Thursday, August 28, 2008

Random access memory

Random access memory (usually known by its acronym, RAM) is a type of computer data storage. Today it takes the form of integrated circuits that allow the stored data to be accessed in any order, i.e. at random. The word random thus refers to the fact that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data.This contrasts with storage mechanisms such as tapes, magnetic discs and optical discs, which rely on the physical movement of the recording medium or a reading head. In these devices, the movement takes longer than the data transfer, and the retrieval time varies depending on the physical location of the next item.

An early type of widespread writable random access memory was the magnetic core memory, developed in 1949-1951, and subsequently used in most computers up until the development of the static and dynamic integrated RAM circuits in the late 1960s and early 1970s. Before this, computers used relays, delay lines or various kinds of vacuum tube arrangements to implement "main" memory functions (i.e. hundreds or thousands of bits), some of which were random access, some not. Latches built out of vacuum tube triodes, and later, out of discrete transistors, were used for smaller and faster memories such as registers and (random access) register banks. Prior to the development of integrated ROM circuits, permanent (or read-only) random access memory was often constructed using semiconductor diode matrixes driven by address decoders.

Types of RAM:
RAM generally store a bit of data in either the state of a flip-flop, as in SRAM (static RAM), or as a charge in a capacitor (or transistor gate), as in DRAM (dynamic RAM), EPROM, EEPROM and Flash. Some types have circuitry to detect and/or correct random faults called memory errors in the stored data, using parity bits or error correction codes. RAM of the read-only type, ROM, instead uses a metal mask to permanently enable/disable selected transistors, instead of storing a charge in them.

Monday, August 25, 2008


iPOD is a popular brand of portable media players designed and marketed by Apple Inc. and launched on October 23, 2001. As of 2008, the current product line-up includes the hard drive-based iPod Classic, the touchscreen iPod Touch, the video-capable iPod Nano, the screenless iPod Shuffle and the iPhone. Former products include the compact iPod Mini and the spin-off iPod Photo (since re-integrated into the main iPod Classic line). iPod Classic models store media on an internal hard drive, while all other models use flash memory to enable their smaller size (the discontinued mini used a Microdrive miniature hard drive). As with many other digital music players, iPods, excluding the iPod Touch, can also serve as external data storage devices. Storage capacity varies by model.Apple's iTunes software can be used to transfer music to the devices from computers using certain versions of Apple Macintosh and Microsoft Windows operating systems. users who choose not to use Apple's software or whose computers cannot run iTunes software, several open source alternatives to iTunes are also available. iTunes and its alternatives may also transfer photos, videos, games, contact information, e-mail settings, Web bookmarks, and calendars to iPod models supporting those features. Apple focused its development on the iPod line's unique user interface and its ease of use, rather than on technical capability. As of September 2007, more than 150 million iPods had been sold worldwide, making it the best-selling digital audio player series in history.


The iPod line can play several audio file formats including MP3, AAC/M4A, Protected AAC, AIFF, WAV, Audible audiobook, and Apple Lossless. The iPod Photo introduced the ability to display JPEG, BMP, GIF, TIFF, and PNG image file formats. Fifth and sixth generation iPod Classics, as well as third generation iPod Nanos, can additionally play MPEG-4 (H.264/MPEG-4 AVC) and QuickTime video formats, with restrictions on video dimensions, encoding techniques and data-rates. Originally, iPod software only worked with Mac OS; iPod software for Microsoft Windows was launched with the second generation model. Unlike most other media players, Apple does not support Microsoft's WMA audio format — but a converter for WMA files without Digital Rights Management (DRM) is provided with the Windows version of iTunes. MIDI files also cannot be played, but can be converted to audio files using the "Advanced" menu in iTunes. Alternative open-source audio formats, such as Ogg Vorbis and FLAC, are not supported without installing custom firmware onto an iPod .
During installation, an iPod is associated with one host computer. Each time an iPod connects to its host computer, iTunes can synchronize entire music libraries or music playlists either automatically or manually. Song ratings can be set on an iPod and synchronized later to the iTunes library, and vice versa. A user can access, play, and add music on a second computer if an iPod is set to manual and not automatic sync, but anything added or edited will be reversed upon connecting and syncing with the main computer and its library. If a user wishes to automatically sync music with another computer, an iPod's library will be entirely wiped and replaced with the other computer's library.

