MEMORY

1
MEMORY STORAGE

• Intro to Computer Technologies

2
OBJECTIVES

• Understand the PCs logical memory layout
• Understand the levels of BYTES
• Explain uses/purposes for removable storage
• Understand the difference between RAM the Hard
  Drive

3
Computer Memory Basics

• Although memory is technically any form of
  electronic storage, it is used most often to
  identify fast, temporary forms of storage.
• If your computer's CPU had to constantly access
  the hard drive to retrieve every piece of data it
  needs, it would operate very slowly. When the
  information is kept in memory, the CPU can access
  it quicker. Most forms of memory are intended to
  store data temporarily.

4
Memory Hierarchy

• The CPU accesses memory according to a distinct
  hierarchy. Whether it comes from permanent
  storage or input, most data goes in random access
  memory (RAM) first.

• The CPU then stores pieces of data it will need
  to access, often in a cache.

5
Memory Hierarchy

• All of the components in your computer work
  together as a team, and memory is one of the most
  essential parts of this team.
• From the moment you turn your computer on until
  the time you shut it down, your CPU is constantly
  using memory.

6
What Happens?

• You turn the computer on.
• The computer loads data from read-only memory
  (ROM) and performs a power-on self-test (POST) to
  make sure all the major components are
  functioning properly.
• The memory controller checks all of the memory
  addresses with a quick read/write operation to
  ensure that there are no errors in the memory
  chips.
• The computer loads the basic
• input/output system (BIOS) from ROM.

7
What Happens?

• The computer loads the operating system (OS) from
  the hard drive into the system's RAM.
• To conserve RAM usage, many applications load
  only the essential parts of the program initially
  and then load other pieces as needed.
• After an application is loaded, any files that
  are opened for use in that application are loaded
  into RAM.
• When you save a file and close the application,
  the file is written to the specified storage
  device, then it is removed from RAM.

8
What Happens?

• Every time something is loaded or opened, it is
  placed into RAM.
• The CPU requests the data it needs from RAM,
  processes it and writes new data back to RAM in a
  continuous cycle.
• When an application is closed it is deleted from
  RAM to make room for new data. If the changed
  files are not saved to a permanent storage device
  before being deleted, they are lost.

9
Why does a computer need so many memory systems?

• Fast, powerful CPUs need quick and easy access to
  large amounts of data in order to maximize their
  performance.
• If the CPU cannot get to the data it needs, it
  literally stops and waits for it. Modern CPUs
  running at speeds of about 1 gigahertz can
  consume massive amounts of data -- potentially
  billions of bytes per second.
• The problem that computer designers face is that
  memory that can keep up with a 1-gigahertz CPU is
  extremely expensive.

10
Reason for Cache

• A computer's system RAM alone is not fast enough
  to match the speed of the CPU. That is why you
  need a cache.
• However, the faster RAM is, the better. Most
  chips today operate with a cycle rate of 50 to 70
  nanoseconds.

11
Double Data Rate

• DDR memory is an evolutionary design in which
  data is transferred twice as quickly.
• DDR memory achieves the doubling in performance
  by transferring twice per transfer cycle once at
  the leading edge and once at the trailing edge of
  the cycle.

12
Single Inline Memory Module

• DRAM chips are grouped together into SIMMs.
• The bus from a SIMM to the actual memory chips is
  32 bits wide.

• Need 2 to work in a 64 bit system
• The processor would then access the two SIMMs
  simultaneously.

13
Dual Inline Memory Module

• DIMMs have a 64-bit data path.
• Were introduced to eliminate inefficiency.
• Have separate electrical contacts on each side of
  the module

14
What is a Hard Disk Drive?

• Primary storage unit on a computer
• Consists of one or more magnetic media platters
• Digital data can be written and erased
  magnetically.
• Stores changing digital information in a
  relatively permanent form.
• Retains information when off
• Size measured in Gigabytes

15
Beginning of the Hard Drive

• Invented in the 1950s.
• Started as large disks up to 20 inches in
  diameter holding just a few megabytes.
• Became known as "hard disks" to distinguish them
  from "floppy disks."
• Have a hard platter that holds the magnetic
  medium
• A hard disk can access any
• of its information in a fraction
• of a second.

16
Capacity Performances

• New desktops hard disk capacity starts at a
  minimum of 80 gigabytes.
• Data is stored onto the disk in the form of
  files.
• A file is simply a named collection of bytes.
• The instructions of a software application
• The records of a data base
• The pixel colors for a GIF image.
• No matter what it contains, a
• file is simply a string of bytes.

17
BYTE THIS

• 8 bits 1 byte (One Letter)
• 1024 B 1 Kilobyte (One Sentence)
• 1024 kB 1 Megabyte (A Novel)
• 1024 MB 1 Gigabyte (33 of books)
• 1024 GB 1 Terabyte (50,000 trees/paper)
• 1024 TB 1 Petabyte (?????????????)

18
How Much Space?

• 1 Page Reaction Paper
• Digital Photograph
• 4 Minute Song
• Game
• A 2-Hour DVD

• 30-40 kB
• 2.7 MB
• 4 MB
• 480 MB
• 2.3 GB

19
External Hard Drives

• Connect through either a USB 2.0 or a FireWire
  connection
• Buy it, connect it, turn computer on.
• Comes with configuration instructions, Likely be
  plug-and-play
• Files can be saved immediately
• Plug into multiple machines and
• move files around
• Portable.
• Slower than an internal drive.

20
Removable Storage Uses

• Commercial software
• Making back-up copies of important information
• Transporting data between two computers
• Storing software and information that you don't
  need to access constantly
• Copying information to give to someone else
• Securing information that you don't want anyone
  else to access

21
Removable Storage Devices

• Floppy Disks 5.5, 3.5 1.44 MB
• ZIP 750 MB
• Cartridges 2 GB
• CD 700 MB
• DVD 4 GB
• Memory Cards 4 GB
• Flash Memory 16 GB

22
Differences

• MEMORY
• FAST
• TEMPORARY
• EXPENSIVE
• VOLATILE
• A memory device that does not retain stored
  information when power is interrupted

• STORAGE
• SLOW
• PERMANENT
• CHEAP
• NON-VOLATILE