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95-540: The Ultra Port Architecture ( UPA ) bus was developed by Sun Microsystems as a high-speed graphics card to CPU interconnect, beginning with the Ultra 1 workstation in 1995. This computer hardware article is a stub . You can help Misplaced Pages by expanding it . Sun Microsystems Sun Microsystems, Inc. ( Sun for short) was an American technology company that sold computers , computer components , software , and information technology services and created

190-441: A 1 KB tiny page. ARM uses a two-level page table if using 4 KB and 64 KB pages, or just a one-level page table for 1 MB sections and 16 MB sections. TLB updates are performed automatically by page table walking hardware. PTEs include read/write access permission based on privilege, cacheability information, an NX bit , and a non-secure bit. DEC Alpha processors divide memory into 8 KB , 16 KB , 32 KB , or 64 KB ;

285-426: A 16-bit address that made it too small as memory sizes increased in the 1970s. This was addressed by expanding the physical memory bus to 18-bits, and using an MMU to add two more bits based on other pins on the processor bus to indicate which program was accessing memory. Another use of this same technique, although not referred to as paging but bank switching , was widely used by early 8-bit microprocessors like

380-465: A 20% stake in Sun. UNIX System V Release 4 (SVR4) was jointly developed by AT&T and Sun. Sun used SVR4 as the foundation for Solaris 2.x, which became the successor to SunOS 4.1.x (later retroactively named Solaris 1.x). By the mid-1990s, the ensuing Unix wars had largely subsided, AT&T had sold off their Unix interests, and the relationship between the two companies was significantly reduced. In

475-408: A TLB exception occurs when processing a TLB exception, a double fault TLB exception, it is dispatched to its own exception handler . MIPS32 and MIPS32r2 support 32 bits of virtual address space and up to 36 bits of physical address space. MIPS64 supports up to 64 bits of virtual address space and up to 59 bits of physical address space. The original Sun-1 is a single-board computer built around

570-416: A consistent design philosophy. Sun's first workstation shipped with UniSoft V7 Unix . Later in 1982 Sun began providing SunOS , a customized 4.2BSD Unix, as the operating system for its workstations. SunOS included suntools , an early GUI window system . In the late 1980s, AT&T tapped Sun to help them develop the next release of their branded UNIX, and in 1988 announced they would purchase up to

665-646: A context is 1024 pages or 2 MB. The maximum physical address that can be mapped simultaneously is also 2 MB. The context register is important in a multitasking operating system because it allows the CPU to switch between processes without reloading all the translation state information. The 4-bit context register can switch between 16 sections of the segment map under supervisor control, which allows 16 contexts to be mapped concurrently. Each context has its own virtual address space. Sharing of virtual address space and inter-context communications can be provided by writing

760-462: A contiguous series of fixed-sized blocks. This is similar to the modern demand paging system in that the result is a series of pages, but in these earlier systems the list of pages is fixed in size and normally stored in some form of fast memory like static RAM to improve performance. In this case, the two parts of the address stored by the MMU are known as the segment number and page index . Consider

855-461: A fault on write bit. The MIPS architecture supports one to 64 entries in the TLB. The number of TLB entries is configurable at CPU configuration before synthesis. TLB entries are dual. Each TLB entry maps a virtual page number (VPN2) to either one of two page frame numbers (PFN0 or PFN1), depending on the least significant bit of the virtual address that is not part of the page mask . This bit and

950-442: A fixed set of blocks instead of loading them on demand. The difference between these two approaches is the size of the contiguous block of memory; paged systems break up main memory into a series of equal sized blocks, while segmented systems generally allow for variable sizes. Early memory management systems, often implemented in software, set aside a portion of memory to hold a series of mappings. These consisted of pairs of values,

1045-516: A fixed-size list of pages that divided up memory; this meant that the block size was a function of the number of pages and the installed memory. Another common technique, found mostly on larger machines, was segmented translation, which allowed for variable-size blocks of memory that better mapped onto program requests. This was efficient but did not map as well onto virtual memory. Some early systems, especially 8-bit systems, used very simple MMUs to perform bank switching . Modern MMUs typically divide

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1140-497: A line of x64 systems that support not only Solaris, but also Linux and Microsoft Windows . In January 2007 Sun announced a broad strategic alliance with Intel . Intel endorsed Solaris as a mainstream operating system and as its mission critical Unix for its Xeon processor–based systems, and contributed engineering resources to OpenSolaris . Sun began using the Intel Xeon processor in its x64 server line, starting with

