The Worlds Best Computer

Introduction to the System i

The System i is the most advanced computer available to the general public. That is a bold statement, but who can point to another system that can run: i5/OS, AIX, POWER Linux, Windows, Intel Linux, Solaris and Netware operating systems and their applications, concurrently? I know of no other computer that can do this.

This machine is a true 64-bit computer. The operating system, objects and hardware are all 64-bit. The System i has been 64-bit since December 1995 and is in its 12^th generation of 64-bit processors.

Today the System i uses the IBM POWER6 processor running at 4.7 GHz. It should be noted that the POWER6 is architected to run at as high as 5.6 GHz and a single processor can support up to 1,000 LPARs (logical partitions). Intel cannot match this performance. In fact, the fastest Intel processor cannot go beyond 3.8 GHz in clock speed. At 4 GHz the Intel chip runs so hot that the gates may not close in the transistors. This in part accounts for the Intel strategy of using multiple cores all at slower clock speeds.

Even though the AS/400 and its successors, including the System i are used in 85% of the Fortune 500 businesses, this machine remains the least known of IBM’s hardware brands.

But what if you speak with IBM's customers? Then you will be very pleasantly surprised. Our customers are the most loyal and most satisfied of all IBM’s customers. Why? Because the System i is perhaps the most reliable machine in existence, it just runs and runs and runs. It is also the easiest to operate.

If you ask any System i trained person what makes the machine special, you’ll likely get an answer like “Single Level Store”. That’s a great answer but very few folks can explain single level store adequately.

Single level store relates to how the System I views where objects are located. Essentially everything stored on the System i: files, programs, and profiles, etc. are objects. All objects on the System I are referenced by name not by name at location as you do in Windows, UNIX and Linux. One way to look at this is that the ‘system’ acts as if all objects are currently in memory. The system views memory and disk as one big storage space.

Another perspective says that objects are not referenced by location since their location is likely to change if the system acts to optimize itself. In essence the most critical area of the System i architecture is its storage management.

System i Storage Management

The System I supports both internal (also known as integrated) storage as well as external (i.e. SAN) storage. The most prevalent in use is internal storage, and the way this is managed is elegant.

An object put onto the System i is scatter loaded across the available drives. This happens regardless of the protection scheme in effect (none, RAID5, RAID51, RAID6, or RAID10). This spreading of the data is not in and of itself anything special. It’s what happens next that makes it special.

The operating system, i5/OS will then manage each drive such that the occupancy across the drives is equal. Therefore, if there are 10 disk drives on the system, all 10 will show approximately the same level of space consumed.

Aside from occupancy, the system will also balance the arm busyness (also called spindle or actuator activity). As a general guideline, no given arm on the System i should ever be above 40% busy.

Disks may be added to the System i hot (while the system is running). The new drives will be flagged and then given higher priority for saving objects. When the system has spare CPU cycles it will perform its balancing act over time. Or the customer can issue a command and force balancing immediately across all drives (including the new one).

Since any given object is scatter loaded, when an object is called for execution and it is not already in memory, the system will queue up the arms to access the object in tandem, or in a coordinated fashion. The result is that I/O-bound applications are particularly faster on this machine than others. Database applications doing large table scans as well as random-I/O applications like those found in typical online transaction processing will be executed faster.

These two factors alone cause us to think of disk acquisitions differently on this machine. For example, the more arms the better. It will be better for instance to have 4 – 72 Gb. disk drives installed than 1 – 288 Gbs drive; the lesson is that four arms working is better than one. The smaller drives have less real estate for the arms to traverse to access the called upon object.

The most exciting aspect of System i storage management is that all the operating systems can exploit it to their benefit. For instance, a Windows server on the System i will never have to be defragged and windows disk drives can be dynamically expanded while Windows applications are active. You cannot do that with a Windows server from Dell, HP, Gateway or IBM, but you can do this with the System i.

A customer once asked me what I could do with Windows on a System i that I could not do on a free standing system. I told him that I could sit in Philadelphia and add disk to a system sitting in Chicago. Could he do that? The answer was of course not. And as an added bonus, the disk protection in effect for i5/OS would automatically, and transparently be extended to Windows, AIX, Linux, Solaris and/or Netware.