3.5.5. Permanent Memory

For permanent (secondary) memory commonly used PC floppy disk device, a hard disk and an optical drive. USB stick has more elements of some communicable working memory than the properties of secondary memory. If it comes to a server is usually installed and the device with a magnetic strip and is supported by a RAID system. Each of the devices has a lasting memory installed your controller, whose function is to allow unambiguous identification of the device by the PC system regardless of the performance of internal devices.

Hard disk controller for PC, incorporated into the casing drive, get the name of the IDE (Intelligent Drive Electronics) is associated with the disk bus (e.g. ISA), using a simple card-adapter, which is tasked to achieve galvanic connection and possibly converting logical parameters in the limits identify the system. This card has the name of the ATA (AT Bus Attachment) and very often used the name of the AT controller or the AT bus controller, although it does not actually Controller. It is a CONTROL of floppy and disk devices. For it is possible to connect two and two floppy disk device, physical names [A:] and [B:] for the floppy device and the [C:] and [D:] for hard drives.

Enhanced EIDE (Enhanced IDE) standard supports an additional two physical devices that is included in the (secondary) disk channel, higher transmission speeds and diverse modes of operation. PCs typically have on the motherboard ISA and PCI bus and EIDE controller. CONTROL floppy and disk devices, regardless of whether it is made on a separate card or a chip on the motherboard, usually supports two floppies ([A:] and [B:]) devices on one channel, two EIDE devices ([C:] and [D:]) on the second channel and two EIDE devices ([E:] and [F:]) to the third channel. Devices can be hard disks, optical devices or devices with magnetic tape. One of the devices on the channel is configured as the main (master) and the other as an additional (slave). Ports of the device and the card shall be made within the computer chassis with multi-core cable with connectors for connecting printed circuit control devices and two channels, a bypass grafts is determined that the device is plugged in, which is the primary and which secondary (optional), and that his address and update address [A:] and [B:] drive. Depending on the speed of data transfer devices are usually marked with labels ATA33, ATA66, ATA100 and ATA133. As devices connecting flat multicore cable with 40 or 80 lines, and transmission of data over it is a 'parallel', this kind of interface is often also called PATA (Parallel ATA).

All disk space is not available to the user, it is divided for the following purposes:

             1. Boot sector 1, bar 0, side 0
             2. FAT table in sector 2, bar 0, side 0
             3. DIRECTORY structures in sector 3, bar 0, side 0
             4. Customer's premises for data

Schedule disk space is called ALLOCATION. The approach takes care of the data on the disk file system, where the performance and features related to the operating system that it is used and the purpose. So there is a system for recording on hard drives, optical media, databases and other types of devices. So Windows OS uses FAT and NTFS file system for disk devices.

The BOOT sector is used to initialize the load if the OS on a disk (floppy) present. FAT (File Allocation Table) table contains the locations of clusters on the disk belonging to individual files. The sector kept the original and copies of the FAT table (FAT 1 and FAT 2). Directory structure (directory) disc is kept in the third sector, and provides a table structure directory and every file that belongs to him. The remaining area taken OS and user's data (programs).

FAT contains a list of clusters, their number, for each file separately. Of course, different files can not have the cluster disk with the same number. As with PCs each cluster contains no information about the following, but are listed in sequence: FAT table, loss or alteration of data in a table practically means the loss of all data on the disk. The data is not overwritten sector by sector but by clusters. When the disk heads in one cluster data files are entered in all sectors in all areas of the cluster.

The concept of cluster operating system uses a PC as a basis for finding and reading files and is the smallest unit of data sets available on disk. Operating system when formatting the disk seeks its surface divided into as many clusters, which means that the size and number of clusters is proportional to the size of the disc and is not a standard fixed size. Cluster size ranges from 2 kB to 32 kB up to 65'536 (16 bits) clusters on disk partitions. In the special list - table called FAT (File Allocation Table), the PC operating system, keep the strings of numbers of clusters of each cache file individually. For example COMMAND.COM file is stored in clusters of 34, 35, 36, 231, 232, 243, 456 and 457. Losing data in this table is essentially the loss of all data on the disk. Imaginary area for viruses. It was often the target of FAT table naughty virus.

Every hard disk can be logically divided into smaller units so if the physical drive [C:] is divided into two logical parts in the process of the initial organization of the system, the first unit will be recognized as a logical unit [C:] and the other as a logical device [D:]. If there is one physical device labeled [D:] the second logical unit of the first physical drive [C:] will be assigned the next available drive letter first after tagging physical devices, in the above example [D:] becomes [E:]. The division into logical disk units is justified in older BIOS version that the community did not know the DOS recognize drives larger than 504 MB as a single entity, with improved versions of the BIOS does not recognize drives larger than 2 GB (32 kB × 65'536) because of limits in the size and number of clusters in the disk 16 bit FAT system of identification of clusters. Windows 95 with VFAT file system (32 bits) overrides this problem. A default cluster size FAT (FAT 16) the system is shown in the following table:

Significant change brings NTFS file system (New Technology File System), the truth only available for NT systems. Improves security by enabling encryption of files and folders and restrict access to your files. The smallest unit available for enrollment is also cluster. Data file stored in the MFT (Master File Table) table in which all of its required attributes. A default NTFS cluster size of the system also depends on the size of the volume:

One benefit of the system is NTFS format a partition (volume) with a cluster size of your choice and a number of attributes that can join the file, but the most important difference compared to the FAT is 'journaling' type of NTFS operating system, or the ability to turn off AutoRecover by violent computers. Records of changes in the work indexed and listed in the Journal on the basis of which is then recorded changes in files and prevents data loss and damage to the file system. More about that in the description of the Windows operating system.

