Computer Structure
PC Structure and Peripherals
Lihu Rappoport and Adi Yoaz
1
Computer Structure 2013 – PC Structure and Peripherals
Hard Disks
2
Computer Structure 2013 – PC Structure and Peripherals
Hard Disk Structure


Rotating platters coated with a magnetic surface
 Each platter is divided to tracks: concentric circles
 Each track is divided to sectors
• Smallest unit that can be read or written
 Disk outer tracks have more space for
sectors than the inner tracks
• Constant bit density: record more
sectors on the outer tracks
• speed varies with track location
Sector
Track
Moveable read/write head
 Radial movement to access all tracks
 Platter rotation to access all sectors
Platters

Buffer Cache
 A temporary data storage area
used to enhance drive performance
3
Computer Structure 2013 – PC Structure and Peripherals
Hard Disk Structure
4
Computer Structure 2013 – PC Structure and Peripherals
Disk Access




Seek: position the head over the proper track
 Average: Sum of the time for all possible seek / total # of possible seeks
 Due to locality of disk reference, actual average seek is shorter: 4 to 12 ms
Rotational latency: wait for desired sector to rotate under head
 The faster the drives spins, the shorter the rotational latency time
 Most disks rotate at 5,400 to 15,000 RPM
• At 7200 RPM: 8 ms per revolution
 An average latency to the desired information is halfway around the disk
• At 7200 RPM: 4 ms
Transfer block: read/write the data
 Transfer time is a function of: sector size, rotation speed,
and recording density: bits per inch on a track
 Typical values: 100 MB / sec
Disk Access Time = Seek time + Rotational Latency + Transfer time
+ Controller Time + Queuing Delay
5
Computer Structure 2013 – PC Structure and Peripherals
EIDE Disk Interface

EIDE, PATA, UltraATA, ATA 100, ATAPI: all the same interface





Uses for connecting hard disk drives and CD/DVD drives
80-pin cable, 40-pin dual header connector
100 MB/s
EIDE controller integrated with the motherboard
EIDE controller has two channels





6
Primary and a secondary, which work independently
Two devices per channel: master and slave, but equal
• The 2 devices take turns in controlling the bus
If there are two device on the system (e.g., a hard disk and a CD/DVD)
• It is better to put them on different channels
Avoid mixing slower (DVD) and faster devices (HDD) on the same channel
If doing a lot of copying from drive to drive
• Better performance by separating devices to separate channels
Computer Structure 2013 – PC Structure and Peripherals
Disk Interface – Serial ATA (SATA)

Point-to-point connection







Easier routing, easier installation, better reliability, improved airflow
1/6 the board area compared to EIDE connector
4 wires for signaling + 3 ground to minimize impedance and crosstalk
Current HDDs still do not utilize SATA rev 3 BW


7
SATA rev 1: 150 MB/sec
SATA rev 2: 300 MB/sec
SATA rev 3: 600 MB/sec
Thinner (7 wires), flexible, longer cables


No master/slave jumper configuration needed
when a adding a 2nd SATA drive
Increased BW


Dedicated BW per device (no sharing)
HDD peak (not sustained) gets to 157 MB/s
SSD gets to 250 MB/sec
Computer Structure 2013 – PC Structure and Peripherals
Flash Memory

Flash is a non-volatile, rewritable memory

NOR Flash

Supports per-byte data read and write (random access)
• Erasing (setting all the bits) done only at block granularity (64-128KB)
• Writing (clearing a bit) can be done at byte granularity


Suitable for storing code (e.g. BIOS, cell phone firmware)
NAND Flash

Supports page-mode read and write (0.5KB – 4KB per page)
• Erasing (setting all the bits) done only at block granularity (64-128KB)

Suitable for storing large data (e.g. pictures, songs)
• Similar to other secondary data storage devices
8

Reduced erase and write times

Greater storage density and lower cost per bit
Computer Structure 2013 – PC Structure and Peripherals
Flash Memory Principles of Operation
Information is stored in an array of memory cells
 In single-level cell (SLC) devices, each cell stores one bit
 Multi-level cell (MLC) devices store multiple bits per cell using multiple levels of
electrical charge

