Misplaced Pages

#670329

61-535: The 68010 and 68012 are completely user-mode compatible with the 68000, except that the MOVE from SR instruction traps in user mode, so that, to support user-mode code using that instruction, a supervisor-mode trap handler must simulate the instruction and continue the user-mode code after that instruction. This was done so that the 68010 and 68012 would meet the Popek and Goldberg virtualization requirements , specifically that

122-468: A high-level programming language (compared to the low-level ISA abstraction of the system VM). Process VMs are implemented using an interpreter ; performance comparable to compiled programming languages can be achieved by the use of just-in-time compilation . This type of VM has become popular with the Java programming language , which is implemented using the Java virtual machine . Other examples include

183-683: A virtual machine ( VM ) is the virtualization or emulation of a computer system . Virtual machines are based on computer architectures and provide the functionality of a physical computer. Their implementations may involve specialized hardware, software, or a combination of the two. Virtual machines differ and are organized by their function, shown here: Some virtual machine emulators, such as QEMU and video game console emulators , are designed to also emulate (or "virtually imitate") different system architectures, thus allowing execution of software applications and operating systems written for another CPU or architecture. OS-level virtualization allows

244-461: A VMM it is sufficient that all instructions that could affect the correct functioning of the VMM (sensitive instructions) always trap and pass control to the VMM. This guarantees the resource control property. Non-privileged instructions must instead be executed natively (i.e., efficiently). The holding of the equivalence property also follows. This theorem also provides a simple technique for implementing

305-438: A VMM, called trap-and-emulate virtualization , more recently called classic virtualization : because all sensitive instructions behave nicely, all the VMM has to do is trap and emulate every one of the sensitive instructions. A related problem is that of deriving sufficient conditions for recursive virtualization, that is, the conditions under which a VMM that can run on a copy of itself can be built. Popek and Goldberg present

366-414: A classification of some instructions of an ISA into 3 different groups: The main result of Popek and Goldberg's analysis can then be expressed as follows. Theorem 1 . For any conventional third-generation computer , an effective VMM may be constructed if the set of sensitive instructions for that computer is a subset of the set of privileged instructions. Intuitively, the theorem states that to build

427-416: A computer architecture supports efficient virtualization and provide guidelines for the design of virtualized computer architectures. System virtual machines are capable of virtualizing a full set of hardware resources, including a processor (or processors), memory and storage resources and peripheral devices. A virtual machine monitor (VMM, also called hypervisor ) is the piece of software that provides

488-478: A nested guest virtual machine does not need to be homogeneous with its host virtual machine; for example, application virtualization can be deployed within a virtual machine created by using hardware virtualization . Nested virtualization becomes more necessary as widespread operating systems gain built-in hypervisor functionality, which in a virtualized environment can be used only if the surrounding hypervisor supports nested virtualization; for example, Windows 7

549-401: A new OS could run as guest and not be aware. A new unprivileged MOVE from CCR instruction was added to compensate for the penalty of trapping user-mode MOVE from SR. The 68010 and 68012 can recover from bus faults, and continue the faulting instruction, allowing them to implement virtual memory . This means that the exception stack frame is different. A 32-bit Vector Base Register (VBR) holds

610-431: A normal application inside a host OS and supports a single process. It is created when that process is started and destroyed when it exits. Its purpose is to provide a platform -independent programming environment that abstracts away details of the underlying hardware or operating system and allows a program to execute in the same way on any platform. A process VM provides a high-level abstraction – that of

671-673: A popular approach to implementing early microcomputer software, including Tiny BASIC and adventure games, from one-off implementations such as Pyramid 2000 to a general-purpose engine like Infocom 's z-machine , which Graham Nelson argues is "possibly the most portable virtual machine ever created". Significant advances occurred in the implementation of Smalltalk -80, particularly the Deutsch/Schiffmann implementation which pushed just-in-time (JIT) compilation forward as an implementation approach that uses process virtual machine. Later notable Smalltalk VMs were VisualWorks ,

SECTION 10

#1732790685671

732-447: A processor that operates in either system or user mode, and has access to linear, uniformly addressable memory. It is assumed that a subset of the instruction set is available only when in system mode and that memory is addressed relative to a relocation register. I/O and interrupts are not modelled. To derive their virtualization theorems, which give sufficient (but not necessary) conditions for virtualization, Popek and Goldberg introduce

