The battle lines were drawn in the 1990s between migration and emulation as the preservation strategy most likely to succeed. In the event neither has dominated, as we learn to place less trust in a single-strategy salvation and to develop ways of working and thinking that accommodate several approaches simultaneously.
Emulation is based on the principle of ‘simplify[ing] digital preservation by eliminating the need to keep old hardware working’ (Thibodeau, 2002, p.19).
Emulation and emulators are variously described and defined. In terms of preservation, emulation is ‘a means of overcoming technological obsolescence 1111
2 3 4 51 6 7 8 9 10 1 2 3111 4 5 6 7 8 9 20111 1 211 3 4 5 6 71 8 9 30111 1 2 3 4 5 6 7 8 9 40111 1 2 3 44 45 46 47 48 49 50111
‘Preserve technology’ approaches 129
of hardware and software by developing techniques for imitating obsolete systems on future generations of computers’ (Jones and Beagrie, 2001, p.105).
Emulation is the ability of a program or device to imitate another program or device, using software ‘that makes one technology behave as another’ (UNESCO, 2003, p.144). It ‘combines software and hardware to reproduce in all essential characteristics the performance of another computer of a different design, allowing programs or media designed for a particular environment to operate in a different, usually newer environment’. Emulators, ‘programs that translate code and instructions from one computing environment so it can be properly executed in another’, are required (Kenney et al., 2003).
Emulation is a well-established principle in the computing industry. Emul- tion can be of operating systems (for example, VirtualPC, which allows PC soft- ware to be run on an Apple Macintosh), of hardware platforms (for example, Kaypro or Apple II machines can be emulated on a PC), and of software appli- cations (for example, arcade games emulated through the MAME project).
One emulator in common use is built into the Apple Macintosh operating system and enables this computer to run software developed for earlier Apple computers. Printers are often designed to emulate Hewlett-Packard printers:
here, notes the Webopedia definition (www.webopedia.com), ‘emulation tricks the device into believing it [is] really some other device’. Terminal emulation is also common, so that a PC, for example, can be used as a terminal connected to a larger computer; these were once very common in mainframe computer environments. Although emulation is often associated with computer games, such as emulators that allow Sony PlayStation games to be played on a PC, it is an essential part of computing in all areas. The web is a fruitful source of information about emulators (e.g. www.directory.net/Computers/Emulators).
Both hardware emulation and software emulation have been experimented with to determine their feasibility for preserving digital materials. The aim is to make ‘future technologies behave like the original environment of a preserved digital object, so that the original object could be presented in its original form from the original data stream’ (UNESCO, 2003, p.144). Emulation of hardware has the attraction of being applicable to a wide range and large amounts of digital materials, because it ‘would allow a range of systems and digital objects to operate, thus solving the problem for a very wide range of digital objects’
(UNESCO, 2003, p.144). The same widespread applicability applies to emula- tion of operating systems. Emulation of software applications is less in favour, because it is more limited in its use and the effort and level of skill required to develop a complex piece of emulator software that can be used for only a small number of digital materials may be too high for this to be an option in most preservation situations.
Emulation has been investigated in several major projects, most notably, the CAMiLEON (Creative Archiving at Michigan and Leeds) project which inves- tigated emulation, testing available emulators and constructing an emulator for the BBC Domesday Project. Among its conclusions was that ‘emulation is not necessarily superior to migration for preserving the original look and feel of complex digital objects’. (The project’s web site (www.si.umich.edu/
CAMILEON) provides more information.) However, more research was needed, as this was a study of limited scope (Hedstrom and Lampe, 2001). Project NEDLIB (Networked European Deposit Library) ran from 1998 to 2000 and was based at the Koninklijke Bibliotheek in The Hague. One of its activities was to
130 ‘Preserve Technology’ Approaches: Tried and Tested Methods
conduct an experiment using commercial emulation tools to investigate the feasi- bility of emulation for digital preservation. This experiment, conducted by Rothenberg, was limited in its scope. It concluded that emulation should work in principle, but that further investigation is required to demonstrate that it can also work in practice (Rothenberg, 2000). The project’s web site (www.kb.nl/
coop/nedlib) gives more information.
Jeff Rothenberg’s name is firmly linked with emulation as a digital preserva- tion strategy. He has been a strong proponent of emulation as the only digital strategy that is likely to be effective. His argument is that the only way to make sure that digital materials are preserved in their native form (so that they are experienced appropriately by future users) and are not corrupted is to run soft- ware that interprets the bit-stream correctly. Because software can behave differently in different contexts, we should not expect software developed in the future to reproduce the behaviour of obsolete software. To ensure the appro- priate behaviour of digital materials it is necessary to run the original software used to view the document in its native form.
Rothenberg points out that all digital materials depend on software, and in particular many new kinds of digital materials are ‘inherently digital’ and ‘can- not be meaningfully represented as page images’ (Rothenberg, 2003). This means that preservation strategies such as saving page images are of little use for the preservation of much digital material. Emulation, according to Rothenberg, is the only preservation approach that has multiple advantages and capabilities, among them preserving executable digital objects (objects in which software pro- grams are embedded), providing a ‘single, consistent way’ of preserving all kinds of digital materials, reducing the effort expended in preserving individ- ual artifacts (except for copying the bit-stream onto new media), and minimizing the need to understand record formats. Despite his strong advocacy of emula- tion, Rothenberg suggests that a mixed strategy approach is most feasible, with emulation used ‘if original behavior is needed; oras a cheap backup, to preserve everything’ (Rothenberg, 2003).
