Understanding Computer Memory Fundamentals

Computer Memory
 
 
Memory is made up of semi-conductor switches. The
position of the switch (open or closed) is used to
represent the binary numbers 0 or 1.
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Slide
2
 
 
Bit:
 From 
B
inary dig
it
Smallest unit of information computer can process
Can have one of two values: 0 or 1
A single unit of memory is called a BIT and can store 0 or 1.
Two BITS together allow 4 different binary numbers to be
stored: 00 , 01 , 10 or 11.
Eight BITS can store 256 different numbers:
00000000 through to 11111111
Byte
Collection of 8 bits
Can represent 256
different messages
(256 = 2
8
)
Bit Basics
Slide
3
 
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Slide
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Why is ROM needed in a computer?
Slide
5
 
When a personal computer is in use the following are
copied into RAM from the backing storage:
The Operating System (OS)
All the other programs that are running
Any data files that are in use.
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Why is RAM needed in a computer?
Slide
6
 
Memory is linked to the CPU by two different types of
BUS, the address bus and the data bus (
a BUS is a set
of very thin parallel wires that transmit binary data
).
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The DATA BUS is then used to transfer the contents of
the memory address (
the data
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location and the CPU (
and visa-versa with RAM
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How is memory accessed
Slide
7
 
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This is because secondary storage (
such as a hard drive
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would be far too slow for the CPU.
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This will significantly slow the rate that the computer can
process instructions and data.
 
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How does the amount of RAM affect performance?
Slide
8
 
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However, at any one time only some blocks of the data in RAM are actively being used by
the CPU so it is possible for the 
OS
 to copy blocks of inactive data from RAM to the hard
drive and copy active blocks of data into RAM to be accessed by the CPU.
To the CPU, it therefore appears that all the programs are running from RAM and each
program behaves as if it had as much RAM as it needed, hence the term virtual memory.
This solution is a very cheap but does have its limitations.
Because the hard drive is so much slower than RAM, this swapping of inactive and active data blocks
will cause a slight delay as the computer switches tasks.
If a computer is very low on RAM or accessing many different areas of memory then it will slow down
dramatically because too much time will be spent swapping blocks of data between real and virtual
memory.
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Slide
9
 
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If the CPU needs to access a memory
address it first checks the cache memory
to see if there is a match. If there is then it
access the contents of the cache version.
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10
 
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A CPU with a larger cache memory and more levels of cache
memory will have a higher performance than one without cache
memory.
 
Flash memory is a special type of RAM that, unlike normal RAM, is non-
volatile (
it does not need a power supply to preserve the memory contents
).
Flash memory cannot however replace RAM in a computer as the
read/write speeds are too slow.
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Compact Flash™ and Secure Digital™ (
SD
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USB memory sticks.
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Slide
11
 