Each memory cell is made from a floating-gate transistor
 Resembles a standard MOSFET, with two gates instead of one
• A control gate (CG), as in other MOS transistors, placed on top
• A floating gate (FG), interposed between the CG and the MOSFET channel
 The FG is insulated all around by an oxide layer  electrons placed on it are trapped
• Under normal conditions, will not discharge for many years
 When the FG holds a charge, it partially cancels the electric field from the CG
• Modifies the cell’s threshold voltage (VT): more voltage has to be applied to the
CG to make the channel conduct
 Read-out: apply a voltage intermediate between the
possible threshold voltages to the CG
• Test the channel's conductivity by sensing
the current flow through the channel
• In a MLC device, sense the amount of current flow

9
Computer Structure 2013 – PC Structure and Peripherals
Flash Write Endurance


Typical number of write cycles
SLC
MLC
NAND flash
100K
1K – 3K
NOR flash
100K to 1M
100K
Bad block management (BBM)

Performed by the device driver software, or by a HW controller
• E.g., SD cards include a HW controller perform BBM and wear leveling

Map logical block to physical block
• Mapping tables stored in dedicated flash blocks or
• Each block checked at power-up to create a bad block map in RAM



ECC compensates for bits that spontaneously fail


10
Each write is verified, and block is remapped in case of write failure
Memory capacity gradually shrinks as more blocks are marked as bad
22 (24) bits of ECC code correct a one bit error in 2048 (4096) data bits
If ECC cannot correct the error during read, it may still detect the error
Computer Structure 2013 – PC Structure and Peripherals
Flash Write Endurance (cont)

Wear-leveling algorithms




Dynamic wear leveling



Map Logical Block Addresses (LBAs) to physical Flash memory addresses
Each time a block of data is written, it is written to a new location
• Link the new block
• Mark original physical block as invalid data
• Blocks that never get written remain in the same location
Static wear leveling


11
Evenly distribute data across flash memory and move data around
Prevent from one portion to wear out faster than another
SSD's controller keeps a record of where data is set down on the drive as
it is relocated from one portion to another
Periodically move blocks which are not written
Allow these low usage cells be used by other data
Computer Structure 2013 – PC Structure and Peripherals
Solid State Drive – SSD
Most manufacturers use "burst rate" for Performance numbers
 Not its steady state or average read rate

Any write operation requires an erase followed by the write


When SSD is new, NAND flash memory is pre-erased
Consumer-grade multi-level cell (MLC)
 Allows ≥2 bit per flash memory cell
 Sustains 2,000 to 10,000 write cycles
 Notably less expensive than SLC drives

Enterprise-class single-level cell (SLC)
 Allows 1 bit per flash memory cell
 Lasts 10× write cycles of an MLC

The more write/erase cycle  the shorter the drive's lifespan
 Use wear-leveling algorithms to evenly distribute writes
 DRAM cache to buffer data writes to reduce number of write/erase cycles
 Extra memory cells to be used when blocks of flash memory wear out

12
Computer Structure 2013 – PC Structure and Peripherals
SSD (cont.)

Data in NAND flash memory organized in fixed size in blocks




13
When any portion of the data on the drive is changed
• Mark block for deletion in preparation for the new data
• Read current data on the block
• Redistribute the old data
• Lay down the new data in the old block
Old data is rewritten back
Typical write amplification is 15 to 20
• For every 1MB of data written to the drive, 15MB to 20MBs of space
is actually needed
• Using write combining reduces write amplification to ~10%
Flash drives compared to HD drives:

Smaller size, faster, lighter, noiseless, lower power

Withstanding shocks up to 2000 Gs (like 10 foot drop onto concrete)

