In the early 1980s, SCSI-1 has 8 channels of data and operate at a speed of 5 MHz, or a data rate of 5 Mbyte / sec. SCSI-1 now allows up to seven devices to be connected in daisy-chain and connected to the host system. Signal and Phase For any of these cases, all activities on the bus going in the series of phases. Phase are: Bus Free: indicates that there are no devices that use the bus Arbitration: allow a device to gain control of the bus. Selection: select the target to allow an initiator to form a function. Reselektion: allow targets to connect again with the initiator to continue operations. Command: allow targets to request information from the command initiator. Data: the data transfer request to allow the target to the initiator of the target. Status: to allow the target to request information sent from the status of the target to the initiator. Message: allow targets asking for a transfer. SCSI timing When a device id or more states during the arbitration phase, the device has the highest priority will memeangkan competition. Setlah a perngkat won the arbitration becomes an initiator tresebut. This device akakn phase selection signal SEL dengsan states. After that, the target indicates that he has entered a phase of command by asserting the channel C / D; these channels will be stressed during this phase. Target then asserts REQ to request the first byte inisitor command. After receiving and interpreting commands the target, the target placed on the bus In the data phase by eliminating the channel C / D and confirms the channel I / O. Terkhir, putting a target on the bus by asserting phase mesagge In MSG channels and move messages containing byte Command Complete message. Command The command specified in the command descriptar block (CDB) provided by the initiator. After konoksi between the initiator to the target has been established, the initiator will move through the data bus CDB to start iksekusi command. Standard SCSI-2 includes the commands to type pearngkat below: Direct-access devices Sequential-access devices Printer Professors Write-one device CD-ROM Scanner Optical memory devices Medium-displacement devices Komunukasi device P1394 Serial Bus P1394 has some advantages compared with a SCSI interface and I / O other. P1394 is very fast, inexpensive, and easy to implement. Interference P1394 One of the advantages is that it uses a serial transmission (bit per bit) instead of parallel. In addition, the physical size of the computer even with the development of computational capabilities and the needs of I / O though. Configuration P1394 P1394 uses a daisy-chain configuration, with a capacity up to 63 perngkat connected. P1394 provides the ability of the so-called hotplugging, which allows to connect or disconnect a peripheral anpa have to turn off the computer first or merekonfigurasi ualng system. Physical Layer P1394 physical layer describes some alternative media and the plug-connector, with the physical properties and other data transmissions. Determined from the data speed of 400 Mbps higga 25. Physical layer convert binary data into electrical signals for a variety of physical media. Leyer also provides arbitration services which ensures that only a device that will be menstransmisikan data at a time. Link Layer Link layer defines the transmission of data in packets. Two types of transmissions are supported: Asyncronous: number of data changes and a few bytes of information transection layer on the move as a package to an address of an explicit and an acknowledgment will be returned. Asochcronous: amount of data transferred changing preformance form a fixed-size packets are transmitted at regular intervals. Subaksi consists of five time periods: Arbitration Transmission: this is an exchange of signal required to provide a device control bus. Packet Transmission: each packet includes a header that contains the source ID and destination ID. Acknowledgment Gap: this is a time delay for the purpose to receive and decode the packets and give acknowledgment. Acknowledgment: pengembalikan an acknowledgment packet receiver with a code indicating the action to be taken by the recipient. Subaction Gap: this is an idle period to ensure that other nodes on the bus did not initiate arbitration before paker acknowledgment is transmitted.