4. Data Storage Media
When considering storage media in role of digital
- Define the requirements of storage media for digital audio systems
- Define and compare the primary specifications of audio media
- Describe the basic architecture and operations of magnetic and optical
- Differentiate between "permanent" and "removable" media
and their uses
Chapter 5.1, Desktop
Audio Technology - Rumsey
- Media used for digital audio is not exclusive
to the audio world. Hard drives & Optical (DVD, CD) disks
are used for all types of computing.
- General computer
can be used in audio workstations.
- Earlier systems had dedicated media formats (SSL used gigantic data cartridges
for their automation storage)
- Current devices make special designs obsolete.
- Certain specifications must be met to ensure optimum performance
from a given device.
Storage media Requirements
Two main roles for storage media:
- Primarily, to record and replay in real time
- Secondarily, to provide backup storage
The task at hand can define the type of media used:
- Real-time recording and replay needs devices capable of
sustained data transfer for the specified number of audio
tracks, quick access to stored audio files, and the capacity to hold those
- Backup devices need not be real-time, but need to
have large capacity, should be removable, and should
be cheaper than primary media.
Disk Drives in General
Disk drives are the most common form of storage. Some
- They are random-access
- Data is stored either magnetically or optically.
- Media may be fixed or removable.
Removable Media vs Removable Drives
- Media is fixed if it cannot be separated from the
supporting hardware (motor, electronics, etc.). Hard drives
are the best example - the media is attached to the motor, cannot be separated.
- Media is Removable if the actual storage media (the
disk, tape, etc) can be removed from the supporting mechanics.
- Floppy disks
- CDs or DVDs
- Note: removable media is NOT the same as removable
- Removable drives contain the media and supporting
hardware (such as a hard drive sled or a firewire drive), but are still
considered fixed media.
- Removable media is the storage surfaces only.
- Drives consist of one or more disk surfaces on a common spindle
- rotation speed anywhere from a few hundred to several
- Speeds can be constant or variable, depending on the
- One or more heads are mounted on a positioning mechanism
which move the head(s) to locations on the disk.
- The heads read data from
or write data to the disk.
- The disk surface is divided into tracks and sectors.
- Tracks are concentric
rings on the disk.
- A cylinder is a collection of the same track
on multiple surfaces.
- A Sector is a section,
or "slice" of each track. Each sector typically holds 512 bytes
- Boundaries are defined by 'soft'
logical markers which are placed on the drive during the formatting process.
A drive's performance can be defined by certain performance
- published by manufacturers and
- can sometimes
when evaluating drives.
- sustained transfer rate - long-term data rate, sustained over many blocks. ore useful guide to overall performance.
- access time - time taken for a block of data to be accessed.
- Actual access time varies, depending on location of head and data.
- Access time is comprised of:
- seek latency (time to move head to the right track)
- rotational latency (time to roatet disk to the right block
on the track).
- The spec will read differently, depending on which test condition
- "Track-to-track" is the best number
- "average" is a more realistic guide to general performance.
- instantaneous transfer rate - the fastest speed which data can be read once the head has arrived at the correct location. This will indicate a drive's peak performance.
- storage capacity (formatted) - number of megabytes of available space after the drive has been
formatted. Formatting will decrease the capacity number since the format
information takes drive space as well.
The Winchester hard drive is the common
hard drive found in all personal computers. Features include:
- Magnetic system - binary data conveyed with polarized spots on magnetic
- Read-write memory (RWM)
- Large amounts of data in a small space
- sealed unit - disks are inaccessible, and contaminants
cannot come in contact with the disks
- Widespread popularity has allowed manufacturers to constantly improve performance
- access times <5 ms
- transfer rates over 3 GBps
- capacity upwards of 1 Terabyte (1024 Gigabytes)
- very affordable (under $100).
Number of different types of optical drives, but all
have common characteristics:
- removable media
- data is conveyed via changes in light, instead of
changes in magnetic charge
- written and read by a laser
- distance, or length of laser wave
- reflectivity of the surface (phase change)
- polarization of light due to magnetic state
- These two conditions can then represent binary data.
- pickup never touches media
- Several differences between optical systems:
- Data layout and density
- storage method changes from type tp type
- media is very inexpensive
- high density storage - high capacity for the size
- durable - data is (alledgedly) impervious to external
interference, such as magnetism
- Genrally slower than magnetic counterparts
- Generally not rewritable
- Read-only - commercial CDs
- Write-Once-Read-Many (WORM) - CD-R
- Read/Write - CD-RW, M/O drives
- Mass replicated molded discs
- Write once-read many
- Random access...
- Extremely portable, quick access
- Expensive per gigabyte
- Flash Drives generally not suitable for audio recording
SSD Solid state drives
- Random access, extremely fast access times
- Extremely fast read/write times, best suited for lots of files
- Expensive per gigabyte
- Poised to Replace Winchester magnetic hard drives
Removable Magnetic Media
- Types of media that be easily removed from a computer, making them good
for backups and mobility.
- Zip and Jaz (Iomega)
- Both capacity and speed are usually limited on these devices.
- Once handy for backup and transfer of data.
- Recordable CDs, DVDs and Flash Drives have made these devices virtually
RAID (Redundant Array of Inexpensive Disks)
- A means of connecting multiple Winchester drives together for improved
performance or reliability.
- Drives are connected in a array of 2 or more units, with data split between
- Several established RAID configurations:
- Distributed data (improved access times and transfer rates)
- Mirrored data (improved data reliability).
- Commonly found in servers
The Studer D-950 in used a RAID to mirror the computer's
drive and all data.
Tape Storage Media
- Linear access...slow
- Slow but inexpensive method of archiving massive amounts of data
- risk of obsolescence of hardware
- Tapes have much longer reliable life than optical or magnetic media
- have to be stored in safe environment away from magnetic fields/weather