using overlay in System/7 and sealed cartridges in it

[shaharhada]

The advanced (for the time) seminconductor memory made the machine fast but also expensive, so a lot of work went into minimizing the typical memory footprint of an application before deployment. The development tools normally ran on IBM's 360 computer system and the program image was the downloaded to a System/7 in a development lab by serial link. Up until 1975 at least it was rare to use disk overlays for the programs, with no support for that in the software tools. Hard disks, in the IBM Dolphin line of sealed cartridges, were available but expensive and were generally used as file systems storing data and executable programs (thereby eliminating the need to rely on the paper tape reader for system boot-up).

From Wikipedia:
https://en.wikipedia.org/wiki/IBM_System/7

What is line of sealed cartridges?
What is to overlay (for the programs)? How it done in System/7

 

[hotaru.hino]

A sealed cartridge in this context is a platter (or several) coated with magnetic material to be used as a storage drive. Think of them like floppy disks that came later, only larger and made with large disks. It's sealed likely to keep them clean.

An overlay is a table that translates what location the program wants to access in storage to where that location actually is. If you don't use an overlay, this limits you to a particular model or capacity of storage drives.

 

[USAFRet]

The IBM Dolphin

https://en.wikipedia.org/wiki/History_of_IBM_magnetic_disk_drives
IBM 5444

The IBM 5444 was announced September 1969 as part of System/3. Developed at IBM's Hursley, England, laboratory under code name Dolphin[55] it used the 5440 disk cartridge. The cartridge in turn contained one 14-inch disk. There were three models:[60]

Model 1 has one fixed disk and one removable disk each with 100 tracks per surface for a disk cartridge capacity of 1.23 MB
Model 2 has one fixed disk and one removable disk each with 200 tracks per surface for a disk cartridge capacity of 2.46 MB
Model 3 has only one removable disk with 200 tracks per surface for a disk cartridge capacity of 2.46 MB