793-401: A set of conditions sufficient for a computer architecture to support system virtualization efficiently. They were introduced by Gerald J. Popek and Robert P. Goldberg in their 1974 article "Formal Requirements for Virtualizable Third Generation Architectures". Even though the requirements are derived under simplifying assumptions, they still represent a convenient way of determining whether

854-451: A specific programming language, but are embedded in an existing language; typically such a system provides bindings for several languages (e.g., C and Fortran ). Examples are Parallel Virtual Machine (PVM) and Message Passing Interface (MPI). Both system virtual machines and process virtual machines date to the 1960s and remain areas of active development. System virtual machines grew out of time-sharing , as notably implemented in

915-607: A system virtual machine can be considered a generalization of the concept of virtual memory that historically preceded it. IBM's CP/CMS , the first systems to allow full virtualization , implemented time sharing by providing each user with a single-user operating system, the Conversational Monitor System (CMS). Unlike virtual memory, a system virtual machine entitled the user to write privileged instructions in their code. This approach had certain advantages, such as adding input/output devices not allowed by

976-861: A theorem with different sufficiency conditions. Theorem 3 . A hybrid VMM may be constructed for any third generation machine in which the set of user sensitive instructions are a subset of the set of privileged instructions: The conditions for ISA virtualization expressed in Theorem 1 may be relaxed at the expense of the efficiency property. VMMs for non-virtualizable ISAs (in the Popek and Goldberg's sense) have routinely been built. The virtualization of such architectures requires correct handling of critical instructions , i.e., sensitive but unprivileged instructions. One approach, known as patching , adopts techniques commonly used in dynamic recompilation : critical instructions are discovered at run-time and replaced with

1037-402: A trap into the VMM. Various mechanisms, such as the caching of emulation code or hardware assists , have been proposed to make the patching process more efficient. A different approach is that of paravirtualization , which requires guest operating systems to be modified ( ported ) before running in the virtual environment. This section presents some relevant architectures and how they relate to

1098-493: Is also used to implement the "guest" environments, and applications running in a given "guest" environment view it as a stand-alone system. The pioneer implementation was FreeBSD jails ; other examples include Docker , Solaris Containers , OpenVZ , Linux-VServer , LXC , AIX Workload Partitions , Parallels Virtuozzo Containers, and iCore Virtual Accounts. A snapshot is a state of a virtual machine, and generally its storage devices, at an exact point in time. A snapshot enables

1159-463: Is an example of such snapshots. Restoring a snapshot consists of discarding or disregarding all overlay layers that are added after that snapshot, and directing all new changes to a new overlay. The snapshots described above can be moved to another host machine with its own hypervisor; when the VM is temporarily stopped, snapshotted, moved, and then resumed on the new host, this is known as migration. If

1220-548: Is capable of running Windows XP applications inside a built-in virtual machine. Furthermore, moving already existing virtualized environments into a cloud, following the Infrastructure as a Service (IaaS) approach, is much more complicated if the destination IaaS platform does not support nested virtualization. The way nested virtualization can be implemented on a particular computer architecture depends on supported hardware-assisted virtualization capabilities. If

1281-484: Is sensitive because it allows access to the entire status register, which includes not only the condition codes but also the user/supervisor bit, interrupt level, and trace control. In most later family members, starting with the MC68010 , the MOVE from SR instruction was made privileged, and a new MOVE from CCR instruction was provided to allow access to the condition code register only. The IA-32 instruction set of

SECTION 20

#1732790685671

1342-489: Is what distinguishes a VMM from the more general class of hardware emulation software. Unfortunately, even on an architecture that meets Popek and Goldberg's requirements, the performance of a virtual machine can differ significantly from the actual hardware. Early experiments performed on the System/370 (which meets the formal requirements of Theorem 1) showed that performance of a virtual machine could be as low as 21% of

1403-460: The 68451 MMU . However, aspects of its design, such as its 1 clock memory access penalty, made this configuration unpopular. Some vendors used their own MMU designs, such as Sun Microsystems in their Sun-2 workstation and Convergent Technologies in the AT&;T UNIX PC/3B1 . Popek and Goldberg virtualization requirements The Popek and Goldberg virtualization requirements are

1464-723: The CP-40 and SIMMON , which used full virtualization , and were early examples of hypervisors . The first widely available virtual machine architecture was the CP-67 /CMS (see History of CP/CMS for details). An important distinction was between using multiple virtual machines on one host system for time-sharing, as in M44/44X and CP-40, and using one virtual machine on a host system for prototyping, as in SIMMON. Emulators , with hardware emulation of earlier systems for compatibility, date back to

