This is backwards from manual right-to-left methods and more complicated, but it allowed all result writing to be suppressed in overflow cases.
To compensate for this, the B3700/B4700 generation used semiconductor main memory that was faster but more expensive and power hungry than the DRAM used in competing machines.
An attempted redesign in 1975 of the address space was called MS-3 for "Medium Systems 3rd Generation", but that project was cancelled.
[4][5] Machines before the B2900 allowed input numbers with 'undigit' values above 9, but arithmetic on this gave unspecified results.
[6] In the B4900 and later machines, integer operations of 10 digits or fewer were now handled in parallel; only longer operands continued to use the serial method.
Later Medium Systems machines added an accumulator register and accumulator/memory instructions using 32-bit, 7-digit integers and 48-bit or 80-bit floating point values, all aligned on 16-bit word boundaries.
It shared many architectural features with the MCP of Burroughs' Large Systems stack machines, but was entirely different internally, and was coded in assembly language, not an ALGOL derivative.
Programs had separate address spaces dynamically relocated by a base register, but otherwise there was no virtual memory; no paging and no segmentation.
But this turned out to be impractical to maintain after software changes, and better results were consistently achieved with a totally randomized layout of all MCP overlays.
MCP allowed programs to communicate with each other via core-to-core transmissions (CRCR) or by using storage queues (STOQ), implemented as system calls using the BCT instruction and exposed to the languages (COBOL FILL FROM/INTO).
This was unheard of except on the very largest IBM System/360 systems of the time, and even then it was a major operational headache to manage the interactions of the multiple program streams.
Larger Medium Systems processors supported major data center activities for banks and other financial institutions, as well as many businesses and government customers.
With the Medium System, a computer could be simultaneously running a batch payroll system, inputting bank checks on a MICR reader sorter, compiling COBOL applications, supporting on-line transactions, and doing test runs on new applications (colloquially called 'the mix', as the console command 'MX' would shows that jobs were executing).
Tape was a major storage medium on these computers, in early days it was often used for father-son batch updating; with additional disk becoming cheaper as time moved on it became relegated as a library/backup device that contained all the data files and sometimes the program files (using the MFSOLT utility) for a particular application or customer/client.