Chapter 9: System Memory Internal Memory - PowerPoint PPT Presentation

Loading...

PPT – Chapter 9: System Memory Internal Memory PowerPoint presentation | free to download - id: 6e7065-YmE2M



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Chapter 9: System Memory Internal Memory

Description:

Chapter 9: System Memory Internal Memory Dr Mohamed Menacer Taibah University 2007-2008 – PowerPoint PPT presentation

Number of Views:16
Avg rating:3.0/5.0
Date added: 13 February 2020
Slides: 50
Provided by: mme136
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Chapter 9: System Memory Internal Memory


1
Chapter 9 System Memory Internal Memory
Dr Mohamed Menacer Taibah University 2007-2008
2
Semiconductor Memory Types
3
Semiconductor Memory
  • RAM
  • Misnamed as all semiconductor memory is random
    access
  • Read/Write
  • Volatile
  • Temporary storage
  • Static or dynamic

4
Memory Cell Operation
5
Dynamic RAM
  • Bits stored as charge in capacitors
  • Charges leak
  • Need refreshing even when powered
  • Simpler construction
  • Smaller per bit
  • Less expensive
  • Need refresh circuits
  • Main memory
  • Essentially analogue
  • Level of charge determines value

6
Dynamic RAM Structure
7
DRAM Operation
  • Address line active when bit read or written
  • Transistor switch closed (current flows)
  • Write
  • Voltage to bit line
  • High for 1 low for 0
  • Then signal address line
  • Transfers charge to capacitor
  • Read
  • Address line selected
  • transistor turns on
  • Charge from capacitor fed via bit line to sense
    amplifier
  • Compares with reference value to determine 0 or 1
  • Capacitor charge must be restored

8
Static RAM
  • Bits stored as on/off switches
  • No charges to leak
  • No refreshing needed when powered
  • More complex construction
  • Larger per bit
  • More expensive
  • Does not need refresh circuits
  • Faster
  • Cache
  • Digital (Uses flip-flops)

9
Stating RAM Structure
10
Static RAM Operation
  • Transistor arrangement gives stable logic state
  • State 1
  • C1 high, C2 low
  • T1 T4 off, T2 T3 on
  • State 0
  • C2 high, C1 low
  • T2 T3 off, T1 T4 on
  • Address line transistors T5 T6 is switch
  • Write apply value to B compliment to B
  • Read value is on line B

11
SRAM v DRAM
  • Both volatile
  • Power needed to preserve data
  • Dynamic cell
  • Simpler to build, smaller
  • More dense
  • Less expensive
  • Needs refresh
  • Larger memory units
  • Static
  • Faster
  • Cache

12
Read Only Memory (ROM)
  • Permanent storage
  • Nonvolatile
  • Microprogramming (see later)
  • Library subroutines
  • Systems programs (BIOS)
  • Function tables

13
Types of ROM
  • Written during manufacture
  • Very expensive
  • Programmable (once)
  • PROM
  • Needs special equipment to program
  • Read mostly
  • Erasable Programmable (EPROM)
  • Erased by UV
  • Electrically Erasable (EEPROM)
  • Takes much longer to write than read
  • Flash memory
  • Erase whole memory electrically

14
Organisation in detail
  • A 16Mbit chip can be organised as 1M of 16 bit
    words
  • A bit per chip system has 16 lots of 1Mbit chip
    with bit 1 of each word in chip 1 and so on
  • A 16Mbit chip can be organised as a 2048 x 2048 x
    4bit array
  • Reduces number of address pins
  • Multiplex row address and column address
  • 11 pins to address (2112048)
  • Adding one more pin doubles range of values so x4
    capacity

15
Refreshing
  • Refresh circuit included on chip
  • Disable chip
  • Count through rows
  • Read Write back
  • Slows down apparent performance

16
Typical 16 Mb DRAM (4M x 4)
17
Packaging
18
Advanced DRAM Organization
  • Basic DRAM same since first RAM chips
  • Enhanced DRAM
  • Contains small SRAM as well
  • SRAM holds last line read (c.f. Cache!)
  • Cache DRAM
  • Larger SRAM component
  • Use as cache or serial buffer

19
Synchronous DRAM (SDRAM)
  • Access is synchronized with an external clock
  • Address is presented to RAM
  • RAM finds data (CPU waits in conventional DRAM)
  • Since SDRAM moves data in time with system clock,
    CPU knows when data will be ready
  • CPU does not have to wait, it can do something
    else
  • Burst mode allows SDRAM to set up stream of data
    and fire it out in block
  • DDR-SDRAM sends data twice per clock cycle
    (leading trailing edge)

20
SDRAM
  • CLK Clock input RAS Raw
    Address Strobe CKE Clock Enable
    CAS Column Address Strobe CS Chip Select
    A0-A13 Address Input WE
    Write Enable DQ0-DQ7 Data
    Input/Output

21
DDR SDRAM
  • SDRAM can only send data once per clock
  • Double-data-rate SDRAM can send data twice per
    clock cycle
  • Rising edge and falling edge

22
Cache DRAM
  • Integrates small SRAM cache (16 kb) onto generic
    DRAM chip
  • Used as true cache
  • 64-bit lines
  • Effective for ordinary random access
  • To support serial access of block of data
  • E.g. refresh bit-mapped screen
  • CDRAM can prefetch data from DRAM into SRAM
    buffer
  • Subsequent accesses solely to SRAM