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.
How are changes in memory technologies leading to innovative
computer designs?
Slide
12
Different types of Memory
Slide
13
1) RAM
 stands for 
Random-Acess Memory
. It means that the CPU
(Central Processing Unit) can 
directly
 access any address location of
RAM memory.  Thus, 
RAM
 is a quickly accessible memory of the
computer. But it stores the data 
temporarily
.
2) RAM
 is a volatile memory. It means that it loses the data stored in it
when the power is turned off.
3)
 The programs that the CPU requires during the execution of any
program are stored in this memory.
4)
 It is the 
fastest
 and also the 
costliest
 memory of a computer. It is
read-write
 memory of the computer. Thus, the data in RAM can
be 
modified
.
5)
 It is further classified into two types – 
SRAM
 (Static Random Access
Memory)
 and 
DRAM
 (Dynamic Random Access Memory)
.
a) 
SRAM i.e. the 
Static RAM
 requires the constant flow of
the 
power/electricity
 to retain the data inside it.
b) 
DRAM i.e. the 
Dynamic RAM
 needs to be refreshed to retain the
data it holds.
What is Random-access Memory?
Slide
14
Comparison between DRAM and SRAM
Slide
15
1) ROM
 stands for 
Read-Only Memory
. The CPU 
can not
directly
 access the ROM memory. The data is, first,
transferred to RAM and then the CPU can access that data
from the RAM.
2) ROM
 is a 
non-volatile
 memory. This means that the data
inside it retains even if the power of the CPU is switched off.
3) 
This memory stores all the crucial information essential to
operate the system, like the program to boot the computer.
4) 
ROM is generally used in 
Embedded systems
 such as
calculator, peripheral devices, etc.
5) 
It is further classified into 3 types – 
PROM
EPROM
,
and 
EEPROM
.
What is ROM?
Slide
16
1) PROM
 – It stands for 
Programmable read-only memory
.
Once the user has programmed it, the data and instructions
in it cannot be changed.
2) EPROM
 – 
Erasable Programmable read-only memory
. It
means that it can be reprogrammed. In order to erase data
from it, we need to expose it to ultraviolet light. After that,
the user can reprogram it again,
3) EEPROM
 – 
Electrically erasable programmable read-only
memory
. To erase the data we need to apply an electric field,
unlike the EPROM where we needed ultraviolet light. But we
can only erase only portions of the chip.
Types of Read-Only Memory
Slide
17
Differences between RAM and ROM
Slide
18
Memory Unit
Slide
19
DAS: 
DAS solutions are typically the simplest and the cheapest.
High capacity backup hard drives, solid state drives, and optical
disc drives are all examples of DAS solutions. Because of the
relatively cheap price and minimal space obstruction, DAS is a
great choice for very small businesses with only a handful of
employees. Remote access is usually not possible with DAS.
Picking the Best Data Storage Solution
Slide
20
NAS: 
Small to mid-size companies have more demanding
data storage requirements than small businesses. NAS
allows these companies to store data in a centralized
location, and can be accessed remotely from various devices
on your network. NAS are usually pieces of hardware fitted
with multiple hard drives in a RAID configuration, and can
be connected to a switch or router on a network via a
network interface card. If your business is looking for
centralized storage, remote access, file sharing, and
scalability, consider utilizing a NAS solution.
Picking the Best Data Storage Solution ……. Contd.
Slide
21
SAN: 
SAN solutions are a good fit for large companies and
enterprises that have the space to store multiple disk arrays,
switches, and servers. SAN gives access to large blocks of
data between servers and storage devices across multiple
locations. This solution is a necessity for any large company
that needs to reliably and quickly access massive amounts
of data. SAN also provides a higher level of data security and
is much more fault tolerant than NAS and DAS.
Picking the Best Data Storage Solution …….. Contd.
Slide
22
Secondary storage is also called external, secondary or
auxiliary memory. This type of storage holds data for the long
term. Data stored on secondary storage devices can only be
removed by deleting it. Secondary memory is where the
operating system, hardware drivers and data created by the
user is kept and stored permanently.
This means that, in the case of power failures, secondary
storage will preserve the information that is saved to it, even
if the power to the computer is lost, while the data on the
primary storage devices will be lost.
The most common example of secondary storage is the hard
drive inside a computer. Other examples include solid-state
drives (SSDs), USB flash drives and secure digital (SD) cards.
SECONDARY STORAGE
Slide
23
Comparison: Memory versus storage
Slide
24
One purpose of storage devices is to back up or 
archive
 your
important data. In the business world, there is a need to
store data permanently and in a way that does not get
destroyed, corrupted or damaged easily. Different types of
storage media can be used for backing up or archiving.
Backups are records of important information that is used
often. Backups are kept for a relatively short period of time.
STORAGE MEDIA FOR BACKUP
Slide
25
Stores information
Non-volatile, permanent storage
Characteristics
Media
Capacity
Access time
Secondary Storage
Slide
26
Types widely used today
Floppy disks
Hard disks
Optical disks
Magnetic tape
Types of Storage Media
Slide
27
Portable and removable
Flat circular Mylar media
Magnetic charge on metal
oxide film coating
Standard 2HD 1.44 MB
Parts
Tracks
Sectors
Floppy Disks
Slide
28
Floppy disk cartridges
Zip Disks
250 MB
SuperDisks
120 MB
HiFD disks
200 MB
High Capacity Floppy Disks
Slide
29
Metallic disks
Fast retrieval, greater capacity
Read/write heads ride cushion of air .000001” thick
Three types
Internal hard disk
Hard-disk cartridge
Hard-disk pack
Hard Disks
Slide
30
Inside system
unit
Non-removable
or portable
Great capacity
Upto 2 TB
Fast access
speed
Internal Hard Disk
Slide
31
Portable, removable
Complement internal
hard drive
Hard-disk Cartridges
Slide
32
Used in mainframes
Removable
Resemble stack of
vinyl records
Multiple read/write
heads
Massive storage
capacity
Fast access time
Hard-disk Packs
Slide
33
Improving performance of hard disks
Disk caching
R
edundant 
A
rrays of 
I
nexpensive 
D
isks (RAID)
File compression and decompression
Performance Enhancements
Slide
34
Very large capacity
Up to 17 gigabytes
Use reflected light projected by a laser
Lands and Pits represent 1’s and 0’s
Formats
Compact Disk (CD)
Digital Versatile Disk (DVD)
DataPlay
Optical Disks
Slide
35
Widely used format today
Can store from 650 MB to 1 GB
Rotational speed = data transfer time
Types of CDs
CD-ROM
CD-R
CD-RW
Compact Disks
Slide
36
Compact Disc-Read Only Memory
Cannot be written to or erased
Similar to commercial music CDs
Used often to distribute large databases or
references
CD-ROM
Slide
37
CD-Recordable
Written to once
Custom made music CDs
CD-ReWritable
Erasable CD
Ideal for multimedia presentations
CD-R & CD-RW
Slide
38
Digital Versatile Disk
Rapidly replacing CDs
Higher capacity
17 times the capacity of a CD
DVD
Slide
39
DVD types
DVD-ROM
Read only memory
DVD-R
Recordable
DVD-RAM or DVD-RW
Competing rewritable formats
DVD Types
Slide
40
Complement other secondary storage devices
Specialized device types
Magnetic tape
Internet hard drives
Solid state storage
Other Secondary Storage Types
Slide
41
Sequential access
Commonly used for backing-up data
Very large capacity
Types of magnetic tape
Tape cartridges
Magnetic tape reels
Magnetic Tape
Slide
42
Tape cartridges
Backup tape for microcomputer
Capacities range from 120 MB to 5 GB
Digital audio tape (DAT)
Tape reels
Minicomputer and mainframe
1/2 inch wide and 1/2 mile long
Stores 1600 to 6400 cpi
Magnetic Tape Types
Slide
43
Internet hard drive
Free or low-cost storage on the Web
Access information from any location
Access time is greater
Solid-state storage
No moving parts
Flash memory cards
Internet Hard Drive and Solid State
Slide
44
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Memory in computers is essential for storing and processing data. It is composed of semiconductor switches that represent binary numbers as 0s and 1s. This article covers the basics of memory, including bits, ROM, and RAM, explaining their functions and significance in a computer system. It also discusses why ROM and RAM are needed, along with how memory is accessed by the CPU through address and data buses.


