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Mathematical Backgrounds
Data is stored in a computer using the Binary System.
The Binary System has two numbers, 0 and 1 The Binary System is used because it is
simple, cheap, and reliable to implement in a computer since 0 can represent a switch being off and 1 can represent a switch being on.
Mathematical Backgrounds (Continued) Two kinds of data are represented in a
computer – numeric values and non-numeric values.
Numeric values are numbers that are used for calculations
Non-numeric values are either letters and other symbols or numbers that are not used for calculations such as phone numbers, SS numbers, etc.
Numeric Representation
Numbers are represented in binary– Explain this on the board
Fixed point or whole numbers are represented one way
Floating point numbers or decimals are represented another way.
Fortunately you don’t have to understand the details
Non-Numeric Representation
Data is stored by codes. ASCII
– American Standard Code for Information Interchange
EBCDIC– Extended Binary Coded Decimal
Interchange Code Unicode
Central Processing Unit
The place where the computing is actually performed
Consists of an arithmetic and logic unit or ALU and a Control Unit
Machine Language
The language that the computer actually understands
Pulse Patterns of zeros and ones.
Storage
AKA Secondary Storage The place where data and programs
are kept on a “permanent” basis. Data and Programs are kept here
when not in use
Memory vs. Storage
Memory is also referred to as Primary Storage.
Storage is also referred to as Secondary Storage.
Stuff stays in memory while it is in use.
Memory is volatile.
Fundamental Concepts Size of Storage
– Bytes, kilobytes, megabytes, … Access Methods
– Sequential– Direct
Physical Devices Used– Disk (Fixed, floppy, removable), CDRom, DVD-
ROM– Magnetic Tape -- cassette, open reel– Flash memory
How a Disk Drive Works
Media Layout– Tracks– Sectors– Disk block– Cluster Size
Logical Layout– Boot record– Directory– Allocation Table
Disk Drive Operation (cont)
Heads Rotation Formatting Write Protection Interface
– IDE– SCSI
Disk Cache
Storage Characteristics Capacity – how much it holds Access speed – how fast the data can be
LOCATED Transfer Rate – how fast the data can be moved
to memory Size – how big is the device Removability – can MEDIA be moved from one
place to another – Can the DEVICE be moved conveniently
Cost Read Write Erase – Which
Capacity How much data can the media hold. 720K up to 100GB is typical of current
computers. My first hard disk cost $770 and had a
capacity of 20mb. My current machine has a disk which I paid
$300 for and has a capacity of 30,000 mb. I can go to a typical retailer such as Office
Max and find a disk of about 40,000 mb for about $100 or less.
Capacity (continued) A CDRom can hold approximately 650mb
of data A DVDRom can hold approximately
17000mb of data A floppy holds 720K, 1.44mb A removable disk holds 100mb or more (I
have one that holds 2200mb and another that holds 120mb)
Flash memory holds 8, 16, 32, 48, 64, up to 256mb
Transfer Rate
How fast the data moved from the disk to the buffer and or memory and or cache
Currently the rate is about 15mb/sec typical with the fastest disks THEORETICALLY near 100mb/sec.
Read Write Erase
Some media such as CDRom cannot have data added to it
Some media such as CDR can have data added to it but it cannot be erased (WORM)
“Most” media can be read, written and erased numerous times.
Compression
A technique for removing redundant data from a data file in order to store it in a smaller space and therefore make it faster to transmit from one place to another
Lossy– JPEG, MPEG, MP3,…
“Lossless”– ZIP, ARC, others