23
External Memory
24
Types of External Memory
  • Magnetic Disk
  • Hard Disk
  • 1.44 Mbyte Floppy Disk
  • RAID (Redundant Array of Independent Disks
  • Removable
  • Optical Disk
  • CD-ROM, CD-Recordable (CD-R)
  • CD-R/W
  • DVD, DVD-R/W
  • Magnetic Tape

25
Magnetic Disk (Hard Disk, Floppy, Raid)
  • Disk substrate coated with magnetizable material
    (iron oxiderust)
  • Substrate used to be aluminium
  • Now glass
  • Improved surface uniformity
  • Increases reliability
  • Reduction in surface defects
  • Reduced read/write errors
  • Lower flight heights (See later)
  • Better shock/damage resistance

26
Read and Write Mechanisms
  • Recording retrieval via conductive coil called
    a head
  • May be single read/write head or separate ones
  • During read/write, head is stationary, platter
    rotates
  • Write
  • Current through coil produces magnetic field
  • Pulses sent to head
  • Magnetic pattern recorded on surface below
  • Read (traditional)
  • Magnetic field moving relative to coil produces
    current
  • Coil is the same for read and write
  • Read (contemporary)
  • Separate read head, close to write head
  • Partially shielded magneto resistive (MR) sensor
  • High frequency operation
  • Higher storage density and speed

27
Inductive Write MR Read
28
Data Organization and Formatting
  • Concentric rings or tracks
  • Gaps between tracks
  • Reduce gap to increase capacity
  • Same number of bits per track (variable packing
    density)
  • Constant angular velocity
  • Tracks divided into sectors
  • Minimum block size is one sector
  • May have more than one sector per block

29
Disk Data Layout
30
Disk Layout Methods Diagram
31
Winchester Disk Format Seagate ST506
32
Characteristics
  • Fixed (rare) or movable head
  • Removable or fixed
  • Single or double (usually) sided
  • Single or multiple platter
  • Head mechanism
  • Contact (Floppy)
  • Fixed gap
  • Flying (Winchester)

33
Multiple Platters
34
Timing of Disk I/O Transfer
  • Seek time
  • Moving head to correct track
  • (Rotational) latency
  • Waiting for data to rotate under head
  • Access time Seek Latency
  • Transfer rate

35
Floppy Disk
  • 8, 5.25, 3.5
  • Small capacity
  • Up to 1.44Mbyte (2.88M never popular)
  • Slow
  • Universal
  • Cheap
  • Obsolete?

36
Winchester Hard Disk
  • Universal
  • Cheap
  • Fastest external storage
  • Getting larger all the time
  • 250 Gigabyte now easily available

37
RAID
  • Redundant Array of Independent Disks
  • Redundant Array of Inexpensive Disks
  • 6 levels in common use
  • Not a hierarchy
  • Set of physical disks viewed as single logical
    drive by O/S
  • Data distributed across physical drives
  • Can use redundant capacity to store parity
    information

38
Optical Disk Storage CD-ROM
  • Originally for audio
  • 650Mbytes giving over 70 minutes audio
  • Polycarbonate coated with highly reflective coat,
    usually aluminium
  • Data stored as pits
  • Read by reflecting laser
  • Constant packing density
  • Constant linear velocity

39
CD Operation
40
CD-ROM Drive Speeds
  • Audio is single speed
  • Constant linier velocity
  • 1.2 ms-1
  • Track (spiral) is 5.27km long
  • Gives 4391 seconds 73.2 minutes
  • Other speeds are quoted as multiples
  • e.g. 24x
  • Quoted figure is maximum drive can achieve

41
CD-ROM Format
  • Mode 0blank data field
  • Mode 12048 byte dataerror correction
  • Mode 22336 byte data

42
Random Access on CD-ROM
  • Difficult
  • Move head to rough position
  • Set correct speed
  • Read address
  • Adjust to required location

43
CD-ROM for against
  • Large capacity (?)
  • Easy to mass produce
  • Removable
  • Robust
  • Expensive for small runs
  • Slow
  • Read only

44
Other Optical Storage
  • CD-Recordable (CD-R)
  • WORM
  • Now affordable
  • Compatible with CD-ROM drives
  • CD-RW
  • Erasable
  • Getting cheaper
  • Mostly CD-ROM drive compatible
  • Phase change
  • Material has two different reflectivities in
    different phase states

45
DVD - whats in a name?
  • Digital Video Disk
  • Used to indicate a player for movies
  • Only plays video disks
  • Digital Versatile Disk
  • Used to indicate a computer drive
  • Will read computer disks and play video disks
  • Officially - nothing!!!

46
DVD - technology
  • Multi-layer
  • Very high capacity (4.7G per layer)
  • Full length movie on single disk
  • Using MPEG compression
  • Finally standardized
  • Movies carry regional coding
  • Players only play correct region films
  • Can be fixed

47
DVD Writable
  • Loads of trouble with standards
  • First generation DVD drives may not read first
    generation DVD-W disks
  • First generation DVD drives may not read CD-RW
    disks
  • Wait for it to settle down before buying!

48
CD and DVD
49
Magnetic Tape
  • Serial access
  • Slow
  • Very cheap
  • Backup and archive
About PowerShow.com