1235-418: A list of page number originally expressed by the program and the actual page number in main memory. When it attempts to access memory, the MMU reads the segment number from the processor's memory bus, finds the corresponding entry for that program in its internal memory, and expresses the mapped version of the value on the memory's bus while the lower bits of the original address are passed through unchanged. Like

1330-713: A net GAAP profit of $ 126 million on revenue of $ 3.337 billion for its fiscal second quarter. Shortly following that news, it was announced that Kohlberg Kravis Roberts (KKR) would invest $ 700 million in the company. Sun had engineering groups in Bangalore , Beijing , Dublin , Grenoble , Hamburg , Prague , St. Petersburg , Tel Aviv , Tokyo , Canberra and Trondheim . In 2007–2008, Sun posted revenue of $ 13.8 billion and had $ 2 billion in cash. First-quarter 2008 losses were $ 1.68 billion; revenue fell 7% to $ 12.99 billion. Sun's stock lost 80% of its value November 2007 to November 2008, reducing

1425-433: A page table entry or other per-page information prohibits access to a particular virtual page, perhaps because no physical random-access memory (RAM) has been allocated to that virtual page. In this case, the MMU signals a page fault to the CPU. The operating system (OS) then handles the situation, perhaps by trying to find a spare frame of RAM and set up the page map to map it to the requested virtual address. If no RAM

1520-682: A primary developer of the Berkeley Software Distribution (BSD), joined soon after and is counted as one of the original founders. The company was the second, after rival Apollo Computer , to specialize in workstations. The name "Sun" is derived from the initials of the Stanford University Network (SUN). Sun was profitable from its first quarter in July 1982. By 1983, Sun was known for producing 68k-based systems with high-quality graphics that were

1615-481: A processor design with 24-bit addressing, like the original Motorola 68000 . In such a system, the MMU splits the virtual address into parts, for instance, the 13 least significant bits for the page index and the remaining 11 most significant bits as the segment number. This results a list of 2048 pages of 8 kB each. In this approach, memory requests result in one or more pages being granted to that program, which may not be contiguous in main memory. The MMU maintains

1710-411: A program refers to a location in a page that is not in physical memory, the MMU will cause an interrupt to the operating system . The OS will then select a lesser-used block in memory, write it to backing storage such as a hard drive if it has been modified since it was read in, read the page from backing storage into that block, and set up the MMU to map the block to the originally requested page so

1805-437: A reputation as one of Microsoft 's most vocal antagonists, Sun entered into a joint relationship with them, resolving various legal entanglements between the two companies and receiving US$ 1.95 billion in settlement payments from them. Sun supported Microsoft Windows on its x64 systems, and announced other collaborative agreements with Microsoft, including plans to support each other's virtualization environments. In 2005,

1900-562: A request, but this is spread out and cannot be allocated. On systems where programs start and stop over time, this can eventually lead to memory being highly fragmented and no large blocks remaining. A number of algorithms were developed to address this problem. Segmenting was widely used on microcomputer platforms of the 1980s. Among the MMUs that used this concept were the Motorola 68451 and Signetics 68905, but many other examples exist. It

1995-785: A set of bits to index the root level of the tree, a set of bits to index the middle level of the tree, a set of bits to index the leaf level of the tree, and remaining bits that pass through to the physical address without modification, indexing a byte within the page. The sizes of the fields are dependent on the page size; all three tree index fields are the same size. The OpenVMS AXP PALcode supports full read and write permission bits for user, supervisor, executive, and kernel modes, and also supports fault on read/write/execute bits are also supported. The DEC OSF/1 PALcode supports full read and write permission bits for user and kernel modes, and also supports fault on read/write/execute bits are also supported. The Windows NT AXP PALcode can either walk

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2090-473: A set of bits to index the root level of the tree, a set of bits to index the top level of the tree, a set of bits to index the leaf level of the tree, and remaining bits that pass through to the physical address without modification, indexing a byte within the page. The sizes of the fields are dependent on the page size. The Windows NT AXP PALcode supports a page being accessible only from kernel mode or being accessible from user and kernel mode, and also supports

2185-427: A single-level page table in a virtual address space or a two-level page table in physical address space. The upper 32 bits of an address are ignored. For a single-level page table, addresses are broken down into a set of bits to index the page table and remaining bits that pass through to the physical address without modification, indexing a byte within the page. For a two-level page table, addresses are borken down into

