet growth from 1998 to 2005 Host Machines and Host Names I The IP address for most host machines are mapped to a Domain Name Service DNS address in order to be more peoplefriendly I The DNS address consists of a host name followed by a domain name I Example DNS Address mailyahoocom I Host Name is mail I Domain Name is yahoocom Host Machines and Host Names I Each domain name consists of I Institutional site name I Top Level Domain name TLD I Example csumassedu I csumass is the Dept of Computer Science at the University of Massachusetts at Amherst I edu refers to an educational site 36 Host Machines and Host Names Examples ofTLDsinclude com a commercial organization edu a US educational site net anetwork site au Australia fr France hk Hong Kong es Spain 37 Host Machines and Host Names New TLDs have been added as the original set became overloaded While each machine has a unique IP address it can have multiple DNS addresses called aliases Anyone can register a DNS address When you type in a DNS address a domain name server translates it into an IP address
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