You're thinking very much in terms of a PC architecture. Many components of the mainframe including a lot of the I/O hardware and some instructions in the assembly language itself are record oriented, and within reasonable limits operate on an entire record at once. It's not that big of a jump to go from entire records being atomic operations to at least speaking about entire transactions being the basic, atomic units of computation in the system.
Like a row in a table. I/O instructions in S/360 (as I recall) assembler would fetch an entire record in a single instruction / cycle (the I/O devices are radically different and would support this - it wasn't just syntactic sugar around reading a word or byte at a time). So the time to read in a record, perform some operations and write a record back out is actually much more predictable based on clock speed than it sounds like it would be to someone from a PC background.
Row and table would be the database terminology. In mainframes you have records in datasets, but they're the same thing: tuples of fields. It's just that in a mainframe to maximize throughout a lot of the work like dealing with natively supported data formats is offloaded to special I/O controllers, which makes it easier to work with via low-level assembly instructions.
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You're thinking very much in terms of a PC architecture. Many components of the mainframe including a lot of the I/O hardware and some instructions in the assembly language itself are record oriented, and within reasonable limits operate on an entire record at once. It's not that big of a jump to go from entire records being atomic operations to at least speaking about entire transactions being the basic, atomic units of computation in the system.
Define a record.
Also can you elaborate more on how ASM instructions can be record oriented?
Like a row in a table. I/O instructions in S/360 (as I recall) assembler would fetch an entire record in a single instruction / cycle (the I/O devices are radically different and would support this - it wasn't just syntactic sugar around reading a word or byte at a time). So the time to read in a record, perform some operations and write a record back out is actually much more predictable based on clock speed than it sounds like it would be to someone from a PC background.
to the CPU, what's a row and what's a table in this context.
Row and table would be the database terminology. In mainframes you have records in datasets, but they're the same thing: tuples of fields. It's just that in a mainframe to maximize throughout a lot of the work like dealing with natively supported data formats is offloaded to special I/O controllers, which makes it easier to work with via low-level assembly instructions.