2280-741: A suite of software products, including the Solaris operating system , developer tools, Web infrastructure software, and identity management applications. Technologies included the Java platform and NFS . In general, Sun was a proponent of open systems, particularly Unix. It was also a major contributor to open-source software , as evidenced by its $ 1 billion purchase, in 2008, of MySQL , an open-source relational database management system . At various times, Sun had manufacturing facilities in several locations worldwide, including Newark, California ; Hillsboro, Oregon ; and Linlithgow, Scotland . However, by

2375-487: A uniform fashion. The MMU is implemented in hardware on the CPU board. The MMU consists of a context register, a segment map and a page map. Virtual addresses from the CPU are translated into intermediate addresses by the segment map, which in turn are translated into physical addresses by the page map. The page size is 2 KB and the segment size is 32 KB which gives 16 pages per segment. Up to 16 contexts can be mapped concurrently. The maximum logical address space for

2470-484: A variety of pricing bases, including per-employee and per-socket. A 2006 report prepared for the EU by UNU-MERIT stated that Sun was the largest corporate contributor to open source movements in the world. According to this report, Sun's open source contributions exceed the combined total of the next five largest commercial contributors. Sun is best known for its Unix systems, which have a reputation for system stability and

2565-470: A very fast memory and thus reduces the need to talk to the slower main memory. In some implementations, they are also responsible for bus arbitration , controlling access to the memory bus among the many parts of the computer that desire access. Prior to VM systems becoming widespread in the 1990s, earlier MMU designs were more varied. Common among these was paged translation, which was similar to modern demand paging in that it used fixed-size blocks, but had

2660-616: Is Solaris 10 1/13. Memory management unit In modern systems, programs generally have addresses that access the theoretical maximum memory of the computer architecture , 32 or 64 bits. The MMU maps the addresses from each program into separate areas in physical memory, which is generally much smaller than the theoretical maximum. This is possible because programs rarely use large amounts of memory at any one time. Most modern operating systems (OS) work in concert with an MMU to provide virtual memory (VM) support. The MMU tracks memory use in fixed-size blocks known as pages , and if

2755-518: Is an SMP capable version of UltraSPARC T2, available in 2 or 4 processor configurations. It was the first CoolThreads CPU with multi-processor capability and it made possible to build standard rack-mounted servers that could simultaneously process up to massive 256 CPU threads in hardware (Sun SPARC Enterprise T5440), which is considered a record in the industry. Since 2010, all further development of Sun machines based on SPARC architecture (including new SPARC T-Series servers, SPARC T3 and T4 chips)

2850-604: Is an increasing need to reduce power and air conditioning demands, much of which comes from the heat generated by CPUs. The T1 was followed in 2007 by the UltraSPARC T2 , which extended the number of threads per core from 4 to 8. Sun has open sourced the design specifications of both the T1 and T2 processors via the OpenSPARC project. In 2006, Sun ventured into the blade server (high density rack-mounted systems) market with

2945-509: Is done as a part of Oracle Corporation hardware division. In the late 1980s, Sun also marketed an Intel 80386 –based machine, the Sun386i ; this was designed to be a hybrid system, running SunOS but at the same time supporting DOS applications. This only remained on the market for a brief time. A follow-up "486i" upgrade was announced but only a few prototype units were ever manufactured. Sun's brief first foray into x86 systems ended in

Ultra Port Architecture - Misplaced Pages Continue

3040-552: Is free, it may be necessary to choose an existing page (known as a victim ), using some replacement algorithm , and save it to disk (a process called paging ). With some MMUs, there can also be a shortage of PTEs, in which case the OS will have to free one for the new mapping. The MMU may also generate illegal access error conditions or invalid page faults upon illegal or non-existing memory accesses, respectively, leading to segmentation fault or bus error conditions when handled by

3135-446: Is one of the benefits of paging . However, paged mapping causes another problem, internal fragmentation . This occurs when a program requests a block of memory that does not cleanly map into a page, for instance, if a program requests a 1 KB buffer to perform file work. In this case, the request results in an entire page being set aside even though only 1 KB of the page will ever be used; if pages are larger than 1 KB,

3230-399: Is very small. An OS may treat multiple pages as if they were a single larger page. For example, Linux on VAX groups eight pages together. Thus, the system is viewed as having 4 KB pages. The VAX divides memory into four fixed-purpose regions, each 1 GB in size. They are: Page tables are big linear arrays. Normally, this would be very wasteful when addresses are used at both ends of

3325-515: The Java programming language , the Solaris operating system , ZFS , the Network File System (NFS), and SPARC microprocessors . Sun contributed significantly to the evolution of several key computing technologies, among them Unix , RISC processors , thin client computing, and virtualized computing . Notable Sun acquisitions include Cray Business Systems Division , Storagetek , and Innotek GmbH , creators of VirtualBox . Sun

