How to Interpret the Contents of Stored Memory Data
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Memory stores data as voltages that are interpreted as binary 0s and 1s. Combinations of 0s and 1s represent numeric, alphabetic, and other data types depending on the coding standard used. ASCII and Unicode are common coding standards that assign numeric codes to letters, punctuation, and other characters. An operating system like DOS or Windows provides an interface to interpret commands and access stored data, sitting on top of lower-level components like the BIOS that initialize hardware and load the operating system at startup. File systems then organize and control how application data is stored and retrieved from memory devices using files with standardized naming conventions and extensions.
![A.S.C.I.I. Coding
There are 255 characters available to 8 bits. 0 isn't used.
Only the numbers from 32 to 126 (20 to 7E hex) are defined as
*printable* characters (the others are defined as control codes)
0 1 2 3 4 5 6 7 8 9 A B C D E F
---------------------------------
2 | ! " # $ % & ' ( ) * + , - . /
3 | 0 1 2 3 4 5 6 7 8 9 : ; < = > ?
4 | @ A B C D E F G H I J K L M N O
5 | P Q R S T U V W X Y Z [ ] ^ _
6 | ` a b c d e f g h i j k l m n o
7 | p q r s t u v w x y z { | } ~](https://image.slidesharecdn.com/cpukgdhsfqfkohnckopt-signature-cd8ecd5b5dfde0a3b303daa66c44856412c9d6cb2cd34514d68cefadeef76e9a-poli-150905074055-lva1-app6891/85/How-to-Interpret-the-Contents-of-Stored-Memory-Data-4-320.jpg)
![Web URLs use hexadecimal encoding
• All URLs address filespace on a web server.
• All URLs obey Unix filenaming rules.
• All Windows web servers obey Unix filenaming rules.
• There are no exceptions at all.
• All URLs that use Windows filenames have to be 'repaired' using URL encoding before
they work on the web.
'What are those "%20" codes in URLs?'
http://www.blooberry.com/indexdot/html/topics/urlencoding.htm
"...Only alphanumerics [0-9a-zA-Z], the special characters "$-_.+!*'()," [not including the
quotes], and reserved characters used for their reserved purposes may be used unencoded
within a URL."
http://www.w3schools.com/tags/ref_urlencode.asp
Spaces are converted into plus (+) signs or %20 to avoid semantic ambiguities.
Special characters or 8-bit values are converted into their hexadecimal
equivalents and prefaced with a percent sign (%).](https://image.slidesharecdn.com/cpukgdhsfqfkohnckopt-signature-cd8ecd5b5dfde0a3b303daa66c44856412c9d6cb2cd34514d68cefadeef76e9a-poli-150905074055-lva1-app6891/85/How-to-Interpret-the-Contents-of-Stored-Memory-Data-16-320.jpg)
How to Interpret the Contents of Stored Memory Data
- 1. How to interpret the contents of stored memory data
- 2. Memory cells store voltages - Interpreted as 0 or 1 Combinations REPRESENT numeric data ie. Letters, numbers, punctuation marks, graphics characters Memory is not restricted to using numeric coding Bytes can represent: ● CPU Instruction codes ● alpha numeric characters (word processors) ● pure binary No's It's all down to interpretation with the software application.
- 3. ASCII AMERICAN STANDARD CODE FOR INFORMATION INTERCHANGE Original ASCII, 128 codes (0 to127) represented. ASCII is a coding standard which means that data is stored according to the ascii standards rules. • English alphabet • punctuation • control codes Each keyboard key has an ASCII code assigned
- 4. A.S.C.I.I. Coding There are 255 characters available to 8 bits. 0 isn't used. Only the numbers from 32 to 126 (20 to 7E hex) are defined as *printable* characters (the others are defined as control codes) 0 1 2 3 4 5 6 7 8 9 A B C D E F --------------------------------- 2 | ! " # $ % & ' ( ) * + , - . / 3 | 0 1 2 3 4 5 6 7 8 9 : ; < = > ? 4 | @ A B C D E F G H I J K L M N O 5 | P Q R S T U V W X Y Z [ ] ^ _ 6 | ` a b c d e f g h i j k l m n o 7 | p q r s t u v w x y z { | } ~
- 5. ASCII has been extensively enhanced. Modern systems use Unicode, which is a 2- byte 16-bit system.
