DEC STD 144

This document (DEC STD 144) establishes a combined hardware and software standard for identifying and handling disk sectors found to be bad during the manufacturing process of RK06, RK07, and future disk cartridges. Its primary goal is to enhance system reliability by preventing operating systems and users from attempting to access these faulty sectors.

The standard defines two primary methods for identifying bad sectors:

1. Good Sector Flag: Each sector's header contains a specific bit (bit 15 of word 2) that is cleared to zero if the sector is bad at manufacturing. Controllers are designed to detect this flag and report an error, preventing data access to that sector.
2. Bad Sector File (BSF): A comprehensive list of all manufacturing-detected bad sectors (including their cylinder, track, and sector locations) is recorded in a dedicated file on the highest-numbered track of the disk cartridge. This file also stores manufacturing information like serial numbers and is formatted for compatibility across different DEC operating systems (DECsystem 10, PDP-11, PDP-15).

Regarding operating system conformance, the standard mandates different approaches:

• Small Systems: Must use a utility to allocate bad sectors to a specific, inaccessible file whenever the disk is refreshed, ensuring users cannot access them.
• Large Systems: Are required to mark these bad sectors as "in use" during disk refresh, thereby preventing their allocation or access by users.

Importantly, the standard does not require any system to remap bad blocks, meaning users allocating contiguous space may still encounter "gaps" where bad sectors are located. It focuses solely on manufacturing-detected errors, though it reserves space for potential future extensions to handle field-detected errors. Software is prohibited from overwriting the first 10 sectors of the highest track, where this crucial information resides.