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  1. Computer Memory

  2. What is memory? Memory is made up of semi-conductor switches. The position of the switch (open or closed) is used to represent the binary numbers 0 or 1. Slide 2

  3. Bit Basics Bit: From Binary digit Smallest unit of information computer can process Can have one of two values: 0 or 1 A single unit of memory is called a BIT and can store 0 or 1. Two BITS together allow 4 different binary numbers to be stored: 00 , 01 , 10 or 11. Eight BITS can store 256 different numbers: 00000000 through to 11111111 Byte Collection of 8 bits Can represent 256 different messages (256 = 28) Slide 3

  4. What is ROM and RAM? RAM Random Access Memory The contents of RAM can be altered so a computer can both read from and write to memory addresses in RAM. RAM is described as volatile meaning that if the power is switched off or the battery removed then the contents will be lost. ROM - Read only Memory The contents of ROM cannot be altered so a computer can only read from memory addresses in ROM. ROM is described as non-volatile meaning that if the power is switched off or the battery removed then the contents are not lost. Slide 4

  5. Why is ROM needed in a computer? ROM is needed for devices where programs or data must not be lost when the power is turned off or batteries are removed etc. Embedded computers such as those in microprocessor controlled devices use ROM to store the software to control the hardware, as well as data such as cooking/washing times etc. A typical computer uses special ROM called the BIOS (Basic Input/Output System) which permanently stores the software needed to access computer hardware such as the hard drive and then load an operating system into RAM and start to execute it. Slide 5