Since the cluster is the smallest operating unit that the OS uses when writing files to disk, in large disks with a cluster size of 32 kB is coming up unused disk space for entry of small files. The unfilled cluster is not possible to continue with typing the following files to be used for a new one. As for this, usually can not be used 10-30% of disk space due to losses in enrollment of small files in large clusters.

Speed of access to data on the disk is largely dependent upon whether the disk controller connected to an ISA or local bus, and the available buffer in which to copy the entire cylinder or more of them about faster readings by first retrieving the data in that cylinder. The data transfer rate is typically about 1 MBps - 10 MBps depending on the type of control and the bus type for which it is attached. Buffer is usually setting initial system parameters determined from DRAM resources, but also have their own drives to control its internal buffer.

As the cluster is the smallest amount of space that can be accessed on the disk, recording data such as size of 3 kB in a cluster size of 8 kB will take it in its entirety and will remain inaccessible to 5 kB. Specifically in one cluster can not be written as two short files, because the fat in then both began with the same number of what OS will not allow it. Therefore, it is better that these clusters are as short as the loss of unused space as much as possible.

As for this, it is easy to understand the advantages of FAT 32 and similar systems writing to disk, and the Windows 98 and Windows 95b cluster size is 4 kB of disk capacity of 256 MB - 8 GB, eight times less disk capacity of 2 GB compared to FAT 16 and a better utilization of disk space. NTFS offers better performance. New product is ReFS (Resilient File System) file system which maximizes data availability and integrity, provide scalability and performance and better detect and repair problems. On-disk structure is reliable and scalable. ReFS does not support short file names of type file_n~1.txt. Intimate necessity for removable media, like a stick or memory card, designed exFAT (Extended File Allocation Table), which is sometimes referred to as the FAT 64. Differences for specific Windows operating systems are shown in the following table.

Unstoppable penetrating new conception access non-volatile memory that uses the fast SATA (Serial ATA) disk access technology and PCI-Express bus, with much better features. SATA interface uses 8 lines as opposed to the older parallel IDE cable that is used 80 pin connectors (40 pins for data and 40 for GND) and where the degradation of the signal at the interface between the main problem. Serial connections reduce the complexity and communication protocol, reducing the number of required contacts. This allows a data transfer rate up significantly, particularly in the version of SATA-III (about 6 Gbps). Serial architecture uses PCI-Express also the reduction of the complexity of the communication protocol to increase the data rate. Make no mistake, PATA and SATA are the ways in which access to the device with regard to the exchange of data, and the file system on the other hand how the data is organized on the access medium, and how the records and read from media.

SATA is not just a feature of built-in disk systems. Four SATA external port on the PCI card with integrated RAID support to enable the connection of drives in the field who are 'out' casing. Optical DVD drives are also increasingly made with SATA interface (SCSI and CD-RW once). As disk drives, optical drives have their own storage system - UDF (Universal Disk Format). UDF is a standard created at the end of the last millennium, and its growing popularity thanks to CD-RW and DVD-RW media.

During its development, UDF has undergone revision 1.02 (1996), 1.50 (1997), 2.0 (1998), 2.01 (2000), 2.50 (2003) and 2.60 (2005). ISO, El Torito, or Joliet gradually abandoned, although it will need to add Joliet compatibility if you want to read the contents of the Windows 9X OS. The main purpose is to optically RW behaves when writing a floppy disk, or you can write and delete files as it is a recording to disk or disk. If you want to read the data from a DVD-Video device, the data on the media must be in standard supported by the product if they want to watch on it. So be careful who UDF format DVD video player uses (usually first, 1.02). So, the DVD video player supports media that has records in the UDF were DVD-R or DVD-RW.

When entering data on a CD automatically generate TOC (Table Of Contents), which contained the whole structure and the start address of the recorded tape. DVD home address recorded in the DVD structure. Each bar contains a contiguous sequence of data block size of 2048 b or 2352 b, depending on whether the file or record audio features. The concept of multi-bar means that the CD player can capture data in one bar or more bars within a session that describes the TOC. Adding each new session, a new added following new TOC (the old TOC are not deleted) that contains the latest index of previous sessions. So, for example, an audio CD has one session with 16 bars on the principle: each bar one song. It can also be combined to one sessions with multiple types of audio bar, and other data from one tape and the CD is not finalized about the further addition of session and create a new TOC. File data is usually in one bar per session. In short, TOC describes how the session and edited bar, 'file system' describes the files and folders inside the bar file type. Attention, only the first session will be audio sessions. So, as far as the storage of file data, it is not necessary that the media immediately bolted for further correspondence file data to the new session.