3420-593: The MOS 6502 . For instance, the Atari MMU would express additional bits on the address bus to select among several banks of DRAM memory based on which of the chips was currently active, normally the CPU or ANTIC . This was used to expand the available memory on the Atari 130XE to 128 kB. The Commodore 128 used a similar approach. Most modern systems divide memory into pages that are 4–64 KB in size, often with

3515-495: The Motorola 68000 microprocessor and introduced in 1982. It includes the original Sun 1 memory management unit that provides address translation, memory protection, memory sharing and memory allocation for multiple processes running on the CPU. All access of the CPU to private on-board RAM, external Multibus memory, on-board I/O and the Multibus I/O runs through the MMU, where address translation and protection are done in

3610-769: The SUN workstation for the Stanford University Network communications project as a personal CAD workstation . 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. He built the first examples from spare parts obtained from Stanford's Department of Computer Science and Silicon Valley supply houses. On February 24, 1982, Scott McNealy , Andy Bechtolsheim , and Vinod Khosla , all Stanford graduate students, founded Sun Microsystems . Bill Joy of Berkeley,

3705-646: The Sun Blade (distinct from the Sun Blade workstation). In April 2007, Sun released the SPARC Enterprise server products, jointly designed by Sun and Fujitsu and based on Fujitsu SPARC64 VI and later processors. The M-class SPARC Enterprise systems include high-end reliability and availability features. Later T-series servers have also been badged SPARC Enterprise rather than Sun Fire. In April 2008, Sun released servers with UltraSPARC T2 Plus, which

3800-556: The Sun-1 through Sun-3 computer series. The Sun-1 employed a 68000 CPU, the Sun-2 series, a 68010 . The Sun-3 series was based on the 68020 , with the later Sun-3x using the 68030 . In 1987, the company began using SPARC , a RISC processor architecture of its own design, in its computer systems, starting with the Sun-4 line. SPARC was initially a 32-bit architecture (SPARC V7) until

3895-592: The Zilog Z8000 family of processors. Later microprocessors (such as the Motorola 68030 and the Zilog Z280 ) placed the MMU together with the CPU on the same integrated circuit, as did the Intel 80286 and later x86 microprocessors. While this article concentrates on modern MMUs, commonly based on demand paging, early systems used base and bounds addressing that further developed into segmentation , or used

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3990-494: The base and limit , although many other terms have been used. When the operating system requested memory to load a program, or a program requested more memory to hold data from a file for instance, it would call the memory handling library . This examined the mappings to look for an area in main memory large enough to hold the request. If such a block was found, a new entry was entered into the table. From then on, when that program accessed memory, all of its addresses were offset by

4085-582: The dot-com bubble , Sun began making more money, with its stock rising as high as $ 250 per share. It also began spending much more, hiring workers and building itself out. Some of this was because of genuine demand, but much was from web start-up companies anticipating business that would never happen. In 2000, the bubble burst. Sales in Sun's important hardware division went into free-fall as customers closed shop and auctioned high-end servers. Several quarters of steep losses led to executive departures, rounds of layoffs, and other cost cutting. In December 2001,

4180-457: The 1980s. This problem can be reduced by making the pages larger, say 64 kB instead of 8. Now the page index uses 16 bits and the resulting page table is 64 kB, which is more tractable. Moving to a larger page size leads to the second problem, increased internal fragmentation. A program that generates a series of requests for small block will be assigned large blocks and thereby waste large amounts of memory. The paged translation approach

4275-558: The CPU, with four processor registers holding base values accessed directly by the program. These mapped only the upper 4 bits of the 20-bit address, and there was no equivalent of a limit, which was simply the lower 16-bits of the address and thus a fixed 64 kB. Later entries in the x86 architecture series used different approaches. Some systems, such as the GE 645 and its successors, used both segmentation and paging. The table of segments, instead of containing per-segment entries giving

4370-797: The Japanese company's processor chips in mid-range and high-end Sun servers. These servers were announced on April 17, 2007, as the M-Series, part of the SPARC Enterprise series. In February 2005, Sun announced the Sun Grid , a grid computing deployment on which it offered utility computing services priced at US$ 1 per CPU/hour for processing and per GB/month for storage. This offering built upon an existing 3,000-CPU server farm used for internal R&D for over 10 years, which Sun marketed as being able to achieve 97% utilization. In August 2005,