1525-582: The Compatible Time-Sharing System (CTSS). Time-sharing allowed multiple users to use a computer concurrently : each program appeared to have full access to the machine, but only one program was executed at the time, with the system switching between programs in time slices, saving and restoring state each time. This evolved into virtual machines, notably via IBM's research systems: the M44/44X , which used partial virtualization , and

1586-554: The IBM System/360 in 1963, while the software emulation (then-called "simulation") predates it. Process virtual machines arose originally as abstract platforms for an intermediate language used as the intermediate representation of a program by a compiler ; early examples date to around 1964 with the META II compiler-writing system using it for both syntax description and target code generation. A notable 1966 example

1647-547: The Parrot virtual machine and the .NET Framework , which runs on a VM called the Common Language Runtime . All of them can serve as an abstraction layer for any computer language. A special case of process VMs are systems that abstract over the communication mechanisms of a (potentially heterogeneous) computer cluster . Such a VM does not consist of a single process, but one process per physical machine in

1708-594: The Pentium processor contains 18 sensitive, unprivileged instructions. They can be categorized in two groups: The introduction of the AMD-V and Intel VT-x instruction sets in 2005 allows x86 processors to meet the Popek and Goldberg virtualization requirements. The effort needed to support virtualization on the IA-64 architecture is described in a 2000 article by Magenheimer and Christian. A "hyperprivileged" mode for

1769-592: The Squeak Virtual Machine , and Strongtalk . A related language that produced a lot of virtual machine innovation was the Self programming language, which pioneered adaptive optimization and generational garbage collection . These techniques proved commercially successful in 1999 in the HotSpot Java virtual machine. Other innovations include a register-based virtual machine, to better match

1830-706: The UltraSPARC architecture was specified in UltraSPARC Architecture 2005 .' It defines a sun4v platform which is a super-set of the sun4u platform, but is still compliant to the SPARC v9 Level-1 specification. All sensitive instructions in the PowerPC instruction set are privileged. The efficiency requirement in Popek and Goldberg's definition of a VMM concerns only the execution of non-privileged instructions, which must execute natively. This

1891-402: The 'host', and the virtual machine emulated on that machine is generally referred to as the 'guest'. A host can emulate several guests, each of which can emulate different operating systems and hardware platforms. The desire to run multiple operating systems was the initial motive for virtual machines, so as to allow time-sharing among several single-tasking operating systems. In some respects,

Motorola 68010 - Misplaced Pages Continue

1952-474: The 68000 until the 68020 was introduced. Atari Games used the 68010 in some of their arcade boards such as the Atari System 1 . Some owners of Amiga and Atari ST computers and Sega Genesis game consoles replaced their system's 68000 CPU with a 68010 to gain a small speed boost. In practice, the overall speed gain over a 68000 at the same frequency is less than 10%. The 68010 could be used with

2013-635: The 68010's small speed boost over the 68000 and its support for virtual memory, it can be found in a number of smaller Unix systems, both with the 68451 MMU (for example in the Torch Triple X ), and with a custom MMU (such as the Sun-2 Workstation , AT&T UNIX PC/3B1 , Convergent Technologies MiniFrame, Plexus P/15 and P/20, NCR Tower XP, Apollo Computer 's DN300 and DN320 , and HP 9000 Model 310) and various research machines. Most other vendors (such as Apple Computer) stayed with

2074-643: The IBM CP-40 and CP-67 , predecessors of the VM family. Examples outside the mainframe field include Parallels Workstation , Parallels Desktop for Mac , VirtualBox , Virtual Iron , Oracle VM , Virtual PC , Virtual Server , Hyper-V , VMware Fusion , VMware Workstation , VMware Server (discontinued, formerly called GSX Server), VMware ESXi , QEMU , Adeos , Mac-on-Linux, Win4BSD, Win4Lin Pro , and Egenera vBlade technology. In hardware-assisted virtualization,

2135-445: The VM continues operation from the last-known coherent state, rather than the current state, based on whatever materials the backup server was last provided with. Nested virtualization refers to the ability of running a virtual machine within another, having this general concept extendable to an arbitrary depth. In other words, nested virtualization refers to running one or more hypervisors inside another hypervisor. The nature of

2196-457: The VM for a location on its physical disk are transparently translated into an operation on the corresponding file. Once such a translation layer is present, however, it is possible to intercept the operations and send them to different files, depending on various criteria. Every time a snapshot is taken, a new file is created, and used as an overlay for its predecessors. New data is written to the topmost overlay; reading existing data, however, needs

