TextNotes - Bits-Bytes-Storage
The Primary storage area of the computer is R.A.M. ( Random Access Memory ) This is the "working" memory of the computer. RAM is measured in Bytes. 64 megabytes, 256 mb, etc.
Secondary storage = everything else such as a floppy disk, hard drive, tape, cartridge, nintendo cartridge, CD-ROM disk, smart cards.
There are two major types of storage at this time:
Magnetic and Optical:
Magnetic storage uses small particles of Iron Oxide ( rust ) on a plastic surface. These particles are arranged by an electromagnet .
Magnetic - floppies: 5.25 inch , 3.5 inch,
Hard drives are where your programs and data are stored until you call them up: They are measured in GIGABYTES, ( How much data they can hold ) -3gig - 6gig - 10gig - 50 gig.
Optical storage uses a LASER to etch pits on the surface of a plastic disk.
Optical storage ( cd-rom, dvd ) is more efficient than magnetic storage:
A CD holds 600 megabytes per disk compared to 1 megabyte for a floppy.
Music cd’s contain digital information therefore they can be read by the computer.
Laser disks are exactly the same as CD-ROM but larger.
Since secondary memory used to be expensive, data compression techniques were developed to save space. These were called data compression utilities.
Ex; stacker, super space, double space, etc.
Do NOT ever use these !!
Retrieval rates are important (remember that
speed is power)
A floppy drive reads and writes slower than a hard drive.
Cd - rom drives are measured by their transfer rate ( how fast they can get information from the disk to the processor ) 16x, 32x, 50x).
All secondary storage drives must go through an interface card before the information gets to the computer. There are two types of cards:
IDE=(integrated drive electronics) -runs one or two drives.
SCSI=(small computer system interface) up to seven drives.
All storage devices fall into one of these two categories:
Sequential access: must be accessed in order. Ex: cassette tape-reel to reel. These are used for long term storage.
Random access: any order, ex: floppy drive, CD-ROM. These are usually used for short term storage.
Other storage devices:
Smart cards are now available- adv/disadvantages.
Should smart cards be used to contain a persons personal information? Health information?? Employment information??
Should they be used as debit cards? Would you??
How does the drive save my file ???
We can communicate with each other by using only zeros and ones. If we assigned 8 characters to each letter, we would get:
01010101 = h
10101010 = e
10001010 = l
10001010 = l
00101010 = o
When you type a word into a processor, it is being received by the computer as thousands (millions) of zeros and ones.
10110101 10110101 10111001 10100011 10110010 11000101 etc...
ASCII CHART
Character
Binary Code
0
00110000
1
00110001
2
00110010
3
00110011
Other Miscellaneous Characters:
!
00100001
"
00100010
#
00100011
$
00100100
%
00100101
&
00100110
'
00100111
(
00101000
)
00101001
*
00101010
+
00101011
,
00101100
/
00101111
-
00101101
:
00111010
;
00111011
<
00111100
=
00111101
A
01000001
B
01000010
C
01000011
D
01000100
X
01011000
Y
01011001
Z
01011010
a
01100001
b
01100010
c
01100011
d
01100100
e
01100101
f
01100110
Period
00101110
Comma
00101100
Space
00100000
One character = 1 byte = 8 bits
Kilobyte = approximately 1000 bytes
Megabyte = approximately 1 million bytes
Gigabyte = approximately 1 billion bytes
Magnets have to poles "+" and "-". These are the same as 0 and 1.
0 0 1 0 1 0 0 0 = + + - + - + + +
As the diskette spins, the particles are
lined up to match the data.
This is why you do not want to place your
diskette near a strong magnet.
Optical storage does exactly the same thing. It uses a laser to etch pits/no pits on a piece of plastic.
Ram is measured by how many megabytes it can hold. 16mb of ram can hold 16 million bytes.
Hard drives are measured by how many bytes they can hold (1.2 gigabyte hard drive).
Drive Tolerances are very small:
HOW IS A PICTURE SAVED ??
One method used to understand this is to imagine a "GRID" being placed over the image.
A typical picture is 50 kilobytes in size.
50 kb = 50,000 bytes = 450,000 bits that must be sent to download a black/white picture.
Color pictures must also have the color of each square (
color pictures are usually 8 times larger than b/w.)