4465-532: The LX50, based in part on previous Cobalt system expertise. This was also Sun's first system announced to support Linux as well as Solaris. In 2003, Sun announced a strategic alliance with AMD to produce x86/x64 servers based on AMD's Opteron processor; this was followed shortly by Sun's acquisition of Kealia, a startup founded by original Sun founder Andy Bechtolsheim , which had been focusing on high-performance AMD-based servers. The following year, Sun launched

4560-464: The MMU when trapping into OS code. The IBM System/360 Model 67 , which was introduced August, 1965, included an MMU called a dynamic address translation (DAT) box. It has the unusual feature of storing accessed and dirty bits outside of the page table (along with the four bit protection key for all S/360 processors). They refer to physical memory rather than virtual memory, and are accessed by special-purpose instructions. This reduces overhead for

4655-525: The Newark campus was put on the market. In 2004, Sun canceled two major processor projects which emphasized high instruction-level parallelism and operating frequency. Instead, the company chose to concentrate on processors optimized for multi-threading and multiprocessing , such as the UltraSPARC T1 processor (codenamed "Niagara"). The company also announced a collaboration with Fujitsu to use

4750-520: The OS, which would otherwise need to propagate accessed and dirty bits from the page tables to a more physically oriented data structure. This makes OS-level virtualization , later called paravirtualization , easier. Starting in August, 1972, the IBM System/370 has a similar MMU, although it initially supported only a 24-bit virtual address space rather than the 32-bit virtual address space of

4845-738: The Opteron-based Sun Fire V20z and V40z servers, and the Sun Java Workstation W1100z and W2100z workstations. In September 2005 Sun unveiled a new range of Opteron-based servers: the Sun Fire X2100, X4100 and X4200 servers. These were designed from scratch by a team led by Bechtolsheim to address heat and power consumption issues commonly faced in data centers. In July 2006, the Sun Fire X4500 and X4600 systems were introduced, extending

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4940-544: The Sun Blade X6250 server module introduced in June 2007. In May 2008 AMD announced its Operating System Research Center (OSRC) was expanding its focus to include optimization to Sun's OpenSolaris and xVM virtualization products for AMD processors. Although Sun was initially known as a hardware company, its software history began with its founding in 1982; co-founder Bill Joy was one of the leading Unix developers of

5035-532: The System/360 Model 67. It also stores the accessed and dirty bits outside the page table. In early 1983, the System/370-XA architecture expanded the virtual address space to 31 bits, and in 2000, the 64-bit z/Architecture was introduced, with the address space expanded to 64 bits; those continue to store the accessed and dirty bits outside the page table. VAX pages are 512 bytes, which

5130-454: The accessed bit if they are to operate efficiently. Typically, the OS will periodically unmap pages so that page-not-present faults can be used to let the OS set an accessed bit. ARM architecture -based application processors implement an MMU defined by ARM's virtual memory system architecture. The current architecture defines PTEs for describing 4 KB and 64 KB pages, 1 MB sections and 16 MB super-sections; legacy versions also defined

5225-596: The aim of building network appliances (single function computers meant for consumers). Sun also marketed a Network Computer (a term popularized and eventually trademarked by Oracle ); the JavaStation was a diskless system designed to run Java applications. Although none of these business initiatives were particularly successful, the Cobalt purchase gave Sun a toehold for its return to the x86 hardware market. In 2002, Sun introduced its first general purpose x86 system,

5320-576: The amounts indicated when the acquisition closed. For the first decade of Sun's history, the company positioned its products as technical workstations , competing successfully as a low-cost vendor during the Workstation Wars of the 1980s. It then shifted its hardware product line to emphasize servers and storage. High-level telecom control systems such as Operational Support Systems service predominantly used Sun equipment. Sun originally used Motorola 68000 family central processing units for

5415-411: The base value. When the program is done with the memory it requested and releases, or the program exits, the entries associated with it are released. This style of access, over time, became common in the mainframe market and was known as segmented translation , although a variety of terms are used here as well. This style has the advantage of simplicity; the memory blocks are continuous and thus only

5510-402: The capability to use so-called huge pages of 2 MB or 1 GB in size (often both variants are possible). Page translations are cached in a translation lookaside buffer (TLB). Some systems, mainly older RISC designs, trap into the OS when a page translation is not found in the TLB. Most systems use a hardware-based tree walker. Most systems allow the MMU to be disabled, but some disable

5605-403: The company released Solaris 10. The new version included a large number of enhancements to the operating system, as well as very novel features, previously unseen in the industry. Solaris 10 update releases continued through the next 8 years, the last release from Sun Microsystems being Solaris 10 10/09. The following updates were released by Oracle under the new license agreement; the final release

