1. IT Basics Secondary memory
Răzvan Daniel ZOTA
Faculty of Cybernetics, Statistics and Economic Informatics

2. Contents Secondary memory
Communication standards - PAN (Personal Area Network)

3. Secondary memory: Hard-disk SSD, flash disk CD-ROM DVD-ROM
Blue Ray Disk

4. Hard disk IBM – “Winchester” disk Rotation axis Read/Write head Track
Arm support
Read/Write head
Sector
Rotation axis
Track
Platan
Cillinder
IBM – “Winchester” disk

5. SSD (Solid State Drive)
SSDs do not contain, actually, disks nor other moving parts as in the case of classic hard disks. Known as “electronic disks”, the SSDs are using integrated circuits as storage capacity.
Nowadays there are many different technologies to accomplish this; the most important are the technologies based on DRAM and NAND flash memory.

6. SSD (Solid State Drive)
Comparative with the classic magnetic disks, the SSDs are running more quiet, there are resistant to physical shocks, have smaller latency times and much higher access times.
Currently, one big disadvantage is the price (approximately 6-8 times bigger per GB storage comparative to a classic hard disk).
Probably that in the near future these disks will replace the classic hard disks, in parallel with technology improving and price dropping.

7. CD-ROM CD-ROM Compact Disk, Read Only Memory
Very popular storage media initially built for storing audio data.
CD-ROM success is based on storage capacity, reliability and small price.

8. CD-ROM physical characteristics
The CDs have a diameter of 120 mm, 1,2 mm thick and can store up to 800 MB of information. They are built from a plastic layer, a reflective metal layer and a coat layer.
A CD-ROM unit is made of an engine, laser and rotation mechanisms and electronic circuits.
The engine of the unit is spinning the CD-ROM to the necessary speed as the laser assembly may read the information.
The laser assembly is made of a laser and optical lens; this assembly is reading the CD-ROM while it is spinning.
The rotation mechanism is made of an engine which position the lens in the correct position to access a certain area of the CD-ROM.
The electronic circuits manage the information transfer from the CD-ROM to the computer using a specialized communication bus.

9. CD-ROM
Reading speeds
The reading speed of a CD-ROM unit determines the transfer rate of data from the CD-ROM to the computer. The reading speed of a CD-ROM unit is a multiple of 150 kb and is followed by an “x”.
A CD-ROM unit denoted with 1x reading speed will read data with a speed of 150 kb per second.
Thus, a CD-ROM 10x will read 1500 kb per second, and so on.

10. CD writing There are two types of CD recorders:
CD-R – Compact Disc - Recordable represents the first available technology. The commercial CDs produced in high quantities are being made by a press. This technique make holes in the CD which are read by the laser beams.
The CD-R technology is using another strategy to write information on a CD. The CD-R add a colorant layer between the aluminium layer and the plastic one. This colorant layer is translucent and enables light to get to the aluminium layer from where it reflects back.
When a CD-ROM unit writes information on a CD-R it uses a laser to burn areas in the colorant layer to create opaque zones which do not reflect light.
When the CD is read, the laser assembly receive the reflection from the translucent areas. This surface is transforming the reflection/non-reflection in data bits. There are used two lasers: one for reading and one for writing. A CD-R unit with the characteristics of 24x/40x has a writing speed of 24x and a reading speed of 40x.

11. CD writing CD-RW – Compact Disc – Re Writable.
The CD-RW disk is different in the way that includes a state modifier layer between the plastic and the aluminium layer. This layer is composed by chemical elements which can modify its physical state at some temperatures.
When the writing laser beam is used to write information on disk, areas of this layer are melted by over heating and maintained in this state by a quick cooling. The melted areas are opaque and non-reflective.
For the CD-RW units there is a third laser beam: the erasing one. The erasing beam is used to bring back in a crystal state the specific layer. A CD-RW unit with the characteristics of 24x/12x/40x has a writing speed of 24x, a rewriting speed of 12x and a reading speed of 40x.

12. DAE
DAE - Digital Audio Extraction (DAE) – represents the process of copying an audio CD to another media (disk) by preserving original quality. This procedure is also known as "ripping“.
As a result of DAE process a .WAV file is created. Other formats as MP3 or Ogg Vorbis are using compression algorithms of these files resulting much smaller files with a minimal loss of quality.

