Marking
Action to highlight a graphic element or part of text by modifying its visual attributes.
English: highlighting.
MBMS
Unlike DVB-H or MediaFloThe MBMS (Multimedia Broadcast Multicast Service) is rooted in cellular technologies and theUMTS. A cellular network is not suitable for broadcasting of: distributing a film to x users x is equivalent to using both the resource.
Based on the current UMTS networks (multiplexing type W-CDMA), the cost of deployment would be very low even if the mobile terminal should be adapted (in software or hardware depending on the scenario). In addition, an uplink channel may be used for returns and interactive service. This technology implements a multicast mode (dissemination a limited number of users) and a broadcast mode (broadcast to all users of the cell in question).
Level flowSharing the UMTS band of 5 MHz, the data rate is estimated at 384 kbps (equivalent to 3 chains encoded in low resolution at 128 kbps each). It appears therefore that its use be limited to video content lighter than the standard type T-DMB or DVB-H.
Testing and deployment
Standardization of MBMS is provided by working groups 3GPP which depends on the UMTS. The first standards are defined in Release 6 of UMTS (end 2004).
No test took place at the moment, but the former are expected this year.
MBR
The hand boot record (MBR) is the first physical sector of every disk. It contains in its 512 bytes crucial information on the support structure and any alteration of its content usually makes the disc unreadable.
At the start of a computerWhen the BIOS has finished its initialization sequence (POST = Power-On Self Test) The last statement it executes sends the playhead to read the content of this sector on the disk that the BIOS has registered as a startup disk. The rest of the computer behavior is dictated by the information contained in the MBR. The content is comprehensive from the end of the sector because, paradoxically, is more logical in terms of function.
Firstly the computer identifies the presence of the last two bytes of the number 55AA (hex) also called "mark of the executive branch." In the absence of this marker operations could continue.
* Then just 64 bytes that make up the table partitionsThat is to say, indicating the number of partitions on the disk and its location.
4 bytes contain the digital signature disk that is assigned at format time and is included in many keys to the registry.
* One hundred bytes (varies by language) are assigned to the text of error messages at boot (partition table invalid, Missing operating system ...).
Finally the first 300 byte sector contains executable code which is of prime importance.
Indeed, after noting the presence of the marker 55AA computer running this code. In a first step the code load Memory partition table, the benchmark in reading what is the active partition (the partition containing the operating system) and sends the computer read the boot sector (= boot, not to be confused with the MBR) of this partition .
Boot sector of a partition
He must be aware of each NTFS partition contains 16 reserved areas (the last 9 are not used). The first is the boot sector itself. As the MBR contains the marker 5AA, executable code, information on the structure of this partition and error messages (including the notorious "NTLDR missing").
The executable code loads the partition information and will read more of executable code that is in the following 6 sectors. This code is the bootstrap which will in turn start executing the file NTLDR (NT Loader: the "shipper" of Windows). This NTDETECT.COM then load all files from Windows
Any alteration boot sector of a partition will lead to failure. Depending on the nature of the changes the error message will be different. In particular the message NTLDR is missing does not usually that the NTLDR file is missing, but it has not been found after a change in the boot sector. Of course, the bootstrap is used only for the system partition.
The structure is somewhat different for a FAT partition, but the general principles are the same. Finally there is a backup boot sector in each partition.
Some remarks
Alterations of the MBR can be repaired by the instruction executed fixmbr from the recovery console CD Windows. This instruction rewrites the executable code and the 55AA marker. It does not change the partition table that contains the sector.
There are a number of years various virus have benefited from the presence of executable code in the MBR to settle in its place and will start and before the operating system. During infection the virus placed a copy of the MBR sector on a disk arbitrary. After running the virus would read the copy, which in turn launched the operating system so that everything seemed to proceed normally. The classic recipe was then given (for DOS and Windows versions 95.98 and Millennium) was to execute the command FDISK / MBR (fixmbr or for versions of Windows) to restore the MBR. This solution works only if the virus code does not extend to the space containing the partition information. If the space for this information is changed, restored the MBR does not fetch a copy of the original sector made by the virus because he alone knows where it was placed. Therefore the HDD is no longer available. The only solution to repair a virus was to pick up a copy of the sector (with the partition table intact) to replace it in the MBR.
Recently a rootkit using the old technique of MBR infection was observed. In his case FIXMBR working properly because the code does not alter the partition table. It is not clear that it will be the same for the following.
Alterations of the boot sector can be repaired by the fixboot command (first thing to deal with an error indicating a problem with NTLDR).
Finally the utility TestDisk can repair most failures due to an altered MBR or boot sectors, particularly those involving a symptom distressing: the disappearance of a partition or the existence of a partition become unreadable.
MD2
(Message Digest 2)
Hash function sided designed by Ron Rivest, depending on a random permutation ofbytes.
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