computer architecture (p175b125) assoc.prof. stasys maciulevičius computer dept....

COMPUTER ARCHITECTURE

(P175B125)

Assoc.Prof. Stasys Maciulevičius

Computer Dept.

[email protected]

©S.Maciulevičius 22009-2013

Virtual memory

Modern computers can simultaneously run several programs (in parallel or pseudoparallel mode)

Each such program (process) has a separate code and data area

The mechanism that provides for more processes run simultaneously, sharing the memory correctly and correct addresing of information, transforming logical addresses to physical addresses is called Virtual

Memory


Virtual memory

Moreover, the virtual memory ensure that the necessary for process information (program code and data) at the appropriate time would be loaded in the main memory, protects the process memory space from other processes

Virtual memory in physical point of view - the main memory plus part of the external memory, together with the tools for address transforming and information interchanging between these levels

Virtual memory in logical point of view - extended memory space with contiguous addressing


Virtual memory

There are two main principles used in realization of virtual memory:

1) Segmentation - an application's virtual address space is divided into variable-length segments. A virtual address consists of a segment number and an offset within the segment. Task may have several segments – code (program), data, stack.

2) Paging – an application's virtual address space is divided into fixed sized pages; a page is a block of contiguous virtual memory addresses, usually at least 4Kbytes in size. The pages do not have to be contiguous in memory


Main and external memory

CPU reg.

Swap insegment

(page)

Cache

Main memory

External memory

Swap outsegment

(page)


Segmented virtual memory

Op. system

1’st process

2’nd process

3’rd process

4’th process

5’th process

Op. system

2’nd process

3’rd process

4’th process

5’th process

Op. system

2’nd process

3’rd process

5’th process

Op. system

2’nd process

3’rd process

6’th process

5’th process


Segmenting

Segment No. Byte address

31 24 23 0

Segm.No. 32-bit base

0 20000H 1 4F000H 2 8000H … ….

Memory

2 segm

0 segm.

1 segm.

8000

Segment table

4F000

20000248


Simple mechanism of segmentation

Stack length

Data length

Program length

MUX

Stack base

Data base

Program base

MUX

Page faultCompa-rator

Offset

Segment

Sum-mator Physical

address


Segmentation principles in IA-32

Selector Effective address

15 0 31 0

Descriptor table

Segment descriptor +Base address

Linear (physical) address31 0


Segmentation mechanism in IA-32

In IA-32 architecture segmentation is supported by folowing tools:• mechanism for calculation of physical address• segment descriptor tables:

• local descriptor table (LDT)• global descriptor table (GDT)• interrupt descriptor table (IDT)

• privilegy system

Each table has assigned to it the processor register, which holds:• 16-bit limit (size of table)• 32-bit base address (table location in memory)


Address spaces in IA-32

IA-32 architecture has three such address spaces:• logical address space; logical (or virtual) address

consists of two integers: a 16-bit segment selector and a 32-bit offset; space size is 214 selectors 4 GB = 64 TB

• linear address space; linear address appears on the output of segmentation unit, as result of logical address translation;

• physical address space; physical address appears on the output of paging unit; in case when paging is not used, physical address equals to linear address; this address (BE7-BE0 bits and A31-A3) goas to main memory


Simple mechanism of paging

Page table

Logical page number Byte offset

Page frame number Byte offset

Protection bits


Segmentation with paging in IA-32

Selector Effective address (offset)

15 0 31 0

Segmentation unit

Physical address31 0

Descriptor’s index

Paging unit

(optional)

14

32

32

32

Linear address


Segmentation mechanism in IA-32


Paging in IA-32

Page table

Directory Page No. Byte offset

Linear address

Page directory

PDE

PTE

Page (4 KB)

Target10

10 12

CR3 (PDBR)Control register(Page Directory Phys. Base Address)


Address translation

Transformation of virtual address to physical is address translation.

The problem - the extra step – access to page table. How to speed up the memory access?

1. To store whole page table in processor - is unrealistic because the page table takes a lot of place - megabytes. For example, if the page size is 4 KB, a 4 GB of memory takes 4 GB / 4 KB = 1024 K pages!

2. To store part of page table in special cache in

processor. Each entry in this cache ensure fast access even to 1000 words


Translation lookaside buffer (TLB)

Page

table


Page frame number Byte offset

TLB

ORPage not in main memory

Effective address from CPU

Miss

Load TLB

Hit

Page swap with hard disc

Physical address to main memory


TLB and cache

Physical address

Tag

Byte No.

Hit

Hit

Hit

Data line


Cache

Effective address

=?

=?

