how to count in binary
finger party trick

add two binary numbers

not just how a number is encoded
some sense of how the CPU, that is ALU
handles addition (of binary numbers)

ASCII - american standard code for information interchange

http://www.asciitable.com/
internally, letters are stored as numbers
capital A is 65
lowecase A = 97
digit 0 is 48

regular ASCII goes from 0 to 127
2^7 possible values
can store it in 7 bits

extended ascii code
a Text file, if ASCII, usually is one byte per "letter"

File extensions
stuffbeforethedot.extension
used to be:
8chars.3le -- three letter extension

this is from the days of DOS (early DISK OPERATING SYSTEM)

.EXE is a three letter extension meaning executable

.XML

.HTM

.DOC
.XLS
.MDB
.PPT

backwards compatibility

cmd - command prompt
text-based interface to the Operating System
DOS
DOS prompt

Office 2007, longer file extensions
.DOCX
.XLSX
.ACCDB
.PPTX

Tools/Folder Options/View Tab
hide extensions for known file types

Windows uses GUI -- pronounced "gooey"
graphical user interface

Old way: to open a document: first open program. then, file/open and specify the file

New way: file associations. based on the extension part of the filename, Windows knows what program to open.

ASCII is not the only encoding. There is also Unicode.
since greater range, file size will be greater. if 4 bytes per letter, X 4 to get file size