Computing History · Cluster
Mainframe Era
Batch systems and commercial computing.
- 01 How a Resident Monitor Chained Jobs Without an Operator The loop that read a control card, loaded the named program, and took control back when the job ended, and why an interval timer was required to make that loop reliable.
- 02 Zone Bits and Why EBCDIC Letters Are Not Contiguous How a byte splits into a zone nibble and a digit nibble, why that layout leaves gaps inside the alphabet, and what the gaps cost in collation and character-set conversion.
- 03 Packed and Zoned Decimal: Sign Nibbles and Decimal Arithmetic How decimal numbers are laid out two digits to a byte with the sign folded into the last nibble, and why the format permits decimal addition without a binary round trip.
- 04 Blocking Records on Magnetic Tape and the Cost of the Interblock Gap Why tape stores records in blocks separated by blank gaps, how block size trades tape capacity against buffer memory, and what tape marks and labels do that a gap cannot.
- 05 Channel Programs: How a Mainframe Moved Data Without the CPU The command word format a channel executes, how chaining turns a list of commands into one operation, and why the channel is a separate processor rather than a DMA engine.
- 06 Storage Keys and Region Boundaries in Multiprogrammed Batch How a four-bit key attached to every 2 KB block of storage lets one batch partition be protected from another, and what the key cannot protect.
- 07 Spooling: Turning Unit-Record Devices into Disk Files How simultaneous peripheral operations on line decouple card reading from job execution, what a spool data set must contain, and why the queue becomes the scheduler.
- 08 Dynamic Address Translation and the 16 MB Line How a two-level segment and page table turns a 24-bit virtual address into a real one, why the page tables themselves had to live in real storage, and what the 16 MB ceiling forced.
- 09 Job Classes, Initiators, and How a Batch Queue Gets Ordered Why a batch scheduler separates jobs into classes consumed by independent initiators, what an initiator costs in storage, and how starvation and throughput pull against each other.
- 10 Checkpoint and Restart: Making a Multi-Hour Batch Job Resumable What a checkpoint must capture for a job to continue correctly, why sequential files need repositioning information rather than byte counts, and how generation data sets make reruns safe.