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The IBM 1130 Computing System was introduced in 1965. It was IBM's least-expensive computer to date, and was aimed at price-sensitive, computing-intensive technical markets like education and engineering. The IBM 1800 was a process control variant of the 1130 with one extra instruction and extra I/O capabilities.
The 1130 became quite popular, and the 1130 and its non-IBM clones gave many people their first feel of "personal computing." Though its price-performance ratio was good and it notably included inexpensive disk storage, it otherwise broke no new ground technically. The 1130 holds a place in computing history primarily because of the fondness its former users hold for it.
The IBM 1130 used System/360 electronics technology (SLT - Solid Logic Technology) and had a 16-bit binary architecture, not very different from later minicomputers like the PDP-11 or Data General Nova. The address space was 15 bits, limiting the 1130 to 32K 16-bit words of core memory. Indirect addressing used up the other bit. If the high order address bit was set, the address was treated as a pointer to another address. Amazing loops were possible.
Much programming was done in Fortran. The 1130 Fortran compiler could run on a machine with only 4 K words of core. That's 8 K bytes, the minimum file size on many PC's. Eastern Michigan University developed a Fortran IV compiler for the 1130.
The basic 1130 came with an IBM 2310 disk drive. These read pizza-box-sized 2315 single platter cartridges that held 512 K words or 1 M byte (less than a 3.5" floppy). Disk memory was used to store the operating system, object code, and data, but not source code. The last was kept on punch cards. The disk operating system was called DMS or DM2 (for Disk Monitor System, Release 2).
Other available peripherals included the IBM 1132 and IBM 1403 lineprinters, the IBM 1442 card reader/punch, the IBM 1311 Disk Drive and the IBM 1627 drum plotter. The plotter was very useful for engineering work. The console typewriter used an IBM Selectric mechanism, which meant one could change the type by replacing a hollow, golf-ball sized type element. There was a special type element available for APL, a powerful array-oriented programming language using a special symbolic notation.
A standard 1130 had a 3.6 microsecond memory cycle time, with a more expensive model equipped with 2.2 µs memory cycle time. (You could use the latter with a 1403 printer connected through a 1133 multiplexer.) To further tap the low end of the market, IBM introduced the 1130 Model 4, with a 5.6 µs cycle time - at a lower price of course. The Model 4's 1132 printer was derated as well, but the slower CPU still could not keep up with it. (The 1132 used the CPU to determine when to fire the print wheels as they rotated, a very compute intensive function.) Careful readers of the 1130 hardware manual discovered that when the printer interrupt level (4) was on, the 1130 Model 4 ran at the faster 3.6 us cycle time. Some users of the Model 4 would write a phony printer driver that turned on level 4 and left it on. They would call this driver when running a compute intensive job and write their output to disk, the printer being unusable, of course. When done, they'd run a normal program to print their output.
Sample Fortran Program Deck
The following listing shows a simple card deck that compiles and runs a Fortran program for the IBM 1130 when running DM2.
// JOB
// FOR
*LIST SOURCE PROGRAM
*IOCS(1132 PRINTER)
*ONE WORD INTEGERS
C-------------------------------------------------------
C PLOTS A SINE WAVE ON THE LINE PRINTER
C-------------------------------------------------------
DIMENSION LINE(80)
DATA ISPAC, ISTAR, IBAR /' ', '*', 'I'/
C
PI = 4.*ATAN(1.)
C
WRITE(3,10)
10 FORMAT('0 A SIN(A)', /, ' ----- ------ ------- ',
+8('----------'))
C
DO 40 I = 1, 61
DO 20 J = 1, 80
LINE(J) = ISPAC
20 CONTINUE
LINE(40) = IBAR
C
A = (I-1)*6.
R = A*PI/180.
SA = SIN(R)
J = 40 + IFIX(39.*SA + 0.5)
LINE(J) = ISTAR
C
WRITE(3,30) A, R, SA, (LINE(J), J = 1, 80)
30 FORMAT(1X, F5.0, F7.4, F8.4, 1X, 80A1)
40 CONTINUE
CALL EXIT
END
// XEQ
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