5700-418: The company's current strategy. Sun's logo, which features four interleaved copies of the word sun in the form of a rotationally symmetric ambigram , was designed by professor Vaughan Pratt , also of Stanford. The initial version of the logo was orange and had the sides oriented horizontally and vertically, but it was subsequently rotated to stand on one corner and re-colored purple, and later blue. During

5795-472: The company's market value to $ 3 billion. With falling sales to large corporate clients, Sun announced plans to lay off 5,000 to 6,000 workers, or 15–18% of its work force. It expected to save $ 700 million to $ 800 million a year as a result of the moves, while also taking up to $ 600 million in charges. As of May 11, 2009, the following shareholders held over 100,000 common shares of Sun and at $ 9.50 per share offered by Oracle, they received

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5890-738: The early 1990s, Brian P. Dougherty , founder of Berkeley Softworks (which would go on to be re-incorporated as the GeoWorks Corporation ) accused the Java development team at Sun for studying GeoWorks's PC/GEOS operating system and incorporating features of PC/GEOS into their Unix-based operating system. Brian claimed that the object-oriented and flexible UI of PC/GEOS was "to this day the most sophisticated UI technology ever built into an OS". From 1992 Sun also sold Interactive Unix , an operating system it acquired when it bought Interactive Systems Corporation from Eastman Kodak Company. This

5985-402: The early 1990s, as it decided to concentrate on SPARC and retire the last Motorola systems and 386i products, a move dubbed by McNealy as "all the wood behind one arrowhead". Even so, Sun kept its hand in the x86 world, as a release of Solaris for PC compatibles began shipping in 1993. In 1997, Sun acquired Diba, Inc., followed later by the acquisition of Cobalt Networks in 2000, with

6080-441: The first commercial use of this grid was announced for financial risk simulations which were later launched as its first software as a service product. In January 2005, Sun reported a net profit of $ 19 million for fiscal 2005 second quarter, for the first time in three years. This was followed by net loss of $ 9 million on GAAP basis for the third quarter 2005, as reported on April 14, 2005. In January 2007, Sun reported

6175-431: The four-processor SPARCserver 600MP. This was followed by the 8-processor SPARCserver 1000 and 20-processor SPARCcenter 2000, which were based on work done in conjunction with Xerox PARC . In 1995 the company introduced Sun Ultra series machines that were equipped with the first 64-bit implementation of SPARC processors ( UltraSPARC ). In the late 1990s the transformation of product line in favor of large 64-bit SMP systems

6270-627: The introduction of the SPARC V9 architecture in 1995, which added 64-bit extensions. Sun developed several generations of SPARC-based computer systems, including the SPARCstation , Ultra , and Sun Blade series of workstations, and the SPARCserver, Netra , Enterprise , and Sun Fire line of servers. In the early 1990s the company began to extend its product line to include large-scale symmetric multiprocessing servers, starting with

6365-411: The main memory every time a virtual address is mapped. Other MMUs may have a private array of memory, registers, or static RAM that holds a set of mapping information. The virtual page number may be directly used as an index into the page table or other mapping information, or it may be further divided, with bits at a given level used as an index into a table of lower-level tables into which bits at

6460-526: The most powerful, enterprise class high-end CC-NUMA servers developed by Sun, such as the Sun Fire E15K and the Sun Fire E25K . In November 2005, Sun launched the UltraSPARC T1 , notable for its ability to concurrently run 32 threads of execution on 8 processor cores. Its intent was to drive more efficient use of CPU resources, which is of particular importance in data centers , where there

6555-632: The new UltraSPARC CPUs based on the SPARC V9 architecture. Within the next four years, the successors Solaris 8 and Solaris 9 were released in 2000 and 2002 respectively. Following several years of difficult competition and loss of server market share to competitors' Linux-based systems, Sun began to include Linux as part of its strategy in 2002. Sun supported both Red Hat Enterprise Linux and SUSE Linux Enterprise Server on its x64 systems; companies such as Canonical Ltd. , Wind River Systems and MontaVista also supported their versions of Linux on Sun's SPARC-based systems. In 2004, after having cultivated

6650-560: The next level down are used as an index, with two or more levels of indexing. The physical page number is combined with the page offset to give the complete physical address. A page table entry or other per-page information may also include information about whether the page has been written to (the dirty bit ), when it was last used (the accessed bit , for a least recently used (LRU) page replacement algorithm ), what kind of processes ( user mode or supervisor mode ) may read and write it, and whether it should be cached . Sometimes,