  6. Why is RAM needed in a computer? When a personal computer is in use the following are copied into RAM from the backing storage: The Operating System (OS) All the other programs that are running Any data files that are in use. RAM is needed for this task because it would be far too slow for the CPU to directly access this data from the secondary storage. New files or changes made to files while the computer system is in use need to be saved before is switched off. This is done by copying the data from RAM to the secondary storage. Slide 6

  7. How is memory accessed Memory is linked to the CPU by two different types of BUS, the address bus and the data bus (a BUS is a set of very thin parallel wires that transmit binary data). The ADDRESS BUS identifies the location of the data (a bit like a house number/postcode does). The DATA BUS is then used to transfer the contents of the memory address (the data) between the memory location and the CPU (and visa-versa with RAM). MEMORY ADDRESS MEMORY CONTENTS 1 0 0 1 1 1 1 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 1 0 0 1 0 1 0 1 1 0 0 0 0 0 1 1 Slide 7

  8. How does the amount of RAM affect performance? When a computer is running, the operating system, all the other running programs plus any files in use are all stored in RAM. This is because secondary storage (such as a hard drive) would be far too slow for the CPU. If there is insufficient RAM then the CPU has to constantly transfer blocks of data between RAM and virtual memory. This will significantly slow the rate that the computer can process instructions and data. SUMMARY: The more RAM installed in a personal computer, the higher the performance. Slide 8

  9. What is virtual memory Because there is only a limited amount of RAM in a computer it is possible for it to run low if too many programs are running at one time OR too many large files have been loaded. However, at any one time only some blocks of the data in RAM are actively being used by the CPU so it is possible for the OS to copy blocks of inactive data from RAM to the hard drive and copy active blocks of data into RAM to be accessed by the CPU. To the CPU, it therefore appears that all the programs are running from RAM and each program behaves as if it had as much RAM as it needed, hence the term virtual memory. This solution is a very cheap but does have its limitations. Because the hard drive is so much slower than RAM, this swapping of inactive and active data blocks will cause a slight delay as the computer switches tasks. If a computer is very low on RAM or accessing many different areas of memory then it will slow down dramatically because too much time will be spent swapping blocks of data between real and virtual memory. The area of the hard disk that acts as the virtual memory is called a page file and the size can set using the Operating System. It is usually set to be around twice the size of the RAM. SUMMARY: Virtual memory is memory that uses secondary storage but to a program it appears as if the whole program is loaded and running from RAM. Slide 9

  10. What is cache memory? Cache memory is a small amount of very fast memory that is built into the CPU. Blocks of instructions and data that are in use by the CPU are copied from RAM into cache memory, along with the associated memory addresses. If the CPU needs to access a memory address it first checks the cache memory to see if there is a match. If there is then it access the contents of the cache version. Summary: A CPU with a larger cache memory and more levels of cache memory will have a higher performance than one without cache memory. Slide 10

  11. What is flash memory? Flash memory is a special type of RAM that, unlike normal RAM, is non- volatile (it does not need a power supply to preserve the memory contents). Flash memory cannot however replace RAM in a computer as the read/write speeds are too slow. Flash memory can be described as a solid state storage device because the contents are non-volatile and there are no moving parts. Typical storage sizes range from 1GB to 16GB and higher. Examples of flash memory in use: Compact Flash and Secure Digital (SD) memory cards in digital cameras. Mini and Micro SD cards in smart phones. Memory cards for video game consoles. USB memory sticks. SUMMARY: Flash memory combines the permanence of ROM with the flexibility of RAM, but not the speed. Slide 11

