VPX

Key takeaways

VPX belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect VPX to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of VPX from memory before moving on to harder problems.

Reference excerpt

VPX, also known as VITA 46, is a set of standards for connecting components of a computer (known as a computer bus), commonly used by defense contractors. Some are ANSI standards such as ANSI/VITA 46.0–2019. VPX provides VMEbus-based systems with support for switched fabrics over a new high speed connector. Defined by the VMEbus International Trade Association (VITA) working group starting in 2003, it was first demonstrated in 2004, and became an ANSI standard in 2007.

History VPX was intended to address shortcomings in scalability and performance on both sides of the bus to bus bridging technology. The goal was to include newer faster VMEbus standards and new generations of PCI bus standards. The VMEbus International Trade Association (VITA) working group, formed in March 2003, was composed of companies such as ADLINK, Boeing, Curtiss-Wright, Elma Electronic, GE Intelligent Platforms, Kontron, Mercury Computer Systems, and Northrop Grumman, it was designed with defense applications in mind, with an enhanced module standard that enables applications and platforms with superior performance. VPX retained VME's Eurocard form factors, which are based on multiples of three rack units: 3U means three rack units, and 6U six rack units. It supported PCI Mezzanine Card (PMC) and XMC mezzanines (PMC with high-speed serial fabric interconnect), and maintaining the maximum possible compatibility with VMEbus. New generations of embedded systems reflected the growing significance of high speed serial switched fabric interconnects such as PCI Express, RapidIO, Infiniband and 10 Gigabit Ethernet. These technologies are replacing traditional parallel communications bus architectures for local communications, because they offer significantly greater capability. Switched fabrics technology supports the implementation of multiprocessing systems that require the fastest possible communications between multiple processors, such as digital signal processing applications. VPX gives the existing base of VMEbus users access to these switched fabrics. VPX technology was presented at a VMEbus International Trade Association (VITA) trade show in 2004, by a company called American Logic Machines USA. Products were announced as early as 2006.

Specification Technologies in VPX include:

Both 3U and 6U formats New 7-row high speed connector rated up to 6.25 Gbit/s Choice of high speed serial fabrics PMC, FMC (VITA 57), and XMC (VITA 42) mezzanines Hybrid backplanes to accommodate VME64, VME320 VXS, and VPX boards VPX - bus to bus bridges The VPX standard was updated in 2013 and 2019. In common with other similar standards, VPX comprises a "base line" specification, which defines the basic mechanical and electrical elements of VPX, together with a series of "dot level" specifications, one or more of which must be implemented to create a functional module. The specifications and their status are:

Connector The single biggest difference between original VMEbus boards and VPX boards is a new connector, developed by Tyco Electronics and known as the MultiGig RT2 which was used in VXS. Amphenol Aerospace has since developed their RVPX line of connectors capable of speeds up to 32 Gbit/s. VPX boards cannot be used in a standard VMEbus chassis, although the use of hybrid chassis is foreseen by the VPX standard. A 6U VPX board features six 16-column 7-row RT2/RVPX connectors and one 8-column 7-row RT2/RVPX connector, while a 3U board features two 16-column 7-row RT2/RVPX connectors and one 8-column 7-row RT2/RVPX connector. Also new for VPX boards are alignment/keying blocks which are designed to be sufficiently robust to prevent pin stubbing. The blocks also provide card keying and a safety ground. A 6U board has three such keying blocks, while a 3U board has two. The MultiGig RT2 connector is specifically designed to enable high performance. It accomplishes this through a 7-row 16-wafer (wafers can be power, differential signaling or single-ended) that delivers highly controlled impedance, minimal insertion loss and less than 3% crosstalk at transfer rates up to 6.25 Gbit/s. The new connector enables a 6U VPX board to feature a total of 707 non-power electrical contacts and a total of 464 signal contacts. The latter are usable as:

64 signals implemented as 32 high speed differential pairs for core fabric 104 VME64 signals 268 for user I/O including 128 high speed differential pairs (giving a total of 160 high speed differential pairs) 28 for system utilities or spares The connector is designed to allow a typical stiffening bar and a standard length PMC.

Power and ruggedization The VITA 62 section of the VPX standard allows for more flexibility in maximizing power capability of the system, as compared to the old VMEbus standards. "When the shared pins are utilized with multiple supplies, there are no real limitations on achievable power levels," states Patrick Shaw the chair of VITA 62. Removing wasted heat is always one of the primary objectives related to the power supply of a system. The specification of 6U VPX calls for computer cooling via a conduction-cooled envelope compliant with the IEEE standard IEEE-1101.2, which is compatible with existing enclosures. Provision is also made for air-cooling via an IEEE 1101.1/10 form factor version. For more stringent cooling requirements, the REDI (Ruggedized Enhanced Design Implementation – previously known as VITA 48) standard describes how to implement layout techniques to better support cooling methodologies on specific form factors. This provides a specification not only for ESD metal covers on two sides of VPX boards, but also for forced air, conduction- and liquid-cooling implementations. REDI also addresses spray cooling. To allow for greater power and heat dissipation, REDI includes provision for increased board-to-board spacing and increased board thickness.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with VPX

Start with the simplest possible case. Write down what VPX claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to VPX before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about VPX ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of VPX

In research: VPX appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses VPX in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: VPX is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer buses, so understanding it makes those chapters shorter.
In everyday life: Look for VPX outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study VPX in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what VPX means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain VPX out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is VPX in simple terms?

VPX, also known as VITA 46, is a set of standards for connecting components of a computer (known as a computer bus), commonly used by defense contractors. Some are ANSI standards such as ANSI/VITA 46.0–2019.

Why does VPX matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study VPX?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on VPX.