Backward compatibility

An excellent way to export information from SAS to another SAS user is with PROC CPORT. PROC CPORT creates an operating system-independent SAS transport file that can hold data sets as well as SAS programs, permanent format catalogs, and other SAS catalogs. Note that PROC CPORT files are not backward compatible with older versions of SAS, so a transport file created by PROC CPORT in SAS 9 cannot be read by SAS 8. Here is some example code showing how to place all of the SAS data sets and permanent formats from a libref called library into a SAS transport file called mytrial.xpt. ... 

Modifications to code, including bug fixes, that can override or patch existing code in another package (with certain restrictions ensuring backward compatibility). 

A new version is backward-compatible from a user s point of view. The new material is only an extension of the old. If the contents are program code, then the code may be different, but it should at least meet the previous version s spec. 

A complementary approach is to conduct the assays under high-throughput automated conditions. This can be either through the miniaturization of assays, that is, 96-384 plates and if possible 1536, or through the use of alternative assay technologies (e.g., microfluidics). Both scenarios require studies of equivalency testing and backwards compatibility with previous methods and results. 

In 1983, SPICE 2G.6 was released and remained the industry standard for many years. Motivated by the increased use of UNIX workstations and superior programming tools, SPICE 2 was converted into the C programming language and released as SPICE 3. Although SPICE 3 is not entirely backward compatible with SPICE 2, the new features far outweigh this drawback. SPICE 3 has a technical advantage of being readily modified because it is written in C. SPICE 3 also offers more and improved device models and analysis functions. 

Backwards compatible multichannel coding adds the option of forward and backwards compatible coding of multichannel signals including the 5.1 channel configuration known from cinema sound. 

ISO/IEC IS 13818-7 is called MPEG-2 Advanced Audio Coding and covers a new, non backwards compatible audio coding system for flexible channel configurations including stereo and multichannel services. 

Suppliers usually make sure their products are backward compatible so that legacy systems can be seamlessly replaced by new systems. Suppliers typically develop their upgrades for use on the same hardware platform. Full compatibility, however, is more than this. The new product must... 

If you have a computer made before 1997, chances are the motherboard in your computer has a few Industry Standard Architecture (ISA) slots. They re easily recognizable as they are usually brown and have two parts, a shorter part and a longer part. Computers made after 1997 generally include a few ISA slots for backward compatibility with old expansion cards. 

Be careful not to assume that data flows at the same speed within the processor as it does outside of the processor. Some Intel processors have an internal data bus that is greater than the external data bus. The 8088 and 80386SX are good examples of this. They are designed with an internal bus that has twice the width of the external bus. This provides for backward compatibility with other processors that do not support a wider bus. 

After a time, the first major improvement to SCSI-1 was introduced. Known as SCSI-2 (ANSI Standard document X3.131-1994), it improved SCSI-1 by allowing for more options. These options produced several subsets of SCSI-2, each having its own name and characteristics. But the most obvious change from SCSI-1 is that SCSI-2 now uses a higher-density connector (see Figure 4.14). Also, SCSI-2 is backward compatible with SCSI-1 devices. 

One interesting thing about the ISA bus is that it is backward compatible with the older, 8-bit bus. ISA bus slots are basically 8-bit slots with the extra signal lines required to make them 16-bit on a second connector. Expansion cards made for the PC s 8-bit bus can be inserted into ISA slots and they will function properly. There is one exception, however. Some 8-bit cards have a skirt extending below the bus slot. This skirt will not allow the 8-bit card to be inserted all the way into the ISA slot. It is for this reason that you will sometimes have 8-bit slots mixed in with ISA slots on the same motherboards. 

One special case exists for interrupts when configuring them. You will notice that some interrupts are cascaded to each other. What this means is that in an ISA system, when the computer needs to access an interrupt higher than 9, it uses IRQ 2 to get to it. This method ensures backward compatibility with 8-bit buses. 

There were several new, desirable features introduced with EISA. Its creators took the best of MCA s features and added to them. As we have already mentioned, EISA has a 32-bit data path. Additionally, it has more FO addresses, it allows expansion cards to be set up using software, there is no need for interrupts or DMA channels, and it allows for multiple bus-mastering devices. However, despite all these advances, it still uses the 8MHz clock speed of ISA (to ensure backward compatibility with ISA cards). 

The Video Electronics Standards Association (VESA) was formed for this reason. This group made sure that cards made for one vendor s slot would work in another vendor s computer. As time passed, the slot design changed and was given a new name, the VESA Local Bus slot (and was also known variously as VL-Bus, VLB, or just VESA, after the group that came up with the standard). This slot was a 32-bit addition to the ISA bus and was therefore backward compatible with it. 

The final two features of PCI that we should discuss are its backward compatibility and software setup features. The PCI bus uses a chipset that works with PCI, ISA, and EISA. It is possible to have a PC that contains all these buses on the same motherboard. Also, the PCI cards are mostly Plug and Play. The cards will automatically configure themselves for IRQ, DMA, and I/O port addresses. 

The first release of the PCMCIA standard (PCMCIA 1, the same used in that original handheld computer) defined only the bus to be used for memory expansion. The second release (PCMCIA 2) is the most common it is in use throughout the computer industry and has remained relatively unchanged. PCMCIA 2 was designed to be backward compatible with version 1, so memory cards can be used in the version 2 specification. 

Because they are very similar architecturally, applications written for Windows 95 will work with Windows 98, and those written for Windows NT will work with Windows 2000. Those written for the newer systems, however, are not always backward compatible. 

Transparency. Schema evolution should result into minimal or no degradation of availability or performance of the changed system. Furthermore, applications and other schema consumers should largely be isolated from the changes, e.g., by support for backward compatibility, versioning, or views. 

Generates views to -support both forward and backward compatibility, when formally possible... 

Commercial software (currently, Microsoft, Corel, AutoDesk, etc.) upgrades that are issued every year or two should be evaluated for backward compatibility, bugs, and security flaws. Lack of compatibility may prevent opening some files and corrupt others. Replacement of specific scientific software should be evaluated for consistency in aspects such as look-up tables, algorithms and calculation routines. 

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