Advanced Computer Architecture - Lecture 38: Input/Output systems

CS 704
Advanced Computer Architecture

Lecture 38
Input Output Systems
(Storage and I/O Systems)

Prof. Dr. M. Ashraf Chughtai


Today’s Topics
Recap:
Disk Storage Systems
Interfacing Storage Devices

Conclusion

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Recap: Multiprocessing
In last four lectures we discussed how the
computer performance can be improved by
Parallel Architectures
Parallel Architecture is a collection of
processing elements that cooperate and

communicate to solve larger problems fast
Parallel architectures are implemented as:
SIMD, MISD and MIMD machines, where the
MIMD machines facilitate complete parallel
processing
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Recap: Multiprocessing
The MIMD machines are classified as:
– Centralized Shared Memory Architecture
– Distributed Memory Architecture

The centralized memory architecture,
maintain a single centralized memory with
uniform access time
In contrast, the distributed Shared-Memory
multiprocessors have non uniform
memory architecture but offer greater
scalability

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Recap: Multiprocessing
The sharing of caches for multi-processing
introduces cache coherence problem
In Centralized shared-memory architecture, the
cache coherence problem is resolved by using
write invalidation and write broadcasting
schemes those implement Snooping algorithm
In Distributed shared-memory architecture, the
cache coherence problem is resolved by using
Directory Based Protocols
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Recap: outside processor
Today the :
 Processing Power doubles every 18 months
 Memory Size doubles every 18 months; and
 Disk positioning rate (Seek + Rotate) doubles
every 10 Years
Recall the 2nd lecture, where we discussed the
quantitative principles to define the computer

performance, we noticed that the execution
time of CPU is not the only measure of
computer performance
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Introduction: outside the processor
The overall performance of a computer is
measured by its throughput, which is very
much influenced by the systems external to the
processor
As we have already pointed out in 25th lecture
that measuring the overall performance of a
powerful Uni-processor or a parallel processing
architecture without considering the I/O
devices and their interconnection, is just like
trying to determine the road performance of a
car, which is fitted with powerful engine but is
without wheels
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Introduction: outside the processor
The effect of neglecting the I/Os on the overall
performance of a computer system can best be
visualized by Amdahl's Law which identifies
that: system speed-up limited by the slowest
part!
Let us consider computer whose response time
is 10% longer than the CPU time
If the CPU time is speeded up by a factor of 10
then neglecting the I/Os, the overall speed up
as determined using the Amdahl's Law is 5; i.e.,
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Introduction: outside the processor
Half of what we would have achieved if both the
CPU time and I/O time were sped up 10 times
In other words we can say 50% lose in the speedup
Similarly, if the CPU time is speeded up 100 times
and neglecting the I/Os, the overall speed up is 10;
i.e.,
10% of what we would have achieved if both the
CPU time and I/O time were sped up 100 times

In other words we can say that ignoring the I/Os
there is 90% lose in the speed-up
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Introduction: outside the processor
Thus, I/O performance increasingly limits the
system performance and efficiency
After having detailed discussion on the
performance enhancement of:
–
–
–
–
–

instruction Set Architecture
computer hardware
instruction level parallelism
memory hierarchy systems and
parallel processing architecture

We are, now, going to focus our discussion on
the study of the systems outside processor,
i.e., I/O systems

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I/O System
An I/O system comprises storage I/Os and
Communication I/Os
Processor

interrupts

Cache

Memory - I/O Bus
Main
Memory

I/O
Controller
Disk

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Disk

I/O
Controller

I/O
Controller

Graphics

Network

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I/O Systems
The Storage I/Os consist of Secondary and
Tertiary Storage Devices; and
The communication I/O consists of I/O Bus system
which interconnect the microprocessor and
memory with the I/O devices
Today we will talk about the storage I/O
The secondary and tertiary storages include:
magnetic disk, magnetic tape automated tape
libraries, CDs, and DVDs
These devices offer bulk data storage, but on the
contrary are too large for embedded applications
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Disk Storages: Technology Trends
As you can see from the plot shown here that
extensive improvement have been made in the
disk capacity;
before 1990 disk capacity doubled every 36
months; and now every 18 months;