Byte

TLB

Index Index


Memory management unit

A memory management unit (MMU) is a computer hardware component responsible for handling accesses to memory requested by the CPU

Its functions include:• translation of virtual addresses to physical addresses

(i.e., virtual memory management)• memory protection• cache control• bus arbitration, and, in simpler computer architectures

(especially 8-bit systems)• bank switching


AMD K7 microarchitecture


Parity checking

A parity checking refers to the use of parity bits to check that data has been writted and readed accurately

The parity bit is added to every data unit (typically byte)

The parity bit for each unit is set so that: unit has either an odd number or unit has an even number of set bits


Parity checking

k = b0 b1 … b7 ork = 1 b0 b1 … b7

0 1 0 1 0 1 1 0 k

Data bus

Error

Data bus

Usually k=n/8

n

k

k

n

Address bus

1 1

Data

AR bytes DR

generating parity bits / checking

n

m Parity bits


Error-checking and correcting

Hamming code: a error-correcting code, can detect up to two simultaneous bit errors, and correct single-bit errors

Code length usually is k=log2n + 1;

With additional parity - k=log2n + 2Data bus

Error

n

k

k

n

Address bus

1 1

Data

AR bytes DR

Generating of Hamming

code

km ECC bits

Hamming check Error

Correc-tion

k

nn


Hamming codeBit Binary Contr. Data

12 1 1 0 0 D8 11 1 0 1 1 D7 10 1 0 1 0 D6 9 1 0 0 1 D5 8 1 0 0 0 K8 7 0 1 1 1 D4 6 0 1 1 0 D3 5 0 1 0 1 D2 4 0 1 0 0 K4 3 0 0 1 1 D1 2 0 0 1 0 K2 1 0 0 0 1 K1

Hamming code detects up to two simultaneous bit errors, and corrects single-bit errors


Generating of Hamming code

K1 = D1 D2 D4 D5 D7K2 = D1 D3 D4 D6 D7K4 = D2 D3 D4 D8K8 = D5 D6 D7 D8

Let data byte is 00111001, bit D1 – at right. Then:K1 = 1 0 1 1 0 = 1K2 = 1 0 1 1 0 = 1K4 = 0 0 1 0 = 1K8 = 1 1 0 0 = 0

Data byte is saved im memory with control bits:

001101001111


Error correction

Let error occus, e.g., instead:001101001111

we have001101101111

Calculate Hamming code:K1 = 1 0 1 1 0 = 1K2 = 1 1 1 1 0 = 0K4 = 0 1 1 0 = 0K8 = 1 1 0 0 = 0

Use sum mod2: K8 K4 K2 K1

0 1 1 1 0 0 0 1 0 1 1 0 – this is number of fault bit


Error correction: redundancy

Single error correction

Single error correction,

double error detection

Data bits

ECC bits

Redun-dancy, %

ECC bits Redundancy, %

8 4 50,00 5 62,50

16 5 31,25 6 37,50

32 6 18,75 7 21,88

64 7 10,4 8 12,50

128 8 6,25 9 7,03

256 9 3,52 10 3,91


External memory

As long-term storage in computers are used:

hard drives CD-ROM, CDs (optical compact discs) DVDs flash memory floppy disks (outdated) strimmers.


External memory


External memory

Access modes: direct access sequential access

Parameters: capacity access time data transfer spped relative price


First HD

IBM announced the IBM 350 storage unit as a component of the RAMAC 305 computer system on September 13, 1956

Assembled with covers, the 350 was 60 inches long, 68 inches high and 29 inches deep

It was configured with 50 magnetic disks containing 50,000 sectors, each of which held 100 alphanumeric characters, for a capacity of 5 million characters


First HD

• 50 platters• 1 head


First HD

Disks rotated at 1,200 rpm ; tracks (20 to the inch) were recorded at up to 100 bits per inch, and typical head-to-disk spacing was 800 microinches

The execution of a "seek" instruction positioned a read-write head to the track that contained the desired sector and selected the sector for a later read or write operation

Seek time averaged about 600 milliseconds


Hard disk drive


Hard disk drive

Platters vary in size and hard disk drives come in two form factors, 5.25in or 3.5in

Typically two or three or more platters are stacked on top of each other with a common spindle

Tthe head flies a fraction of a millimetre above the disk. On early hard disk drives this distance was around 0.2mm. In modern-day drives this has been reduced to 0.07mm or less

There's a read/write head for each side of each platter, mounted on arms


Hard disk drive

The disk controller controls the drive's servo-motors and translates the fluctuating voltages from the head into digital data for the CPU

More often than not, the next set of data to be read is sequentially located on the disk. For this reason, hard drives contain between 256KB and 8MB of cache buffer in which to store all the information in a sector or cylinder in case it's needed. This is very effective in speeding up both throughput and access times


Technical specifications

Capacity: Amount of data which can be stored on a hard drive

Transfer rate: Quantity of data which can be read or written from the disk per unit of time. It is expressed in bits per second (Mb/s)