Methods for preparing data and their 'saving' the media are very diverse. The CD is limited to 99 bars and DVD on the 191 bars, and bar itself has 300 or more blocks. DVD TOC but no DVD STRUCTURE translates into shape while reading the TOC content. TOC and DVD STRUCTURE entered in the lead-in of the session with which each session starts. Each session concludes LEAD-OUT marks the end of a session.

An interesting story is RW media type that allows to record a CD / DVD for disposable wipes to re-enter or formatted to work on the principles of the diskette device. To RW could not be used as a floppy disk to a Windows XP OS enough its original installation, which knows how to read the content but does not know to prepare (format) RW for that kind of use. For this purpose, should have more complete (FULL) version of the program to work with CD-RW or DVD-RW media, such as DirectCD, InCD and later that are not exactly cheap. Quality program support is more expensive than the optical device. You can not not mention that most of the Linux 2.6.x system supports read and write to all of the above UDF.

Best features about the durability of data has a DVD-RAM media which 'closed' in the body that is inserted into the machine, along with the media, like floppy device (type 1), although there are solutions where it is used as other media (type 2). It has a capacity of 4.7 GB / 9.4 GB. Lets around 100'000 writing, which is about a hundred times more than the standard RW media. Can be a good solution for backing up data in a version with a USB 2.0 interface, so portable outdoor unit. Of course, it uses UDF format data logger. In addition to the computers, it can be found in the TV-video devices.

SUMMARY:

New magnetic medium, regardless of whether it comes to floppy or hard drive, you need to PREPARE prior to use for data - FORMAT. If the magnetic media hard drive in preparation for the reception of data, partitioned (FDISK) - logical units, each logical unit for recording media, which belong to the letters [A:] or [B:] for the floppy devices and their media or [C:] to [Z:] to disk partition or optical devices (only RW media) should be formatted. The process of formatting a floppy disk is shown in the next printing.

             C:\>format A:
             Insert new disk for drive A:
             and press ENTER when ready...
             The type of the file system is FAT.
             Verifying 1.44M
             25 percent completed
             :

             Initializing the File Allocation Table (FAT)...
             Volume label (11 characters, ENTER for none)? damaged
             :
             Format complete.

             1'457'664 bytes total disk space.
                49'152 bytes in bad sectors.
             1'408'512 bytes available on disk.

             512 bytes in each allocation unit.
             2'751 allocation units available on disk.

             12 bits in each FAT entry.

             Volume Serial Number is FCDB-D62E

             Format another (Y/N)? n

             C:\>

The format is similar to that in most operating systems. Operating system when preparing media may encounter physically damaged or defective media technology, which can not be prepared for the reception of data and in the end found a format mark bad sectors in the FAT table as unavailable. It used to be common to the hard disk contains a few percent of inaccessible sectors. Each partition has its identification number (Volume Serial Number) generated by the random process. Fill in the correct media will not have a row of 49'152 bytes in bad sectors, and instead of 'total=bad+available' will be 'total=available'.

BIOS of PC via its address scheme (Table 3.5.16) can detect up to four physical devices on which to organize the data partitions. For disk partitions can be primary or extended. Primary partition can be formatted and immediately prepare to accept data, while in the extended partition should be declared logical partitions. An extended partition is not directly reachable only by its logic defined parts and essentially a container of logical partitions that can be prepared to accept data. If the entire disk voted as one primary partition that would mean that you can use 4 physical disk or a single physical disk can be divided into a maximum of 4 primary partitions of my financial reach. Only one partition on the disk that would be an extended partition can not be created. Media must have one primary partition, which is declared just starting (active) if it was installed by the operating system.

As for this, do not need all 4 disk partitions declared only as primary and thus prevent further enlargement. Just on a single physical disk one primary and one extended partition where you can 'enforce' a number of logical partitions, depending on the operating system. In Windows systems the number of logical partitions depends on the number of remaining available characters, and similar case is for Linux systems. We should not be afraid of logical partitions. It's just one extra point located on the disk, which acts as an extension of records BIOS. Mechanism of logical partitions is established because of the need to work with more than 4 'device' that can accept work with the data, as is the case when the physical disk capacity for larger addressing capabilities of the file system. SATA concept solves this problem with additional possibilities for the control electronics specified in the next chapter.

Some optical media are not exempt from this procedure format, CD-RW or DVD-RW needs to be formatted if you want to use as a UDF (Universal Disc Format) prepared by the media to behave analogously diskettes, at will erase and write them (packet writing). However, despite these possibilities this type of media is most often used as a common medium for write-once and, in case of need 'deleted' and prepare for the new record, because the procedure is simple and does not require specialized programs that know how to work with optical media like a floppy.