  12. How are changes in memory technologies leading to innovative computer designs? SUMMARY: Memory technology has developed significantly over the years. Changes include: Greater storage density; (the number of bits per chip has increased from almost 1 kilobit (Kb) to 2 gigabit (GB) per chip) meaning computer systems, in particular portable ones, can be much smaller. Faster read/write times; allowing increases in the performance of computer systems, although these speed increases still lag behind the advances in processor speeds. Less power consumption; allowing mains computers to consume less electricity and portable computing devices to last longer on battery power or use smaller batteries and be even more portable. Lower costs per gigabit; making it affordable to install significant amounts of RAM in quite basic computer systems. Flash memory capacity has risen to the point where solid state storage becomes a realistic alternative to the hard drive in smaller systems. This means that a computer can start operating far more quickly when it is started up as the data can be copied into RAM so much faster. Cache memory built into the CPU has made data transfer between the processor and RAM far more efficient, allowing significant increases in performance at a reasonable cost. Slide 12

  13. Different types of Memory Slide 13

  14. What is Random-access Memory? 1) RAM stands for Random-Acess Memory. It means that the CPU (Central Processing Unit) can directly access any address location of RAM memory. Thus, RAM is a quickly accessible memory of the computer. But it stores the data temporarily. 2) RAM is a volatile memory. It means that it loses the data stored in it when the power is turned off. 3) The programs that the CPU requires during the execution of any program are stored in this memory. 4) It is the fastest and also the costliest memory of a computer. It is a read-write memory of the computer. Thus, the data in RAM can be modified. 5) It is further classified into two types SRAM (Static Random Access Memory) and DRAM (Dynamic Random Access Memory). a) SRAM i.e. the Static RAM requires the constant flow of the power/electricity to retain the data inside it. b) DRAM i.e. the Dynamic RAM needs to be refreshed to retain the data it holds. Slide 14

  15. Comparison between DRAM and SRAM Slide 15

  16. What is ROM? 1) ROM stands for Read-Only Memory. The CPU can not directly access the ROM memory. The data is, first, transferred to RAM and then the CPU can access that data from the RAM. 2) ROM is a non-volatile memory. This means that the data inside it retains even if the power of the CPU is switched off. 3) This memory stores all the crucial information essential to operate the system, like the program to boot the computer. 4) ROM is generally used in Embedded systems such as calculator, peripheral devices, etc. 5) It is further classified into 3 types PROM, EPROM, and EEPROM. Slide 16

  17. Types of Read-Only Memory 1) PROM It stands for Programmable read-only memory. Once the user has programmed it, the data and instructions in it cannot be changed. 2) EPROM Erasable Programmable read-only memory. It means that it can be reprogrammed. In order to erase data from it, we need to expose it to ultraviolet light. After that, the user can reprogram it again, 3) EEPROM Electrically erasable programmable read-only memory. To erase the data we need to apply an electric field, unlike the EPROM where we needed ultraviolet light. But we can only erase only portions of the chip. Slide 17

  18. Differences between RAM and ROM Slide 18

  19. Memory Unit Capacity 1 or 0 (on or off) 8 bits 1024 bytes 1024 kilobytes 1024 megabytes 1024 gigabytes 1024 terabytes 1024 petabytes 1024 exabytes 1024 zettabytes Unit Bit Byte Kilobyte Megabyte Gigabyte Terabyte Petabyte Exabyte Zettabyte Yottabyte Shortened b B KB MB GB TB PB EB ZB YB Slide 19

  20. Picking the Best Data Storage Solution DAS: DAS solutions are typically the simplest and the cheapest. High capacity backup hard drives, solid state drives, and optical disc drives are all examples of DAS solutions. Because of the relatively cheap price and minimal space obstruction, DAS is a great choice for very small businesses with only a handful of employees. Remote access is usually not possible with DAS. Slide 20

  21. Picking the Best Data Storage Solution . Contd. NAS: Small to mid-size companies have more demanding data storage requirements than small businesses. NAS allows these companies to store data in a centralized location, and can be accessed remotely from various devices on your network. NAS are usually pieces of hardware fitted with multiple hard drives in a RAID configuration, and can be connected to a switch or router on a network via a network interface card. If your business is looking for centralized storage, remote access, file sharing, and scalability, consider utilizing a NAS solution. Slide 21

  22. Picking the Best Data Storage Solution .. Contd. SAN: SAN solutions are a good fit for large companies and enterprises that have the space to store multiple disk arrays, switches, and servers. SAN gives access to large blocks of data between servers and storage devices across multiple locations. This solution is a necessity for any large company that needs to reliably and quickly access massive amounts of data. SAN also provides a higher level of data security and is much more fault tolerant than NAS and DAS. Slide 22