6745-464: The only computers other than DEC 's VAX to run 4.2BSD . It licensed the computer design to other manufacturers, which typically used it to build Multibus -based systems running Unix from UniSoft . Sun's initial public offering was in 1986 under the stock symbol SUNW , for Sun Workstations (later Sun Worldwide ). The symbol was changed in 2007 to JAVA ; Sun stated that the brand awareness associated with its Java platform better represented

6840-432: The operating system. In some cases, a page fault may indicate a software bug , which can be prevented by using memory protection as one of key benefits of an MMU: an operating system can use it to protect against errant programs by disallowing access to memory that a particular program should not have access to. Typically, an operating system assigns each program its own virtual address space. A paged MMU also mitigates

6935-455: The page mask bits are not stored in the VPN2. Each TLB entry has its own page size, which can be any value from 1 KB to 256 MB in multiples of four. Each PFN in a TLB entry has a caching attribute, a dirty and a valid status bit. A VPN2 has a global status bit and an OS assigned ID which participates in the virtual address TLB entry match, if the global status bit is set to zero. A PFN stores

7030-400: The page size is dependent on the processor. pages. After a TLB miss, low-level firmware machine code (here called PALcode ) walks a page table. The OpenVMS AXP PALcode and DEC OSF/1 PALcode walk a three-level tree-structured page table. Addresses are broken down into an unused set of bits (containing the same value as the uppermost bit of the index into the root level of the tree),

7125-401: The physical address without the page mask bits. A TLB refill exception is generated when there are no entries in the TLB that match the mapped virtual address. A TLB invalid exception is generated when there is a match but the entry is marked invalid. A TLB modified exception is generated when a store instruction references a mapped address and the matching entry's dirty status is not set. If

7220-414: The physical base address and length of the segment, contains entries giving the physical base address of a page table for the segment, in addition to the length of the segment. Physical memory is divided into fixed-size pages, and the same techniques used for purely page-based demand paging are used for segment-and-page-based demand paging. Another approach to memory handling is to break up main memory into

7315-467: The possible range, but the page tables for P0 and P1 space are stored in the paged S0 space. Thus, there is effectively a two-level tree , allowing applications to have sparse memory layout without wasting a lot of space on unused page table entries. Unlike page table entries in most MMUs, page table entries in the VAX MMU lack an accessed bit . OSes which implement paging must find some way to emulate

7410-416: The problem of external fragmentation of memory. After blocks of memory have been allocated and freed, the free memory may become fragmented (discontinuous) so that the largest contiguous block of free memory may be much smaller than the total amount. With virtual memory, a contiguous range of virtual addresses can be mapped to several non-contiguous blocks of physical memory; this non-contiguous allocation

7505-432: The program can use it. This is known as demand paging . Modern MMUs generally perform additional memory-related tasks as well. Memory protection blocks attempts by a program to access memory it has not previously requested, which prevents a misbehaving program from using up all memory or malicious code from reading data from another program. They also often manage a processor cache , which stores recently accessed data in

7600-614: The remainder of the page is wasted. If many small allocations of this sort are made, memory can be used up even though much of it remains empty. In some early microprocessor designs, memory management was performed by a separate integrated circuit such as the VLSI Technology VI475 (1986), the Motorola 68851 (1984) used with the Motorola 68020 CPU in the Macintosh II , or the Z8010 and Z8015 (1985) used with

7695-443: The same values in to the segment or page maps of different contexts. Additional contexts can be handled by treating the segment map as a context cache and replacing out-of-date contexts on a least-recently used basis. The context register makes no distinction between user and supervisor states. Interrupts and traps do not switch contexts, which requires that all valid interrupt vectors always be mapped in page 0 of context, as well as

7790-518: The segmented case, programs see its memory as a single contiguous block. There are two disadvantages to this approach. The first is that as the virtual address space expands, the amount of memory needed to hold the mapping increases as well. For instance, in the 68020 the addresses are 32-bits wide, meaning the segment number for the same 8 kB page size is now the upper 19 bits and the mapping table expands to 512 kB in size, far beyond what could be implemented in hardware for reasonable cost in

7885-402: The stock fell to the 1998, pre-bubble level of about $ 100. It continued to fall, faster than many other technology companies. A year later, it had reached below $ 10 (a tenth of what it was in 1990), but it eventually bounced back to $ 20. In mid-2004, Sun closed their Newark, California , factory and consolidated all manufacturing to Hillsboro, Oregon and Linlithgow, Scotland. In 2006, the rest of

