| | | |  Tape Drive | | | | A device for the recording and playback of magnetic tapes. Drives can be of the helical or linear type, in which the tape reading /recording head touches or does not touch the tape respectively. Similar to a tape recorder, it accesses data in a sequential manner, i.e. it must read all the preceding data bolcks on the tape before getting to the data that is required. This means they are slow compared to other magnetic storage devices such as hard disk drives which allow for random access, however the speed deficit is offset by the fact that the media (tape cassettes) are cheap which makes it an ideal method for backups / archiving. In addition, whilst data access may be slow, the streaming of data to be stored to the tape can actually be very quick, with some drives managing 80MB/s or greater, that being comparable with hard disk drives. Tape autoloaders or libraries are devices incorporating a tape drive that are able to load and unload tapes automatically, making archiving and accessing large backups (or numbers or backups) easier. There are a number of interfaces used to connect the tape drive to a computer. The most common of these at present is the SCSI interface, however they may also be connected via Fibre Channel, IDE, Firewire, USB and more. The naming convention for tape drives is normally in terms of the maximum capacity of tape useable, with a 2:1 compression ratio. For example an 80/160 drive can store 80GB of data uncompressed or 160GB with a compression ratio of 2:1. | | | | | | Firewall | | | | A hardware or software-based device used to protect a computer or network from access by unauthorised users. The term is derived from i) the firewalls used in building construction to stop the spread of fire by isolating parts of a building at critical points ii) the practice of firefighters of clearing part of a building or forest to remove combustible materials creating a barrier. An example of hardware incorporating a firewall is a modern router (firewalls work in close conjunction with router software) - there are also stand alone firewall devices. Software firewalls are available on a buy-then-subscribe basis, where the software is initially purchased with free security updates included for a year (typically). This is then often followed by a paid subscription structure, to be eligible for further updates as and when they are released. They are sometimes also offered as freeware in the form of a "lite" version of the subscription package. All traffic into and out of the network must flow through the firewall. Data packets are inspected to determine whether they are to be allowed or not - the rules determining which data packets are allowed through the firewall and which are denied access are set during the configuration of the firewall. A number of different methods are used to determine what happens to a data packet and these have evolved over time as firewalls have become more sophisticated (partly driven by the need to cope with increasingly sophisticated hackers!), as follows. Packet filters look at each data packet and it's contents in isolation and independently of the data stream it is a part of. Stateful filtering not only looks at the packet contents but also, by maintaining records of all connections, is able to compare the packet with those from known and/or trusted sources and in addition to determine whether it is part of an existing data stream or a new connection. Application layer filtering was the third major development - also known as proxy filtering - and the most sophisticated because it can recognise protocols and the way they are used and detect irregularities and suspicious activity (up to a point). Ultimately however, any firewall is only as effective as the way it has been configured. A badly configured firewall can be more or less useless, with many users failing to fully grasp how to set up the filters and opting for the "default allow" set of rules which greatly diminishes the effectiveness of the device. | | | | | | X86 | | | | Generic term for a range of processors from the Intel Corporation starting with the 8088 CPU (Central Processing Unit) and based upon the CISC (Complex Instruction Set Computer) instruction set. This processor was used by IBM in it's first PC (Personal Computer) in 1981. This gave rise to the 8086 and then the 80186, 80286, 80386 and 80486. The "x" denotes that a chip is from that range and the "80" is dropped in popular usage. x86s were used in the Pentium range and even current Intel 64-bit "Core" processors and those from Intel's competitors such as AMD. Since Apple's move over to using x86 processors in 2006, the x86 has a virtual monopoly in desktop and notebook PCs. Processors are referred to as being "x86 compatible" or not. The original x86 instuction set was 16-bit (x86-16), then from the 386 32-bit (x86-32) and currently 64-bit (x86-64). The development of software and operating systems has mirrored this, with most major options - MS-DOS, MS Windows, Mac OS X and Linux for example - all being written for the x86 instruction set. Common processor "brands" using x86 architecture include, in rough chronological order, the following: Intel 8086, Intel 8088, Intel 80186, NEC V20 (introduced from 1978), Intel 80286 (introduced 1982), Intel386, AMD Am386 (introduced 1985), Intel486 (introduced 1989), Pentium, AMD K5, AMD K6 (introduced 1993), Pentium Pro, Pentium II, AMD K6-2, Cyrix 6x86, Pentium III (introduced 1995), Athlon, Athlon XP, Pentium 4, Pentium D (introduced 1999), Pentium M (introduced 2003), Intel Core (introduced 2006), Athlon 64 and Intel Core 2 (introduced 2003/06 respectively). | | | |
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