  23. SECONDARY STORAGE Secondary storage is also called external, secondary or auxiliary memory. This type of storage holds data for the long term. Data stored on secondary storage devices can only be removed by deleting it. Secondary memory is where the operating system, hardware drivers and data created by the user is kept and stored permanently. This means that, in the case of power failures, secondary storage will preserve the information that is saved to it, even if the power to the computer is lost, while the data on the primary storage devices will be lost. The most common example of secondary storage is the hard drive inside a computer. Other examples include solid-state drives (SSDs), USB flash drives and secure digital (SD) cards. Slide 23

  24. Comparison: Memory versus storage Slide 24

  25. STORAGE MEDIA FOR BACKUP One purpose of storage devices is to back up or archive your important data. In the business world, there is a need to store data permanently and in a way that does not get destroyed, corrupted or damaged easily. Different types of storage media can be used for backing up or archiving. Backups are records of important information that is used often. Backups are kept for a relatively short period of time. Slide 25

  26. Secondary Storage Stores information Non-volatile, permanent storage Characteristics Media Capacity Access time Slide 26

  27. Types of Storage Media Types widely used today Floppy disks Hard disks Optical disks Magnetic tape Slide 27

  28. Floppy Disks Portable and removable Flat circular Mylar media Magnetic charge on metal oxide film coating Standard 2HD 1.44 MB Parts Tracks Sectors Slide 28

  29. High Capacity Floppy Disks Floppy disk cartridges Zip Disks 250 MB SuperDisks 120 MB HiFD disks 200 MB Slide 29

  30. Hard Disks Metallic disks Fast retrieval, greater capacity Read/write heads ride cushion of air .000001 thick Three types Internal hard disk Hard-disk cartridge Hard-disk pack Slide 30

  31. Internal Hard Disk Inside system unit Non-removable or portable Great capacity Upto 2 TB Fast access speed Slide 31

  32. Hard-disk Cartridges Portable, removable Complement internal hard drive Slide 32

  33. Hard-disk Packs Used in mainframes Removable Resemble stack of vinyl records Multiple read/write heads Massive storage capacity Fast access time Slide 33

  34. Performance Enhancements Improving performance of hard disks Disk caching Redundant Arrays of Inexpensive Disks (RAID) File compression and decompression Slide 34

  35. Optical Disks Very large capacity Up to 17 gigabytes Use reflected light projected by a laser Lands and Pits represent 1 s and 0 s Formats Compact Disk (CD) Digital Versatile Disk (DVD) DataPlay Slide 35

  36. Compact Disks Widely used format today Can store from 650 MB to 1 GB Rotational speed = data transfer time Types of CDs CD-ROM CD-R CD-RW Slide 36

  37. CD-ROM Compact Disc-Read Only Memory Cannot be written to or erased Similar to commercial music CDs Used often to distribute large databases or references Slide 37

  38. CD-R & CD-RW CD-Recordable Written to once Custom made music CDs CD-ReWritable Erasable CD Ideal for multimedia presentations Slide 38

  39. DVD Digital Versatile Disk Rapidly replacing CDs Higher capacity 17 times the capacity of a CD Slide 39

  40. DVD Types DVD types DVD-ROM Read only memory DVD-R Recordable DVD-RAM or DVD-RW Competing rewritable formats Slide 40

  41. Other Secondary Storage Types Complement other secondary storage devices Specialized device types Magnetic tape Internet hard drives Solid state storage Slide 41

  42. Magnetic Tape Sequential access Commonly used for backing-up data Very large capacity Types of magnetic tape Tape cartridges Magnetic tape reels Slide 42

  43. Magnetic Tape Types Tape cartridges Backup tape for microcomputer Capacities range from 120 MB to 5 GB Digital audio tape (DAT) Tape reels Minicomputer and mainframe 1/2 inch wide and 1/2 mile long Stores 1600 to 6400 cpi Slide 43

  44. Internet Hard Drive and Solid State Internet hard drive Free or low-cost storage on the Web Access information from any location Access time is greater Solid-state storage No moving parts Flash memory cards Slide 44

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