Rotational speed: The speed at which the platters turn, expressed in rotations per minute (rpm for short). Hard drive speeds are on the order of 7200 to 15000 rpm. The faster a drive rotates, the higher its transfer rate. On the other hand, a hard drive which rotates quickly tends to be louder and heats up more easily


Technical specifications Latency (also called rotational delay): The length

of time that passes between the moment when the disk finds the track and the moment it finds the data

Average access time: Average amount of time it takes the read head to find the right track and access the data. In other words, it represents the average length of time it takes the disk to provide data after having received the order to do so. It must be as short as possible

Radial density: number of tracks per inch (tpi). Linear density: number of bits per inch (bpi) on a given track. Surface density: ratio between the linear density and radial density

(expressed in bits per square inch).


Technical specifications

Cache memory: Amound of memory located on the hard drive. Cache memory is used to store the drive's most frequently-accessed data, in order to improve overall performance

Interface: the connections used by the hard drive. The main hard drive interfaces are IDE/ATA, SATA, SCSI


Information on disk


Information on disk

The data is organised in concentric circles called "tracks"

The tracks are separated into areas called sectors, containing data (generally at least 512 octets per sector)

The term cylinder refers to all data found on the same track of different platters

The term clusters (also called allocation units) refers to minimum area that a file can take up on the hard drive


Hard disk

Formatted and unformatted disk capacity

Capacity = Number_of_cylinders Number_of_surfaces

Number_of_sectors/cilinder sector_size

Modern disk capacity is at least 500 GB, advanced disks even reach 4 TB


Hard disk

Access time depends on the following parameters:

cylinder seek time delay on the rotation transfer time

Information transmission time depends on: recording density and disk rotational speed


Old disk - MD Maxtor 33073H3 Capacity 30 GB

Integrated interface ATA-5 / Ultra ATA/100

Buffer size/ type 2 MB SDRAM

Surfaces / Heads 3

Platters 2

Arreal density 14.7 Gb / sq. in. max

Track density 34 000 tpi

Linear density 354 - 431 kb/colyje

Bytes per sector/ Block 512

Sectors in track 373 - 746

Sectors in disk 60 032 448


Old disk - MD Maxtor 33073H3

Seek time (read op.)

Track-track 1.0 ms

Average 9.5 ms

Rotational speed(+ 0.1%) 5400 RPM

Data transfer rate To/from interface (Ultra ATA/100, DMA M5)

to 100 MB/s.

To/from interface (PIO 4 / Multi-word DMA M5)

to 16.7 MB/s

To/from medium to 46.7 MB/s

Start time 8.5 s


Recording methods

Traditional recording method –horizontal recording:

N S N S S N S N N S S N N S

Now a new recording method is in use – vertical (perpendicular) recording. The bits are in a vertical arrangement instead of horizontal in order to take up less space. By 2010, perpendicular densities are expected to exceed 500 Gb/sq. in.

N

S

S

N

S

N

N

S

S

N

S

N

S

N

N

S

S

N

N

S


Disk density

Disk Density is measured and is also called areal density

Now how is this density calculated? For the most part the density we measure in Bit per Inch (BPI) and track per inch (TPI)

When we multiply the TPI and BPI we get areal density

RAMAC had an areal density of 2,000 bit/in²


Disk density - 2008

In 2012 the highest areal density was around 625Gb/inch2. HDD areal densities measuring data-storage capacities are

projected to climb to a maximum 1800Gb/inch2 per platter by 2016, up from 744Gb/inch2 in 2011, as shown in the figure below

This means that from 2011 to 2016, the five-year compound annual growth rate (CAGR) for HDD areal densities will be equivalent to 19%

For this year, HDD areal densities are estimated to reach 780Gb/inch2 per platter, and then rise to 900Gb/inch2 next year.


Disk density


Disk capacity


Flash memory

Flash memory refers to a particular type of EEPROM (Electronically Erasable Programmable Read Only Memory). It is a memory chip that maintains stored information without requiring a power source

Flash memory differs from EEPROM in that EEPROM erases its content one byte at a time. This makes it slow to update. Flash memory can erase its data in entire blocks, making it a preferable technology for applications that require frequent updating of large amounts of data


Flash memory

Flash memory combines several useful features:

high packing density (the cell is 30% smaller than the DRAM)

maintaining stored information without requiring a

power supply erasing and recording information using electrical

signals low energy consumption high reliability and low price


Flash memory

Flash memory is used primarily as: rarely rewritten (eg, BIOS) memory compact exchangeable memory in computers (USB

keys) compact exchangeable memory in PDAs, digital

cameras, digital audio players etc.