Other authorities also suggest that emulation has potential. Jones and Beagrie consider it to be one of only two primary strategies (those suitable for medium to long-term preservation of digital materials), the other being migration (Jones and Beagrie, 2001, p.103). They suggest that it has the advantage over other methods of recreating the look and feel and functionality of the original digital material, as well as the potential for avoiding the high costs associated with repeated migration. Emulation, by their judgement, has good prospects for preserving complex digital materials (Jones and Beagrie, 2001, p.105). The UNESCOGuidelinesnote that emulation is already well established and under- stood in computing, that many emulators already exist for a variety of hardware and software platforms, and that it has the potential to ‘allow a range of digital objects to be recreated with full functionality, including software objects, using the original, untransformed data stream in combination with original preserved software’ (UNESCO, 2003, p.145).
Not all share Rothenberg’s enthusiasm, among them Granger (2000). The arguments against emulation form a list as long as the arguments in its favour (Jones and Beagrie, 2001, p.105; UNESCO, 2003, p.145). Chief among them is that emulation has not been sufficiently tested in practice. Also high on the list of disadvantages is the high cost of developing emulators, which may be greater than the costs of repeated migration, because it requires high levels of 1111
2 3 4 51 6 7 8 9 10 1 2 3111 4 5 6 7 8 9 20111 1 211 3 4 5 6 71 8 9 30111 1 2 3 4 5 6 7 8 9 40111 1 2 3 44 45 46 47 48 49 50111
‘Preserve technology’ approaches 131
expertise to write complex software. There is some scepticism about the ability of emulation to do all that is claimed, and it may not be possible to emulate fully all of the functionality of the original, nor all of its look and feel. The lack of adequate documentation of hardware and software may frustrate emulation attempts. Copyright issues associated with ownership of software code may impede emulator development. Users may have problems in interacting with
‘archaic applications operating under emulation’, and the need either to migrate the emulators themselves or emulate the emulators raises the interesting spectre of ‘layers upon layers of emulators’ (UNESCO, 2003, p.145).
If emulation is to be attempted, then the requirements are many and varied.
Appropriate expertise is, of course, essential. Documentation of the systems to be emulated needs to be comprehensive and accurate. The emulation software should be written in open source code, using a ‘standard programming language with good prospects for longevity and future compatibility’ (UNESCO, 2003, p.145) and following best industry practice, including thorough documentation.
Probably the most widely reported emulation project carried out for preser- vation purposes to date is the BBC Domesday Project. Abbott (2003), Darlington, Finney and Pearce (2003), Mellor (2003), National Archives (U.K.) (2004?) are just some of the reports on this project; the CAMiLEON web site (www.si.umich.
edu/CAMILEON/domesday/domesday.html) is also a useful source. The original Domesday Project, undertaken from 1984 to 1986, surveyed the UK to celebrate the 900th birthday of the Domesday Book. It cost about ?2.5 million and involved about one million school children from 14 000 British schools. The resulting images and text were recorded on two 12-inch videodisks that were accessed using a LV-ROM (LaserVision Read Only memory) player attached to a BBC Master computer with additional software and hardware (Abbott, 2003, p.7). As part of its activities the CAMiLEON Project developed an emulation of the original Domesday system hardware.
The process of developing this emulation involved migrating the data files from the videodisks to current media, and developing software that emulates the BBC Master computer and the laserdisk player (Mellor, 2003). Image files were re-digitized from the original one-inch analogue videotapes (Darlington, Finney and Pearce, 2003). The need to avoid the obsolescence of the emulation software was kept in mind: ideally, the software should not be limited to oper- ation on any specific operating system or type of computer so that it will be easier to run on future computers. In the end, however, the BBC Domesday emulator that was developed runs only on the Windows operating system (Mellor, 2003, p.8).
Significant lessons were learned from the BBC Domesday Project. This emula- tion project was hampered by lack of documentation and software to test the emulation, but was fortunate to have available a working original system, albeit a fragile one. This was important because it allowed the developers to ‘compare with and validate the migrated system’, which has special significance in a multi- media system ‘where the look-and-feel and user interaction is important’
(Darlington, Finney and Pearce, 2003). Wheatley, one of the team who worked on this project, summarizes the issues:
Most of the really difficult problems we faced were due to the long time gap between the creation of Domesday and its preservation. If we had conducted the rescue 10 years earlier it would have been far easier. The
132 ‘Preserve Technology’ Approaches: Tried and Tested Methods
timeliness of preservation work is a crucial issue that Domesday really underlines. Would we be able to rescue Domesday if we left it another 10 years? I’m sure we could, but it would be at far greater expense (Abbott, 2003, p.10).
Emulation is likely to play a significant role as a major preservation strategy. It has been sufficiently well tested to show promise. What is now required to exploit that promise is the allocation of significant resources, probably through collaborative action, to develop a range of emulators. Emulation is unlikely to be the ‘magic bullet’ (Lynch, 2004), the single solution to digital preservation, as it is sometimes promoted. Nor is it likely to replace migration as a primary digital preservation strategy, because emulators will themselves need to be migrated. Holdsworth and Wheatley remind us that emulation should not be over-sold as the answer to all digital preservation issues. It is just part of the armoury necessary for defending our digital heritage against the ravages of time in a world where innovation (and hence change) is highly prized (Holdsworth and Wheatley, 2001).
We can envisage that emulation will be used increasingly as more emulators are developed, in specific situations, such as for complex digital materials or for those which contain executable software that will only run on specific hardware, or for digital materials that need to be viewed in their original environ- ment. These, of course, presuppose that suitable emulators are already available or that the expertise is available to develop them (UNESCO, 2003, p.145).