- 7. HOW DATA IS MANIPULATED AND CONTROLLED Disk Operating Systems
- 8. DOS provides the prime means of interaction between the user and the computer hardware. The command interface (DOS prompt) converts keyboard commands into instructions understood by the machine hardware. Without DOS there is no means of interpreting input commands. The GUI "sits" on top of DOS and provides a graphical equivalent of keyboard commands. Windows - written by Microsoft for PC's. UNIX and UNIX clones, eg. Linux, Apple http://en.wikipedia.org/wiki/Operating_system http://upload.wikimedia.org/wikipedia/commons/7/77/Unix_history-simple.svg
- 9. HOW THE OPERATING SYSTEM IS STARTED THE BOOT PROCESS Turning on the POWER switch ("Cold start") Simultaneously pressing CTRL, ALT and DELETE ("Soft start") The boot process is controlled by the Boot ROM, located on the motherboard, which contains part of the BIOS. Functions of Boot ROM: ● Checks hardware ● RAM check ● Looks for a boot disk
- 10. The Boot Loader • The BIOS loads into memory the program residing in the first sector of the boot device, called the Master Boot Record or MBR. • The MBR is only 512 bytes in size and contains machine code instructions for booting the machine, called a boot loader, along with the partition table which holds the information on how the partitions, containing file systems, are organised on the drive. • Once the BIOS finds and loads the boot loader program into memory, it yields control of the boot process to it, from which the operating system can be located and run up. http://en.wikipedia.org/wiki/Master_Boot_Record http://en.wikipedia.org/wiki/Booting#Modern_boot_loaders
- 11. The File System A file system controls how data is stored and retrieved. The data is stored individually and named, called a "file". The structure and logic of the file storage is called a "file system". There are dozens of different systems available, and unassociated operating systems use unrelated file systems. For instance, • MS Windows uses NTFS • Linux uses ext4 Among the most important aspects of filesystems is understanding how filenames and access permissions are treated on the two most common OS's, ie. MS and UNIX / Linux
- 12. Comparison of filenaming conventions UNIX Files | Windows files -------------------------|---------------------------- 256 characters filename | 256 character filename filename.ext.ext.ext | 3 character extension sensitive to case | not sensitive to case Windows: k:drivespace Unix: /home/user/webspace/images WWW: http://news.bbc.co.uk/1/hi/sci/tech/default.stm Note: Internet web URLs follow Unix filename conventions
- 13. Microsoft file names Older MS-DOS formatted filenames can contain no more than 8 characters, and these must not contain any command characters. MS Windows now allows long file names and control characters to be used.
- 14. File extensions ● The file name is followed by a dot . which separates it from its extension. ● The file extension is 3 characters long and describes the type of file. *.COM - Command file. Runs from the DOS prompt. Small file =<64 KB *.EXE - Executable file. Larger file >= 64 KB *.SYS - System file. Installed in memory using an installation program. *.BAT - Batch File. Contains series of text commands batched together. Other extensions are produced typically by application software for their data files, eg .doc, .html, etc. (The * is used here to represent any filename)
- 15. It is bad practice to use control characters in a file name.. When transferring files to INTERNET systems, the filenames should be re-formatted to comply with UNIX standards. No character is allowed which the system uses for commands or other functions, such as , /, ., etc. The underscore character _ is accepted as a separator as a space must not be used. URL encoding is needed if a filename and path contains control characters.
- 16. Web URLs use hexadecimal encoding • All URLs address filespace on a web server. • All URLs obey Unix filenaming rules. • All Windows web servers obey Unix filenaming rules. • There are no exceptions at all. • All URLs that use Windows filenames have to be 'repaired' using URL encoding before they work on the web. 'What are those "%20" codes in URLs?' http://www.blooberry.com/indexdot/html/topics/urlencoding.htm "...Only alphanumerics [0-9a-zA-Z], the special characters "$-_.+!*'()," [not including the quotes], and reserved characters used for their reserved purposes may be used unencoded within a URL." http://www.w3schools.com/tags/ref_urlencode.asp Spaces are converted into plus (+) signs or %20 to avoid semantic ambiguities. Special characters or 8-bit values are converted into their hexadecimal equivalents and prefaced with a percent sign (%).
- 17. Windows drive storage The DOS system uses drive letters, such as a: and b: for floppy disk drives c: for the hard disk drive d: or e: for a CD-ROM drive f: onwards for network drives |_ a:____ |_ b: |_ subdirectories |_ c: |_ |_ d: |_ |_ e: |_ f:____ |_ |_ subdirectories