13. DVD
DVD (Digital Versatile Disk) is the newer technology based on CD-ROM type technology. The DVD disks have the same physical dimension as the CD-ROM disks but they can store much more information.
The storage capacity is improved by a higher density recording technique and the access to more physical layers on the same media.
The DVD units are similar with CD-ROM units.
Some DVD players have audio decoders for Dolby Digital 5.1 (newer 7.1 or 8) or DTS (Digital Theater System).
The laser used in a DVD player is different from the one used in a CD-ROM unit.

14. DVD The DVD speed Speed Transfer rate Time for writing a
Single Layer DVD 1X
10.55 Mbit/s
1.32 MB/s
61 min. 2X
21.09 Mbit/s
2.64 MB/s
30 min. 4X
42.19 Mbit/s
5.27 MB/s
15 min. 8X
84.38 Mbit/s
10.55 MB/s
8 min.
16X
Mbit/s
21.09 MB/s
4 min.

15. DVD recording
DVD-R – DVD-R (Recordable) - similar with the CD-R technology (the disk can be written only once)
DVD-RAM – It is using “Random Access Memory” (RAM) technology enabling writing and rewriting a disk for times. DVD-RAM is using a technology similar with CD-RW with a 4.7GB data storage on each layer of the disk. The compatibility is a problem.
DVD-RW – The DVD-RW (Re-Writable) technology is made to solve the compatibility problem. It enables rewriting for approximately 1000 times.
DVD+RW – Similar with DVD-RW from HP and others.

16. CD vs. DVD Characteristic CD DVD Diameter 120 mm Thickness 1,2 mm
Distance between the tracks
1,6 mm
0,74 mm
Minimum length of the cavities
0,834 mm
0,4 mm
Wavelength of the laser beam
780 nm
640 nm
Capacity (of a layer)
0,64 GB
4,7 GB
Number of layers 1
1,2,3 sau 4

17. Blue Ray Disks – a comparison with CDs and DVDs
In 2002, the Blue-ray Disk Founders have announced the BD specifications, an optical big capacity storing format. In 2006 the BD 2.0 specification may store up to 25 GB (or 11.5 video hours - standard definition) on a disk with a diameter of 12 cm (same as CD and DVD).

18. CD writing formats
Phillips and Sony have begun developing the standard format for audio CD-s at the beginning of 1980’s.
The are two main types of standards for CD:
Logical standards
A logical standard defines the way of storing data on a CD. The CD-s and other disks are using tracks and sectors to store data. By the logical point of view, the standard represents the structure of the file system. The ISO 9660 (High Sierra) is a well known standard. The CD-s created with this standard may be accessed on the majority of platforms and operating systems.
Other formats are: Rock Ridge (UNIX), HFS (Macintosh) and hybrid HFS/ISO. Two standards that are improving the ISO 9660 standard are JOLIET and UDF. JOLIET is the Microsoft version for ISO 9660 which extends the maximum number of characters for a filename from 8 to 64. The Universal Disc Format (UDF) is another standard for storing data.

19. CD writing formats
Physical standards They are defining the writing mode (the place) of the data to the CD. Most of these standards are under the category of so-called “colored books”. When Phillips and Sony have brought the CD audio format, the first characteristics have been published in a book with red cover => Red Book.
Red Book – Compact Disc - Digital Audio (CD-DA), the format for audio CD-s; it specifies the mode of arranging songs in tracks on a CD.
Yellow Book – Initially developed as a data format; enables writing files on a disk.
Green Book – Phillips have created this format in 1986 for the new CD-I (Interactive). This format is specially made for audio and video data synchronization in the case of multimedia applications.

20. CD writing formats
Orange Book – This standard (1990) defines the physical format for the writable disks. It has three parts: 1 for Magneto-optic (MO) disks, 2 for Write Once (WO) disks and 3 for rewritable disks.
White Book – Is representing the MPEG1 audio-video recording format on a video CD (VCD).
Blue Book – This is the format for E-CD (Enhanced-CD) disks.