E.g., Kingston DataTraveler 200 is 32GB-128GB capacity

(DataTraveler 300 – 256GB), has 20MB/sec read, 10MB/sec write speed

DataTraveler Vault has 256-AES hardware-based encryption, 2GB-32GB capacity


Solid state memory

Solid state memory or a solid state drive (SSD) is a device that uses no moving parts to store data

The first ferrite memory SSD devices, or auxiliary memory units as they were called at the time, emerged during the era of vacuum tube computers

In the 1970s and 1980s, SSDs were implemented in semiconductor memory for early supercomputers of IBM, Amdahl and Cray; however, the high price of the SSDs made them quite seldom used

RAM "disks" were popular as boot media in the 1980s when hard drives were expensive, floppy drives were slow


Solid state memory

2004: Texas Memory Systems' RamSan-325 can carry out 250,000 I/O operations a second.

Available in capacities of 128, 96, 64, and 32 gigabytes, RamSan-325 accelerates I/O intensive applications by delivering random data at sustained rates exceeding 1.5 Gbps

Non-volatile product has high availability architecture with redundant and hot swappable power supplies, redundant batteries

However, build using 512Mb of DDR RAMs, device was quite expensiv – 16 GB device costs $36.000


Solid state memory Now fash memory is media for building solid state

memory devices These devices can range up to 512GB (or even

more) Flash memory used as a hard drive has many

advantages over a traditional hard drive It is silent, much smaller than a traditional hard

drive, and highly portable with a much faster access time

However, the advantages of a traditional hard drive are price and capacity


SSD

Most SSD manufacturers use non-volatile flash memory to create more compact devices for the consumer market

These flash memory-based SSDs, also known as flash drives, do not require batteries. They are often packaged in standard disk drive form factors (1.8-, 2.5-, and 3.5-inch)

In addition, non-volatility allows flash SSDs to retain memory even during sudden power outages, ensuring data persistence

Flash memory SSDs are slower than DRAM SSDs and some designs are slower than even traditional HDDs on large files, but flash SSDs have no moving parts and thus seek times and other delays inherent in conventional electro-mechanical disks are negligible


SSD prices – some facts In March 2007 SanDisk announced it was offering its 32GB

2.5" SATA SSD to oems for $350. In July 2008 OCZ said its fast Core series 2.5" SSDs were available with an price of $169 for 32GB

October 2009: Active Media Products launched its Aviator 312 line of bus powered fast USB 3.0 external SSDs with R/W speeds upto 240MB/s and 160MB/s respectively. Capacity options include:- 16GB ($89), 32GB ($119) and 64GB ($209)

2013: Kingston SSDNow V300 Series SV300S37A/120G 2.5" 120GB SATA III Internal SSD - $102.99

SanDisk Extreme SDSSDX-480G-G25 2.5" 480GB SATA III SSD - $369.99


SSD and HD


Hybrid hard drive

Certain technology meets half-way between hard drive and solid-state drive, such as the hybrid drive, and ReadyBoost

A hybrid drive, sometimes called hybrid hard drive, uses a small SSD as a cache. The SSD is often flash memory

ReadyBoost is a part of the Microsoft Windows Vista operating system that uses compatible flash memory as a drive for a disk cache

A random disk read from the cache is generally 80 to 100 times faster than random disk read from a traditional hard drive

Hybrid hard drive

Controller

Flash memory

Hard diskInte

rface

Cach

e c

on

troller

Hybrid drive

2009-2013 S.Maciulevičius 61


Solid State Hybrid Drives


Adaptive Memory™ technology

Adaptive Memory™ technology from Seagate selectively tackles data that is frequently read and time–consuming to fetch. Seagate SSHD drives can then copy this data into the flash

Adaptive Memory technology makes such efficient use of the drive’s solid state memory that only 4GB to 8GB of flash capacity is actually needed. This reduces costs so much that it’s now practical to employ enterprise-class SLC NAND flash memory, the fastest and most reliable type of flash memory on the market


Intel Smart Response Technology

Smart Response Technology (SRT) is a proprietary caching mechanism introduced in 2011 by Intel for their Z68 chipset (for the Sandy Bridge–series processors), which allows a SATA solid-state drive (SSD) to function as cache for a (conventional, magnetic) hard disk drive

This provides the advantage of having a hard disk drive (or a RAID volume) for maximum storage capacity while delivering an SSD-like overall system performance experience


Intel Smart Response Technology

Time To Run Cold Boot Unigine Fallout 3 Photoshop Elements)

No SSD Cache 28 sec 40 sec 13 sec 19 sec

SSD Cache - Pass 1 23 sec 35 sec 13 sec 19 sec




computer architecture (p175b125) assoc.prof. stasys maciulevičius computer dept....

Documents

virtual memory slide

process memory space

process slide

processes virtual memory

program process

levels virtual memory

segmented virtual memory

realization of virtual