Jumping on the PCI Bus: Part 1 of a 2-Part Series

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For months, AS/400 and iSeries owners have experienced plenty of confusion over the impending migration of their server's I/O architecture from IBM's proprietary System Product Division (SPD) bus to one based on the industry-standard Peripheral Component Interface (PCI). Fortunately, recent IBM announcements and statements from sources within the company have cleared up many misconceptions about the migration.

 

In this issue and the one to follow, I'll walk you through those statements and provide the information you'll need to decide about migrating your SPD devices to PCI. Since this is a complex topic, I'll start by reviewing how and why IBM is switching to PCI. Before we dive in, I need to warn you that unless you're a hardware maven, some of this may make your head hurt. Stay with me, however, because your budget may hurt a lot more than your head if you don't act on this information soon.

PCI on the AS/400: A Brief History

In the mid-1990s, IBM decided that it could better meet the demands of AS/400 customers for more I/O bandwidth and functionality if it were to migrate the server from SPD to the PCI bus architecture. Since switching to PCI would eventually force customers to buy new expansion towers, I/O adapters, and I/O processors, the computer giant decided to phase in the change over a period of several years.

 

The migration began in 1997 when IBM shipped the entry-level Model 150 with a PCI bus. Over the next two years, the company expanded PCI support to the Models 170, 250, and 600, all of which used PCI exclusively. By contrast, the Models 620/S20--and later, the 720--came standard with PCI but supported SPD on an optional basis. Larger AS/400s--the Models 640/S30, 650/S40, and later the 730 and 740--remained SPD-only systems. In 1999, however, IBM made it possible for these systems to connect to PCI cards housed in the 5065 and 5066 Expansion Towers. While these towers utilize a PCI bus, they connect to the AS/400 via an SPD cable.

 

In late 2000, IBM took a big leap forward in its adoption of PCI. It announced that its newest family of servers--the iSeries 270 and 8xx series--would only offer native support for PCI. There are two important things to know about PCI support on these models:

  • First, the 270 and 8xx servers support a more modern version of PCI, known as PCI-node, that offers unique benefits, such as the ability to power down, remove, and power up PCI cards while the iSeries is still running. IBM announced several new PCI-node cards with the iSeries to support these servers.
  • Second, these servers no longer connect to I/O expansion towers via an SPD cable. Instead, they use copper or optical cables that comply with the High Speed Link (HSL) standard and are about ten times faster than the old SPD interconnects.

Today's 270 and 8xx models do not support SPD cards. They also don't support all of the original AS/400 PCI cards, since some PCI cards are not PCI-node compatible. However, 8xx owners can still support SPD cards and all of the original PCI cards running in expansion towers if the towers connect to the 8xx server via a migration tower, such as the 5034 or 5035. The following chart explains which AS/400 and iSeries models support SPD, PCI, and PCI-node cards.

 

AS/400 and iSeries Support for SPD, PCI, and PCI-Node Architectures

Models

SPD

PCI (Original)

PCI-node

AS/400 Models



150, 170, 250
No
Yes
No
4xx/5xx
Yes
No
No
600
No
Yes
No
620/S20/720
Optional
Yes
No
640/S30/730
Yes
Via 5065/66 Expansion Tower
No
650/S40/740
Yes
Via 5065/66 Expansion Tower
No
iSeries Models



270
No
No
Yes
8xx
Via Migration Tower
Via Migration Tower
Yes


How POWER4 and OS/400 V5R2 Change the PCI Picture

For months, AS/400 and iSeries owners have been wondering how IBM's PCI support will change when IBM announces OS/400 V5R2 and the new POWER4 family of iSeries servers in the second half of this year. On February 12, 2002, IBM announced several statements of direction that addressed customer concerns. (Click here to access the announcement.) These statements made it clear that:

  • OS/400 V5R2 will not run on the 4xx/5xx models, nor on any AS/400s announced before the 4xx/5xx series.
  • OS/400 V5R2 will, however, run on all 6xx, Sxx, 7xx, and 8xx models as well as the 270, and it will support SPD buses and devices on these models at their current support levels (as shown in the table above).
  • The POWER4 servers to be announced later this year will not attach to SPD devices, expansion towers (either SPD or PCI-based) that connect via an SPD cable, or migration towers. They will only directly attach to PCI-node expansion towers via HSL.

As you can see from the above statements, the I/O changes you'll have to make if you upgrade to a POWER4 iSeries are quite different from those if you upgrade to OS/400 V5R2 on your existing systems. Unfortunately, many customers have thought of these two upgrades as if they were a single transition. This has led to rumors that OS/400 V5R2 will not support SPD when in fact it will. It simply will not support SPD on the POWER4 family of systems.

 

Since installing OS/400 V5R2 and upgrading to POWER4 have different ramifications for your SPD assets, it's important that you develop your plans for these technologies on separate tracks and consider whether you will need one or both of them. I'll have more to say about those considerations when I return to this subject next week.

 

Lee Kroon is a Senior Industry Analyst for Andrews Consulting Group, a firm that helps mid-sized companies manage business transformation through technology. You can reach him at This email address is being protected from spambots. You need JavaScript enabled to view it..

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