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Storage Technology Drivers
This improvement in the technology trend is
driven by the prevailing computing paradigm
– In 1950s computing observed migration from
batch to on-line processing where as
– In 1990s on-line processing migrated to
ubiquitous computing; i.e.,
computers in phones, books, cars, video
cameras, …
nationwide fiber optical network with

wireless tails
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Storage Technology Drivers
This development in processing effected the
storage industry and motivated to develop:
– the smaller, cheaper, more reliable and lower
power embedded storages for ubiquitous
computing
– high capacity, hierarchically managed
storages as data utilities
Before discussing the storage technologies,
let us perceive the historical perspective of
magnetic storages
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Historical Perspective
1956 - early 1970s

– IBM Ramac and Winchester were developed for
mainframe computers as proprietary interfaces
– Steady shrink in form factor: 27 in. to 14 in.

1970s developments
– 5.25 inch floppy disk form-factor (microcode
into mainframe)
– early emergence of industry standard disk
interfaces
ST506, SASI, SMD, ESDI
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Disk History
 Capacity of Unit Shown Megabytes; and
 Data density: M bit/sq. in.

1973:
Capacity: 140 MBytes
Density: 1. 7 Mbit/sq. in
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1979:
2,300 MBytes
7. 7 Mbit/sq. in
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Historical Perspective
Early 1980s: era of PCs and first generation
Mid 1980s:

workstations; and
era of Client/server computing and
Centralized storage on file server

This voyage of computing from first generation to
client/server resulted in end of proprietary
interfaces and:
Accelerated disk downsizing: 8 inch to 5.25 inch
Mass market disk drives become a reality
industry standards: SCSI, IPI, IDE
5.25 inch drives for standalone PCs,
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Historical Perspective … Cont’d

Late 1980s - Early 1990s:
Era of Laptops, note-books, (palmtops)
– 3.5 inch, 2.5 inch, (1.8 inch form factors)
– Form factor plus capacity drives market,
Challenged by DRAM, flash RAM in PCMCIA
cards
still expensive, Intel promises but doesn’t
deliver
unattractive M Bytes per cubic inch

– Optical disk failed on performance but found
slot (CD ROM)

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Disk History

1989:
63 Mbit/sq. in
60,000 MBytes

1997:
1450 Mbit/sq. in
2300 MBytes

1997:
3090 Mbit/sq. in
8100 MBytes

A huge disk drive changed to palm-drive
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DRAM as % of Disk over time
MBits per square inch:
 In 1974, the use of DRAM was only 10% of the disk storage
 It reached to the peak in 1986 when DRAM was 40% of the
disk storage
 This trend once again started reducing and was up to 15%
in 1998
45%

9 v. 22 Mb/si

40%
35%
30%
25%
20%

15%
10%
5%

470 v. 3000 Mb/si
0.2 v. 1.7 Mb/si

0%
1974

1980

1986

1992

1998


Alternative Data Storage Technologies: Early 1990s
Technology

Cap
(MB)

BPI TPI
(Million)

BPI*TPI
Data Xfer

(KByte/s) Time

Access

150

12000

104

1.2

92

800

22860

38

0.9

3000

4600

43200

1638

71

492

1300

61000

1870

114

183

1200

33528

1880

63

3000

Conventional Tape:
Cartridge (.25")
min.
IBM 3490 (.5")
sec.

Helical Scan Tape:
Video (8mm)
45 secs
DAT (4mm)
20 secs

Magnetic &
Optical Disk:
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Devices: Magnetic Disks
Purpose:
– Long-term, nonvolatile storage
– Large, inexpensive, slow level in the
storage hierarchy
Characteristics:
– Seek Time (~8 ms avg)
positional latency
rotational latency
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Devices: Magnetic Disks .. Cont’d
Transfer rate
– About a sector per ms
(5-15 MB/s)
– Blocks
Capacity
– Gigabytes
– Quadruples every 3 years
(aerodynamics)
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Devices: Magnetic Disks
Track

Response time
= Queue + Controller + Seek + Rot + Xfer

Sector

Service time

Cylinder
Platter
Head

 Speed: 7200 RPM = 120 RPS => 8 ms per rev
 Ave rot. latency = 4 ms
 128 sectors per track => 0.25 ms per sector
 1 KB per sector => 16 MB / s
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