21. Data encoding and error control
Parity, Hamming codes and CRC (Cyclic Redundancy Check)
In the moment of a transmission we may have errors due to electro-magnetic interferences. The probability of an error bit for a microprocessor is estimated at approximately In case of a modern Intel microprocessor working with data at 109 bps (bits per second), this means that we must wait 109 seconds for producing an error, which is about 31,7 years!!
The detection/correction algorithms and techniques have been revived in the moment of CD-ROM and DVD appearance. The surface of the disks is deteriorating in time and it may become unusable if no data correction techniques would be used.

22. USB – Universal Serial Bus
At the beginning of 1990’s there was the necessity of developing a new standard for serial interfaces. There was a need for a connecting device without a manual reconfiguration, without rebooting the computer, without a PCI component for each device, using a single universal connector and cabling with no external power supply.
The bandwidth of the USB port is of 12 Mbs/sec, shared for all attached devices, the limit being of 127 devices (because of the address space limitation). The cable with 4 wires is using 2 wires for data transmission and the other two for power supply (5V and 0V).
The USB 2.0 enables the following data rates:
Low-Speed – 1,5 Mbps
Full-Speed – 12 Mbps
Hi-Speed Mbps
(The USB 3.0 standard has speeds up to 5 Gbit/s MB/s)
Corecta inter-comunicare se face cu ajutorul a două tipuri de mufe (master/slave). Proiectarea comunicaţiei USB se face pe baza unei topologii arbore cu „hub routers” ca noduri. Pentru a satisface această schemă ierarhică, echipamentele USB sunt deseori echipate cu mai multe prize pentru a accepta conexiunile mai multor ehipamente USB. Există definite 3 entităţi de tip USB: USB host, USB hub şi unitatea funcţională conectată. Gazda (host) este de regulă, PC-ul. Hub-ul poate fi de sine stătător sau înglobat într-un dispozitiv periferic ce oferă, de asemenea, funcţionalitatea respectivă.
Interfaţa USB funcţionează pe baza protocolului master/slave.
Definitia protocolului: un protocol defineşte formatul şi ordinea mesajelor schimbate între două entităţi ce comunică între ele, precum şi acţiunile ce sunt întreprinse odată cu transmiterea sau recepţia unui mesaj sau a unui alt eveniment.

23. IEEE 1394 (Firewire) and Thunderbolt
IEEE(Institute of Electrical and Electronics Engineers) (Eye-triple-E)
External standard interface for quick data transfers (up to 400 Mbps for 1394a and 800 Mbps for 1394b). The physical interfaces for IEEE 1394 standard have different names, depending of the producer. Apple (the first developer) is using FireWire name. Other names include: i.link (Sony) and Lynx (Texas Instruments).
Thunderbolt (2011) is another hardware interface for connecting external peripherals to a computer, developed by Intel. In 2011 Apple introduced for the first time this technology on MacBook Pro
Thunderbolt 2 (2013) is the second generation with speeds up to 20 Gb/s while Thunderbolt 3 is expecting to deliver data at speeds of 40 Gb/s.

24. Bluetooth
Bluetooth – industrial standard for PAN (Personal Area Network) wireless networks. Bluetooth is offering the connection possibility for: mobile/smartphones, laptops, PC-s, digital cameras, video consoles, audio equipment. The Bluetooth specifications are developed under the auspices of Bluetooth Special Interest Group.
Class
Distance (approx.) 1
~100 meters 2
~10 meters 3
~1 meter

25. Bluetooth
Bluetooth is using short-wavelength UHF radio waves in the ISM Band from 2.4 to 2.485 GHz. The radio technology used is called frequency-hopping spread spectrum (FHSS).
Version
Transfer rate
1.2
723.1 Kbit/s
2.0 + EDR, 2.1
2.1 Mbit/s
3.0
4.0+LE (Low Energy)
5.0 ( ) new features for IoT
Up to 25/50 Mbit/s

26. (Legacy) parallel interface
The PC parallel port is using a DB-25 connector.
It is called Centronics interface (Epson).
SPP 100 KBs (O) software controlled
New types of parallel ports:
EPP (Enhanced Parallel Port) 1MBs (I/O) Controlled by hardware circuits
ECP (Extended Capabilities Port) - 5 MBs (I/O) - DMA control with FIFO
Same connectors with 50 times faster speeds

27. (Legacy) parallel connectors

28. HDMI connectors HDMI – (High Definition Multimedia Interface)
Audio-video interface for video and audio digital data transfer between devices
Interface replacing analog video standards