7980-547: The time the company was acquired by Oracle Corporation , it had outsourced most manufacturing responsibilities. On April 20, 2009, it was announced that Oracle would acquire Sun for US$ 7.4 billion. The deal was completed on January 27, 2010. 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. Bechtolsheim originally designed

8075-736: The time, having contributed the vi editor, the C shell , and significant work developing TCP/IP and the BSD Unix OS. Sun later developed software such as the Java programming language and acquired software such as StarOffice , VirtualBox and MySQL . In February 1991, the company established SunSoft, Inc., a wholly owned division of Sun dedicated to the development of operating systems and application software. Sun used community-based and open-source licensing of its major technologies, and for its support of its products with other open source technologies. GNOME -based desktop software called Java Desktop System (originally code-named "Madhatter")

8170-482: The two values, base and limit, need to be stored. Each entry corresponds to a block of memory used by a single program, and the translation is invisible to the program, which sees main memory starting at address zero and extending to some fixed value. The disadvantage of this approach is that it leads to an effect known as external fragmentation . This occurs when memory allocations are released but are non-contiguous. In this case, enough memory may be available to handle

8265-492: The valid supervisor stack. The Sun-2 workstations are similar; they are built around the Motorola 68010 microprocessor and have a similar memory management unit, with 2 KB pages and 32 KB segments. The context register has a 3-bit system context used in supervisor state and a 3-bit user context used in user state. The Sun-3 workstations, except for the Sun-3/80, Sun-3/460, Sun-3/470, and Sun-3/480, are built around

8360-407: The virtual address space (the range of addresses used by the processor) into pages , each having a size which is a power of 2, usually a few kilobytes , but they may be much larger. Programs reference memory using the natural address size of the machine, typically 32 or 64-bits in modern systems. The bottom bits of the address (the offset within a page) are left unchanged. The upper address bits are

8455-423: The virtual page numbers. Most MMUs use an in-memory table of items called a page table , containing one page table entry (PTE) per virtual page, to map virtual page numbers to physical page numbers in main memory. Multi-level page tables are often used to reduce the size of the page table. An associative cache of PTEs is called a translation lookaside buffer (TLB) and is used to avoid the necessity of accessing

8550-519: Was a popular Unix variant for the PC platform and a major competitor to market leader SCO UNIX . Sun's focus on Interactive Unix diminished in favor of Solaris on both SPARC and x86 systems; it was dropped as a product in 2001. Sun dropped the Solaris 2.x version numbering scheme after the Solaris 2.6 release (1997); the following version was branded Solaris 7. This was the first 64-bit release, intended for

8645-635: Was accelerated by the acquisition of Cray Business Systems Division from Silicon Graphics. Their 32-bit, 64-processor Cray Superserver 6400 , related to the SPARCcenter, led to the 64-bit Sun Enterprise 10000 high-end server (otherwise known as Starfire or E10K). In September 2004, Sun made available systems with UltraSPARC IV which was the first multi-core SPARC processor. It was followed by UltraSPARC IV+ in September 2005 and its revisions with higher clock speeds in 2007. These CPUs were used in

8740-581: Was also supported in software implementations; one example is Apple's MultiFinder , released in 1987 for the Macintosh platform. Each program was allocated an amount of memory that was pre-selected in the Finder and translation from virtual to physical was accomplished within the programs using handles . A more common example is the Intel 8088 used in the IBM PC . This implemented a very simple MMU inside

8835-523: Was distributed for the Solaris operating system, and at one point for Linux. Sun supported its Java Enterprise System (a middleware stack) on Linux. It released the source code for Solaris under the open-source Common Development and Distribution License , via the OpenSolaris community. Sun's positioning includes a commitment to indemnify users of some software from intellectual property disputes concerning that software. It offers support services on

8930-581: Was founded on February 24, 1982. At its height, the Sun headquarters were in Santa Clara, California (part of Silicon Valley ), on the former west campus of the Agnews Developmental Center . Sun products included computer servers and workstations built on its own RISC -based SPARC processor architecture , as well as on x86 -based AMD Opteron and Intel Xeon processors. Sun also developed its own storage systems and

9025-527: Was widely used by microprocessor MMUs in the 1970s and early 80s, including the Signetics 68905 (which could operate in either mode). Both Signetics and Philips produced a version of the 68000 that combined the 68905 on the same physical chip, the 68070. Another use of this technique is to expand the size of the physical address when the virtual address is too small. For instance, the PDP-11 originally had

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