<story><title>Pub400.com – Your public IBM I 7.5 server</title><url>https://pub400.com/</url></story><parent_chain><item><author>bitwize</author><text>Is IBM i the thing formerly known as AS&amp;#x2F;400? IBM&amp;#x27;s new shiny next-millennium single letter branding is more confusing than their old-school letters-virgule-numbers branding.</text></item></parent_chain><comment><author>hlandau</author><text>One of the most interesting things about IBM i&amp;#x2F;AS&amp;#x2F;400 is its use of hardware memory tagging. There is a secret set of extensions to the PowerPC ISA which allows you to associate a tag bit with every 16 bytes of memory. This is used to implement a capability-based model where valid pointers can&amp;#x27;t be forged.&lt;p&gt;I write some more about it here:&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;www.devever.net&amp;#x2F;~hl&amp;#x2F;ppcas&quot; rel=&quot;nofollow&quot;&gt;https:&amp;#x2F;&amp;#x2F;www.devever.net&amp;#x2F;~hl&amp;#x2F;ppcas&lt;/a&gt;&lt;p&gt;Interestingly this functionality is actually unlocked on the Raptor Talos II&amp;#x2F;Blackbird systems so you can play with it in full.</text></comment>
<story><title>Pub400.com – Your public IBM I 7.5 server</title><url>https://pub400.com/</url></story><parent_chain><item><author>bitwize</author><text>Is IBM i the thing formerly known as AS&amp;#x2F;400? IBM&amp;#x27;s new shiny next-millennium single letter branding is more confusing than their old-school letters-virgule-numbers branding.</text></item></parent_chain><comment><author>skissane</author><text>Yes, but it also reflects the fact that it is no longer a separate hardware line.&lt;p&gt;In the beginning (1978) was the IBM System&amp;#x2F;38, which had a custom CISC CPU architecture with 48-bit addressing (called IMPI), vaguely resembling the 360&amp;#x2F;370 mainframe instruction set, but incompatible with it, and having some rather high-level abilities like task switching in microcode (similar to hardware task switching on the 386). The System&amp;#x2F;38 had some very advanced features: single level storage, capabilities and programs compiled to byte code (which the OS then converted to the IMPI physical instruction set). However, IBM also had its System&amp;#x2F;36 &amp;quot;midrange&amp;quot; line (basically minicomputers but IBM preferred to call their business-oriented minicomputers &amp;quot;midrange&amp;quot;), which was incompatible and more of a traditional system architecture. So in 1988 IBM &amp;quot;unified&amp;quot; them by releasing the AS&amp;#x2F;400, which was basically a version 2.0 of the System&amp;#x2F;38, keeping the same basic architecture but adding a System&amp;#x2F;36 emulation subsystem so it could run most System&amp;#x2F;36 applications.&lt;p&gt;Separately, IBM had its RISC Unix RS&amp;#x2F;6000 line, which spawned POWER and PowerPC. And then in 1991, IBM came out with a new version of the AS&amp;#x2F;400 based on PowerPC instead of proprietary IMPI CISC. The fact that applications compiled to bytecode meant most applications could be ported to RISC seamlessly, since the new OS version translated the bytecode to PowerPC instructions instead of IMPI instructions. At the same time, much of the core of the OS was rewritten in C++ (having previously been in a proprietary PL&amp;#x2F;I dialect.)&lt;p&gt;But still, although RS&amp;#x2F;6000 and AS&amp;#x2F;400 now used the same CPU architecture, they were still physically different hardware. Originally, the AS&amp;#x2F;400 used its own PowerPC chips with additional instructions the RS&amp;#x2F;6000 ones lacked. Even after they unified the two lines on the same CPU models, they still had different firmware.&lt;p&gt;In 2000, there was a marketing-driven decision (&amp;quot;eServer&amp;quot;) to rebrand RS&amp;#x2F;6000 to pSeries and AS&amp;#x2F;400 to iSeries. This was part of an attempt to present IBM&amp;#x27;s four distinct server platforms (mainframe, AS&amp;#x2F;400, RS&amp;#x2F;6000 and PC) as some kind of cohesive strategy (mainframe became zSeries and PC servers became xSeries).&lt;p&gt;Then, in 2006, the iSeries (formerly AS&amp;#x2F;400) and pSeries (formerly RS&amp;#x2F;6000) hardware lines were merged completely, to become IBM Power Systems. Now there was no physical difference between the hardware, it is just which OS you install on it. The IBM i (originally OS&amp;#x2F;400 and later i5&amp;#x2F;OS) operating system uses certain firmware features which AIX doesn&amp;#x27;t use – but all IBM Power Systems have that code in their firmware, it is just AIX and Linux don&amp;#x27;t call those functions. (There are now low-end Linux only machines which refuse to run AIX or IBM i, although possibly that&amp;#x27;s just a flag in the firmware license as opposed to distinct code.)</text></comment>