IBM System/360 Model 44
| Company type | Computer model |
|---|---|
| Industry | Computer hardware |
| Founded | August 16, 1965 |
| Defunct | September 1973 |
| Products | Scientific computation, real-time computing, process control, numerical control computer |
The IBM System/360 Model 44 represents a tailored edition within the IBM System/360 series, engineered specifically for applications in scientific computation, real-time computing, process control, and numerical control (NC).
Introduced on August 16, 1965, and discontinued by September 1973, this model excluded the typical storage-to-storage character and decimal instruction sets but compensated with an "extended instruction set" to fulfill those functions. It incorporated four exclusive instructions: Change Priority Mask (CHPM), Load PSW Special (LPSX), Read Direct Word (RDDW), and Write Direct Word (WRDW).
Memory configurations spanned from 32 KB up to 256 KB, featuring a rapid 1 μs access speed, aligning more closely with the high-end IBM System/360 Model 65 than the Model 50. Storage protection was offered as an optional feature. General purpose registers were commonly housed in a non-addressable core storage segment known as "bump storage," with an optional Solid Logic Technology (SLT) version reducing access latency to 0.25 μs.
One notable innovation was the variable-length precision floating point arithmetic, which permitted users to adjust the mantissa length of extended floating-point numbers between 32 and 56 bits via a rotary switch on the front panel—allowing a trade-off between precision and processing speed while preserving a fixed 64-bit size in memory.
The Model 44 optionally supported six external interrupt lines. Its direct word capability allowed complete 32-bit data transfers between external peripherals and main memory, exceeding the standard byte-wise transfers found in other System/360 variants. The direct data channel enabled swift, word-level data movement at speeds reaching up to 4 MiB/s through conventional I/O instructions.
With its priority interrupt functionality, the system expanded interrupt levels from five to thirty-two, incorporating advanced masking and prioritization controlled by the CHPM and LPSX instructions. This facilitated dynamic management of interrupts and effective processing of multiple simultaneous external signals essential for real-time operations and process control environments.
Write Direct Word ('B4'x): WRDW D1(B1),I2
Read Direct Word ('B5'x): RDDW D1(B1),I2
Load PSW Special ('B2'x): LPSX D1(B1),I2
I2 must be zero; it is reserved.
Change Priority Mask ('B3'x): CHPM D1(B1),I2
The higher-order bits specify mask operations:
(mask bit) (cancel bit) Function 1 0 Activate levels identified by 1 bits 0 0 Deactivate levels identified by 0 bits 0 1 Cancel levels identified by 1 bits 1 1 Cancel and activate levels identified by 1 bits
Peripherals
The Model 44 accommodates one standard along with two high-speed System/360 multiplexer channels, complemented by built-in adapters for both the single disk storage device and the console 1052 printer/keyboard.
A unique aspect is its built-in single disk storage unit employing the IBM 2315 cartridge, providing removable disk capacity of 1,171,200 bytes integrated within the CPU. An optional second integrated drive may be added. The Model 44 Programming System (M44PS) leverages this drive as its system residence medium.
Software
The Model 44 Programming System comprises a supervisor, various utility applications, an assembler, a FORTRAN IV compiler, along with a collection of scientific subroutine libraries.