Thursday, August 7, 2008

Sun Microsystems

Sun Microsystems is a multinational vendor of computers, computer components, computer software, and information technology services, founded on 24 February 1982.[4] The company is headquartered in Santa Clara, California (part of Silicon Valley), on the former west campus of the Agnews Developmental Center.

Products include computer servers and workstations based on its own SPARC processors as well as AMD's Opteron and Intel's Xeon processors; storage systems; and, a suite of software products including the Solaris Operating System, developer tools, Web infrastructure software, and identity management applications. Other technologies of note include the Java platform and NFS.

Sun is a proponent of open systems in general and UNIX in particular and a major contributor of open source software.[5]

Sun's manufacturing facilities are located in Hillsboro, Oregon and Linlithgow, Scotland.


The initial design for what became Sun's first Unix workstation, the Sun 1, was conceived by Andy Bechtolsheim when he was a graduate student at Stanford University in Palo Alto, California. He originally designed the SUN workstation for the Stanford University Network communications project as a personal CAD workstation. It was designed as a 3M computer: 1 MIPS, 1 Megabyte and 1 Megapixel. It was designed around the Motorola 68000 processor with an advanced Memory management unit (MMU) to support the Unix operating system with virtual memory support[6], He built the first ones from spare parts obtained from Stanford's Department of Computer Science and Silicon Valley supply houses.[7]

On February 12, 1982 Vinod Khosla, Andy Bechtolsheim, and Scott McNealy, all Stanford graduate students, founded Sun Microsystems. Bill Joy of Berkeley (a primary developer of BSD), joined soon after and is counted as one of the original founders[8]. The Sun name is derived from the initials of the Stanford University Network. Sun was profitable from its first quarter in July 1982.

Sun's initial public offering was in 1986 under the stock symbol SUNW, for Sun Workstations (later Sun Worldwide).[9][10] The symbol was changed in 2007 to JAVA; Sun stated that the brand awareness associated with its Java platform better represented the company's current strategy.[11]

Sun's logo, which features four interleaved copies of the word sun, was designed by professor Vaughan Pratt, also of Stanford University. The initial version of the logo had the sides oriented horizontally and vertically, but it was subsequently redesigned so as to appear to stand on one corner.

The first Sun workstations ran a Version 7 Unix System port by UniSoft on 68000 processor-based machines.

The "Bubble" and its aftermath

During the dot-com bubble, Sun experienced dramatic growth in revenue, profits, share price, and expenses. Some part of this was due to genuine expansion of demand for web-serving cycles, but another part was synthetic, fueled by venture capital-funded startups building out large, expensive Sun-centric server presences in the expectation of high traffic levels that never materialized. The share price in particular increased to a level that even the company's executives were hard-pressed to defend. In response to this business growth, Sun expanded aggressively in all areas: head-count, infrastructure, and office space.

The bursting of the bubble in 2001 was the start of a period of poor business performance for Sun.[12] Sales dropped as the growth of online business failed to meet predictions. As online businesses closed and their assets were auctioned off, a large amount of high-end Sun hardware was available very cheaply. Much like Apple, Sun relied a great deal on hardware sales.

Multiple quarters of substantial losses and declining revenues have led to repeated rounds of layoffs,[13][14][15] executive departures, and expense-reduction efforts. In December of 2001 the share price dropped to the 1998 pre-bubble level of about one hundred dollars or so and then kept going, a rapid fall even by the standards of the high tech sector at that time. The stock dipped below 10 dollars a year later, one-tenth of its 1990 value, then quickly bounced back to 20, where it has hovered ever since. In mid-2004, Sun ceased manufacturing operations at their Newark, California facility and consolidated all of the company's US-based manufacturing operations to their Hillsboro, Oregon facility, as part of continued cost-reduction efforts.[16] In 2006 Sun closed the Newark campus completely and moved 2,300 staff to its other campuses in the area.[17]

Many companies (like E-Trade and Google) chose to build Web applications based on large numbers of the less expensive PC-class x86-architecture servers running Linux, rather than a smaller number of high-end Sun servers. They reported benefits including substantially lower expenses (both acquisition and maintenance) and greater flexibility based on the use of open-source software. That trend is slowing and may be reversing,[citation needed] given (1) the throughput and efficiency of Sun's new horizontally-scaled systems (see below) and (2) the fact that both Sun's flagship Solaris operating system and its UltraSPARC T1 processor are now fully open-source.

Higher level telecoms control systems such as NMAS and OSS service predominantly use Sun equipment. This use is due mainly to the company basing its products around a mature and very stable version of the Unix operating system and the support service that Sun provides.