More expensive (cost/byte): ~2$/1GB vs ~0.1$/1GB in HDD
Computer Structure 2013 – PC Structure and Peripherals
The Motherboard
14
Computer Structure 2013 – PC Structure and Peripherals
Computer System Structure – 2009
External
Graphics
Card
HDMI
PCI express ×16
CPU
BUS
LLC
Core
Core
North Bridge (GMCH)
On-board
Graphics
Memory
controller
DDRII
Channel 1
Mem BUS
DDRII
Channel 2
South Bridge (ICH)
PCI express ×1
15
Serial Port
Parallel Port
IO Controller
Floppy
Drive
keybrd
USB
IDE
SATA
controller controller controller
mouse
Old DVD
Drive
Hard
Disk
PCI
Sound
Card
speakers
Lan
Adap
LAN
Computer Structure 2013 – PC Structure and Peripherals
Computer System – Nehalem
External
Graphics
Card
PCI express ×16
DDRIII
Cache
Channel 1
Mem
BUS
DDRIII
Memory
controller
Core
CPU
BUS
Core
Channel 2
North Bridge
On-board
Graphics
HDMI
South Bridge
PCI express ×1
16
Serial Port
Parallel Port
IO Controller
Floppy
Drive
keybrd
USB
SATA
SATA
controller controller controller
mouse
DVD
Drive
Hard
Disk
PCI
Sound
Card
speakers
Lan
Adap
LAN
Computer Structure 2013 – PC Structure and Peripherals
Computer System – Sandy Bridge
External
Graphics
Card
PCI express ×16
2133-1066
MHz
DDRIII
Channel 1
DDRIII
Cache
Mem
BUS
Memory
controller
GFX
System
Agent
Core
Channel 2
Line out
Line in
S/PDIF out
S/PDIF in
Core
Display link
Audio
Codec
4×DMI
South Bridge (PCH)
Display port
HDMI
DVI
D-sub
BIOS
17
Serial Port
Parallel Port
Super I/O
PCI express ×1
LPC
USB
Floppy
Drive
PS/2
keybrd/
mouse
exp
slots
mouse
SATA
DVD
Drive
SATA
Hard
Disk
Lan
Adap
LAN
Computer Structure 2013 – PC Structure and Peripherals
PCH Connections

LPC (Low Pin Count) Bus


Supports legacy, low BW I/O devices
Typically integrated in a Super I/O chip
• Serial and parallel ports, keyboard, mouse, floppy disk controller


Other: Trusted Platform Module (TPM), Boot ROM
Direct Media Interface (DMI)

The link between an Intel north bridge and an Intel south bridge
• Replaces the Hub Interface

DMI shares many characteristics with PCI-E
• Using multiple lanes and differential signaling to form a point-to-point link

Most implementations use a ×4 link, providing 10Gb/s in each direction
• DMI 2.0 (introduced in 2011) doubles the BW to 20Gb/s with a ×4 link

Flexible Display Interface (FDI)

Connects the Intel HD Graphics integrated GPU with the PCH south bridge
• where display connectors are attached

18
Supports 2 independent 4-bit fixed frequency links/channels/pipes at
2.7GT/s data rate
Computer Structure 2013 – PC Structure and Peripherals
Motherboard Layout – 1st Gen Core2TM
IEEE1394a
header
audio
header
PCI express
PCI add-in PCI
express
x1
x16
card
connector connector connector
Back panel
connectors
Processor core power connector
Rear chassis fan header
High Def. Audio header
PCI add-in card connector
LGA775 processor socket
Parallel ATA IDE connector
GMCH: North Bridge + integ GFX
Processor fan header
Speaker
Front panel USB header
4 × SATA
connectors
19
DIMM Channel A sockets
Serial port header
DIMM Channel B sockets
Diskette drive connector
ICH: South Battery
Bridge +
integ Audio
Main
Power
connector
Computer Structure 2013 – PC Structure and Peripherals
Motherboard Layout (Sandy Bridge)
IEEE1394a
header
PCI add-in PCI
express x1
card
connector connector
PCI express
x16
connector
Back panel
connectors
audio
header
Processor core power connector
High Def. Audio header
S/PDIF
Rear chassis fan header
LGA775 processor socket
Processor fan header
DIMM Channel A sockets
DIMM Channel B sockets
Front chassis fan header
Chassis intrusion header
Front panel USB headers
Bios setup config jumper
SATA speaker
connectorsBattery Main
Power
PCH
connector
20
Serial port header
Rear chassis fan header
Computer Structure 2013 – PC Structure and Peripherals
ASUS Sabertooth P67 B3 Sandy Bridge Motherboard
21
Computer Structure 2013 – PC Structure and Peripherals
Motherboard Back Panel
Rear
Surround
USB
2.0
ports
eSATA
22
LAN
port
USB
2.0
ports
USB
2.0
ports
DVI-I
DisplayPort
HDMI
IEEE
1394A
USB
3.0
ports
Center /
subwoofer
Line
in
S/PDIF Mic in
/ Side
surround
Line
out/
Front
speakers
Computer Structure 2013 – PC Structure and Peripherals
System Start-up
Upon computer turn-on several events occur:
1. The CPU "wakes up" and sends a message to activate the BIOS
2. BIOS runs the Power On Self Test (POST):
make sure system devices are working ok