2257-401: The abstraction of a virtual machine. There are three properties of interest when analyzing the environment created by a VMM: In the terminology of Popek and Goldberg, a VMM must present all three properties. In the terminology used in the reference book of Smith and Nair (2005), VMMs are typically assumed to satisfy the equivalence and resource control properties, and those additionally meeting

2318-420: The base address for the exception vector table. The 68000 vector table was always based at address zero. A "loop mode" accelerates loops consisting of only a "loopable" instruction and a DBcc (Decrement/Branch on condition); an example would be MOVE and DBRA. The two-instruction mini-loop opcodes are prefetched and held in the 6-byte instruction cache while subsequent memory read/write cycles are only needed for

2379-449: The cluster. They are designed to ease the task of programming concurrent applications by letting the programmer focus on algorithms rather than the communication mechanisms provided by the interconnect and the OS. They do not hide the fact that communication takes place, and as such do not attempt to present the cluster as a single machine. Unlike other process VMs, these systems do not provide

2440-404: The data operands for the duration of the loop. It provided for performance improvements averaging 50%, as a result of the elimination of instruction opcodes fetching during the loop. The MC68012 variant, in addition to its memory space being extended to 2 GiB, also added a read-modify-write cycle (RMC) pin, indicating that an indivisible read-modify-write cycle in progress, in order to help

2501-412: The design of multiprocessor systems with virtual memory. The expansion of the memory space in the 68012 caused an issue for any programs that used the high byte of an address to store data, a programming trick that was successful with those processors that only have a 24-bit address bus (68000 and 68010). A similar problem affected the 68020 . The 68010 was never as popular as the 68000. However, due to

Motorola 68010 - Misplaced Pages Continue

2562-406: The development of hardware assists for the System/370 was virtual memory itself. When the guest was an operating system that itself implemented virtual memory, even non-privileged instructions could experience longer execution times - a penalty imposed by the requirement to access translation tables not used in native execution (see shadow page tables ). Virtual machines In computing ,

2623-411: The developmental stage, so it runs inside a sandbox . Virtual machines have other advantages for operating system development and may include improved debugging access and faster reboots. Multiple VMs running their own guest operating system are frequently engaged for server consolidation. A process VM, sometimes called an application virtual machine , or Managed Runtime Environment (MRE), runs as

2684-488: The following (sufficient) conditions. Theorem 2 . A conventional third-generation computer is recursively virtualizable if: Some architectures, like the non-hardware-assisted x86 , do not meet these conditions, so they cannot be virtualized in the classic way. But architectures can still be fully virtualized (in the x86 case meaning at the CPU and MMU level) by using different techniques like binary translation, which replaces

2745-931: The hardware provides architectural support that facilitates building a virtual machine monitor and allows guest OSes to be run in isolation. Hardware-assisted virtualization was first introduced on the IBM System/370 in 1972, for use with VM/370 , the first virtual machine operating system offered by IBM as an official product. In 2005 and 2006, Intel and AMD provided additional hardware to support virtualization. Sun Microsystems (now Oracle Corporation ) added similar features in their UltraSPARC T-Series processors in 2005. Examples of virtualization platforms adapted to such hardware include KVM , VMware Workstation , VMware Fusion , Hyper-V , Windows Virtual PC , Xen , Parallels Desktop for Mac , Oracle VM Server for SPARC , VirtualBox and Parallels Workstation . In 2006, first-generation 32- and 64-bit x86 hardware support

2806-472: The native machine in some benchmarks. The cost of trapping and emulating privileged instructions in the VMM can be significant. This led the IBM engineers to introduce a number of hardware assists , which roughly doubled the performance of the System/370 virtual machines. Assists were added in several stages. In the end, there were over 100 assists on the late models System/370. One of the main driving factors for

2867-416: The older snapshots are kept in sync regularly, this operation can be quite fast, and allow the VM to provide uninterrupted service while its prior physical host is, for example, taken down for physical maintenance. Similar to the migration mechanism described above, failover allows the VM to continue operations if the host fails. Generally it occurs if the migration has stopped working. However, in this case,

2928-486: The overlay hierarchy to be scanned, resulting in accessing the most recent version. Thus, the entire stack of snapshots is virtually a single coherent disk; in that sense, creating snapshots works similarly to the incremental backup technique. Other components of a virtual machine can also be included in a snapshot, such as the contents of its random-access memory (RAM), BIOS settings, or its configuration settings. " Save state " feature in video game console emulators

