Happy Birthday, System/360

April 7, 2011

As an article at Wired reminds us, it was 47 years ago today, on April 7, 1964, that IBM first announced its System/360 family of what came to be called mainframe computers.  It was an announcement that heralded something that was, at that time, really new: a range of computers, with capacities ranging from modest to powerful,  that shared a common architecture, a (mostly) common machine instruction set, and the ability to share a set of common peripheral devices (such as tape and disk drives).  It was a huge gamble on IBM’s part: the company invested about $5 billion in developing a range of compatible hardware.

System/360 components included the CPU, control unit, display terminal, printer, data-cell storage, drum storage, disk storage and DASD control unit, tape storage, a tape control unit, card reader–card punch combination, console station and console typewriter.

Previously, computer systems had been, if not custom made for a particular installation, at least somewhat idiosyncratic affairs.  Manufacturer ABC’s Model Y might be a big improvement and have more capacity, compared to Model X, but it was unlikely to be easy to “upgrade”.

The really important idea behind the System/360, though, was much more important than compatible hardware: all the computers in the System/360 series had the same architecture, and could run the same programs.  The nascent idea of portable programming had already manifested itself in the development of high-level languages, like FORTRAN and COBOL.  But the System/360 promised more: portability at the machine code level; an Add Register (AR) instruction, or a Move Characters (MVC) instruction, meant the same thing across the range of System/360 models.  This was a degree of compatibility not seen previously; it meant that, if you had a program — an object code program — that ran on a System/360 Model 30, it would run, without changing or even re-compiling, on a System/360 Model 50.

IBM’s gamble was a huge commercial success.  The first System/360 machines were delivered in 1965; by a year later, IBM was selling ~1000 systems per month, at an average price of $2-3 million.

That success helped the System/360 establish some de facto standards, like the 8-bit byte and 4-byte words, which we still have.   (Previous computers had featured an odd array of word lengths, form 8 to 36 bits.)  The architecture also provided the first quasi-standard format for floating point data and computations, a standard that lasted until it was superseded by IEEE-754 floating point in 1985.  The project also produced some very fine documentation; that it could be useful across the product line probably helped convince everyone that it was worth doing the job well.  I still have my well-used copy of IBM System/360 Principles of Operation [GA22-6821], the architecture reference manual, which in my opinion is one of the finest examples of technical writing I have ever seen.  Fred Brooks, the project manager for the OS/360 operating system, wrote The Mythical Man-Month, which should be a must-read for any software project manager.

None of this is to say that the System/360 was perfect.  It had its share, at least, of ugly features, especially on the software side (The Mythical Man-Month has a few choice examples).   But there was enough fundamental sense in its design that it has lasted this long — as with UNIX, first released in 1969.   And, as I learned in a casual conversation recently, there is a small library of FORTRAN “helper” routines, for things like manipulation of special character strings and dates, that I wrote ~35 years ago,  in assembler for the System/360,  that is still going strong.

Microsoft Patch Tuesday Preview, April 2011

April 7, 2011

In keeping with its usual schedule, Microsoft released its Security Bulletin Advanced Notification for April, previewing the security fixes it plans to release next Tuesday, April 12.  The company plans to release a total of 17 security bulletins; thirteen of these are for Windows, three are for Microsoft Office, and one for the Visual Studio development tools.  There are nine bulletins rated Critical, and eight rated Important.  All supported releases of Windows are affected, each with several Critical vulnerabilities; the following table gives the breakdown by Windows version.

Windows Version Critical Important Moderate
Windows XP+SP3 7 6
Windows Vista 9 3
Windows Server 2003 5 5 2
Windows Server 2008 7 2 2
Windows 7 8 3
Windows Server 2008 R2 6 2 2

Microsoft’s announcement says that seven of these bulletins will definitely require a system restart; the rest may require a restart, depending on the configuration of your system.

As always, this information is subject to change between now and the actual release of the bulletins next Tuesday.  I will post a note here once the actual updates are available.

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