23
Initialize system hardware and chipset registers
Initialize power management
Test RAM
Enable the keyboard
Test serial and parallel ports
Initialize floppy disk drives and hard disk drive controllers
Displays system summary information
Computer Structure 2013 – PC Structure and Peripherals
System Start-up (cont.)
3. During POST, the BIOS compares the system configuration data
obtained from POST with the system information stored on a
memory chip located on the MB


A CMOS chip, which is updated whenever new system components
are added
Contains the latest information about system components
4. After the POST tasks are completed


the BIOS looks for the boot program responsible for loading the
operating system
Usually, the BIOS looks on the floppy disk drive A: followed by drive
C:
5. After boot program is loaded into memory

It loads the system configuration information contained in the
registry in a Windows® environment, and device drivers
6. Finally, the operating system is loaded
24
Computer Structure 2013 – PC Structure and Peripherals
Backup
25
Computer Structure 2013 – PC Structure and Peripherals
Western Digital HDDs
Caviar Green 2TB
Caviar Blue 1TB
Maximum external transfer
rate
Maximum sustained data rate
300MB/s
126MB/s
Average rotational latency
Spindle speed
Cache size
Caviar Black 2TB
138MB/s
4.2 ms
7,200 RPM
7,200 RPM
32MB
64MB
Platter size
500GB
Areal density
400 Gb/in²
Available capacities
2TB
Idle power
6.1W
8.2W
Read/write power
6.8W
10.7W
Idle acoustics
28 dBA
29 dBA
Seek acoustics
33dBA
30-34 dBA
26
Computer Structure 2013 – PC Structure and Peripherals
HDD Example
Performance Specifications
Rotational Speed
Buffer Size
Average Latency
Load/unload Cycles
7,200 RPM (nominal)
64 MB
4.20 ms (nominal)
300,000 minimum
Buffer To Host (Serial ATA)
6 Gb/s (Max)
Formatted Capacity
Capacity
Interface
User Sectors Per Drive
2,000,398 MB
2 TB
SATA 6 Gb/s
3,907,029,168
Transfer Rates
Physical Specifications
Acoustics
Idle Mode
Seek Mode 0
Seek Mode 3
Current Requirements
Power Dissipation
Read/Write
Idle
Standby
Sleep
27
29 dBA (average)
34 dBA (average)
30 dBA (average)
10.70 Watts
8.20 Watts
1.30 Watts
1.30 Watts
Computer Structure 2013 – PC Structure and Peripherals
DDR Comparison
DDR
Bus clock
SDRAM
(MHz)
Standard
28
Internal
rate
(MHz)
Prefetch
(min
burst)
Transfer
Rate
(MT/s)
Voltage
DIMM
pins
DDR
100–200
100–200
2n
200–400
2.5
184
DDR2
200–533
100–266
4n
400–1066
1.8
240
DDR3
400–1066
100–266
8n
800–2133
1.5
240
Computer Structure 2013 – PC Structure and Peripherals
SSD vs HDD
Attribute or characteristic
Random access time[57]
Consistent read
performance[61]
Solid-state drive
Hard disk drive
~0.1 ms
5–10 ms
Read performance does not change based on where data is If data is written in a fragmented way, reading back the
stored on an SSD
data will have varying response times
Fragmentation
Non-issue due
Acoustic levels
Mechanical reliability
SSDs have no moving parts and make no sound
No moving part
Files may fragment; periodical defragmentation is required
to maintain ultimate performance.
Maintenance of temperature Less heat
Susceptibility
to environmental factors
Magneticsusceptibility
Weight and size
Parallel operation
Write longevity
Cost per capacity
Storage capacity
Read/write performance