2989-473: The performance property are called efficient VMMs . Popek and Goldberg describe the characteristics that the instruction set architecture (ISA) of the physical machine must possess in order to run VMMs which possess the above properties. Their analysis derives such characteristics using a model of "third generation architectures" (e.g., IBM 360, Honeywell 6000, DEC PDP-10) that is nevertheless general enough to be extended to modern machines. This model includes

3050-421: The resources of a computer to be partitioned via the kernel . The terms are not universally interchangeable. A "virtual machine" was originally defined by Popek and Goldberg as "an efficient, isolated duplicate of a real computer machine." Current use includes virtual machines that have no direct correspondence to any real hardware. The physical, "real-world" hardware running the VM is generally referred to as

3111-440: The same computer (e.g., Windows , Linux , or prior versions of an operating system) to support future software. The use of virtual machines to support separate guest operating systems is popular in regard to embedded systems . A typical use would be to run a real-time operating system simultaneously with a preferred complex operating system, such as Linux or Windows. Another use would be for novel and unproven software still in

SECTION 50

#1732790685671

3172-453: The same physical page by a technique termed kernel same-page merging (KSM). This is especially useful for read-only pages, such as those holding code segments, which is the case for multiple virtual machines running the same or similar software, software libraries, web servers, middleware components, etc. The guest operating systems do not need to be compliant with the host hardware, thus making it possible to run different operating systems on

3233-506: The sensitive instructions that do not generate traps, which are sometimes called critical instructions. This additional processing however makes the VMM less efficient in theory, but hardware traps have non-negligible performance cost as well. A well-tuned caching binary translation system may achieve comparable performance, and it does in the case of x86 binary translation relative to first generation x86 hardware assist, which merely made sensitive instructions trappable. Effectively this gives

3294-415: The standard system. As technology evolves virtual memory for purposes of virtualization, new systems of memory overcommitment may be applied to manage memory sharing among multiple virtual machines on one computer operating system. It may be possible to share memory pages that have identical contents among multiple virtual machines that run on the same physical machine, what may result in mapping them to

3355-520: The underlying hardware, rather than a stack-based virtual machine, which is a closer match for the programming language; in 1995, this was pioneered by the Dis virtual machine for the Limbo language. In full virtualization, the virtual machine simulates enough hardware to allow an unmodified "guest" OS (one designed for the same instruction set ) to be run in isolation. This approach was pioneered in 1966 with

3416-429: The virtual machine's state at the time of the snapshot to be restored later, effectively undoing any changes that occurred afterwards. This capability is useful as a backup technique, for example, prior to performing a risky operation. Virtual machines frequently use virtual disks for their storage; in a very simple example, a 10- gigabyte hard disk drive is simulated with a 10-gigabyte flat file . Any requests by

3477-660: The virtual machine, notably in UCSD Pascal (1978); this influenced later interpreters, notably the Java virtual machine (JVM). Another early example was SNOBOL4 (1967), which was written in the SNOBOL Implementation Language (SIL), an assembly language for a virtual machine, which was then targeted to physical machines by transpiling to their native assembler via a macro assembler . Macros have since fallen out of favor, however, so this approach has been less influential. Process virtual machines were

3538-510: The virtualization requirements. The PDP-10 architecture has a few instructions which are sensitive (alter or query the processor's mode) but not privileged. These instructions save or restore the condition codes containing USER or IOT bits: All sensitive instructions in the System/370 are privileged: it satisfies the virtualization requirements. The Motorola MC68000 has a single unprivileged sensitive instruction: This instruction

3599-427: Was found to rarely offer performance advantages over software virtualization. In OS-level virtualization, a physical server is virtualized at the operating system level, enabling multiple isolated and secure virtualized servers to run on a single physical server. The "guest" operating system environments share the same running instance of the operating system as the host system. Thus, the same operating system kernel

3660-479: Was popularized around 1970 by Pascal , notably in the Pascal-P system (1973) and Pascal-S compiler (1975), in which it was termed p-code and the resulting machine as a p-code machine . This has been influential, and virtual machines in this sense have been often generally called p-code machines. In addition to being an intermediate language, Pascal p-code was also executed directly by an interpreter implementing

3721-548: Was the O-code machine , a virtual machine that executes O-code (object code) emitted by the front end of the BCPL compiler. This abstraction allowed the compiler to be easily ported to a new architecture by implementing a new back end that took the existing O-code and compiled it to machine code for the underlying physical machine. The Euler language used a similar design, with the intermediate language named P (portable). This

SECTION 60

#1732790685671
#670329