symmetry
Free block availability
and TRIM
Power consumption
29
No flying heads or rotating platters to fail as a result
of shock, altitude, or vibration
No impact on flash memory
Magnets or magnetic surges can alter data on the media
very light compared to HDDs
Some flash controllers can have multiple flash chips reading HDDs have multiple heads (one per platter) but they are
and writing different data simultaneously
connected, and share one positioning motor.
Flash-based SSDs have a limited number of writes (1-5
Magnetic media do not have a similar limited number of
million or more) over the life of the drive.
writes but are susceptible to eventual mechanical failure.
$.90–2.00 per GB
$0.05/GB for 3.5 in and $0.10/GB for 2.5 in drives
Typically 4-256GB
typically up to 1 – 2 TB
Less expensive SSDs typically have write speeds
HDDs generally have slightly lower write speeds than their
significantly lower than their read speeds. Higher
read speeds.
performing SSDs have a balanced read and write speed.
SSD write performance is significantly impacted by the
availability of free, programmable blocks. Previously written
HDDs are not affected by free blocks or the operation (or
data blocks that are no longer in use can be reclaimed by
lack) of the TRIM command
TRIM; however, even with TRIM, fewer free, programmable
blocks translates into reduced performance.[29][75][76]
High performance flash-based SSDs generally require 1/2 to High performance HDDs require 12-18 watts; drives
1/3 the power of HDDs
designed for notebook computers are typically 2 watts.
Computer Structure 2013 – PC Structure and Peripherals
PC Connections
Raw bandwidth
(Mbit/s)
Transfer speed
(MB/s)
Max. cable
length (m)
3,000
300
2 with eSATA HBA (1
with passive adapter)
5 V/12 V[33]
SATA revision 3.0
SATA revision 2.0
SATA revision 1.0
PATA 133
SAS 600
SAS 300
SAS 150
6,000
3,000
1,500
1,064
6,000
3,000
1,500
600[34]
300
150[35]
133.5
600
300
150
1
No
IEEE 13943200
3,144
393
IEEE 1394800
IEEE 1394400
USB 3.0*
USB 2.0
USB 1.0
SCSI Ultra-640
SCSI Ultra-320
Fibre Channel
over optic fibre
Fibre Channel
over copper cable
786
393
5,000
480
12
5,120
2,560
98.25
49.13
400[38]
60
1.5
640
320
10,520
1,000
Name
eSATA
eSATAp
Power provided
No
1 (15 with port
multiplier)
1 per line
2
0.46 (18 in)
No
10
No
1 (>65k with
expanders)
15 W, 12–25 V
63 (with hub)
4.5 W, 5 V
2.5 W, 5 V
Yes
127 (with hub)[39]
No
15 (plus the HBA)
No
126
(16,777,216 with
switches)
100 (more with
special cables)
100[36]
4.5[36][37]
3[39]
5[40]
3
12
2–50,000
4,000
400
12
InfiniBand
Quad Rate
10,000
1,000
5 (copper)[41][42]<10,0
00 (fiber)
No
Thunderbolt
10,000
1,250
100
10 W
30
Devices per
channel
1 with point to point
Many withswitched
fabric
7
Computer Structure 2013 – PC Structure and Peripherals
USB
USB 2
USB 3
Speed:
480 Mbps
4.8 Gbps
Released:
April 2000
November 2008
Signaling Method:
Polling: either send or receive data
(Half duplex)
Asynchronous: send and receive
data simultaneously (Full duplex)
Up to 500 mA
Up to 900 mA. Allows better power
efficiency with less power for idle
states. Can power more devices
from one hub.
4
9
Grey in color
Blue in color
Power Usage:
Number of wires
within the cable:
StandardAConnectors:
31
Computer Structure 2013 – PC Structure and Peripherals