3 ms·

Fantastic work by Ken yet again. It's striking how many of the early microprocessors shipped with bugs. The 6502 and 8086 both did and it was an even bigger pr

Fantastic work by Ken yet again. It's striking how many of the early microprocessors shipped with bugs. The 6502 and 8086 both did and it was an even bigger problem for processors like the Z8000 and 32016 where the bugs really helped to hinder their adoption. And the problem of bugs was a motivation for both the Berkeley RISC team and for Acorn ARM team when choosing RISC.

adrian_b 4y ago
All the current processors are shipping with known bugs, including all Intel and AMD CPUs and all CPUs with ARM cores, also including even all the microcontrollers with which I have ever worked, regardless of manufacturer. The many bugs (usually from 20 to 100) of each CPU model are enumerated in errata documents with euphemistic names like "Specification Update" of Intel and "Revision Guide" of AMD. Some processor vendors have the stupid policy of providing the errata list only under NDA. Many of the known bugs have workarounds provided by microcode updates, a few are scheduled to be fixed in a later CPU revision, some affect only privileged code and it is expected that the operating system kernels will include workarounds that are described in the errata document, and many bugs have the resolution "Won't fix", because it is considered that they either affect things that are not essential for the correct execution of a program, e.g. the values of the performance counters or the speed of execution, or because it is considered that those bugs happen only in very peculiar circumstances that are unlikely to occur in any normal program. I recommend the reading of some of the "Specification Update" documents of Intel, to understand the difficulties of designing a bug-free CPU, even if much of the important information about the specific circumstances that cause the bugs is usually omitted.

3 ms·

Fantastic work by Ken yet again. It's striking how many of the early microprocessors shipped with bugs. The 6502 and 8086 both did and it was an even bigger pr

by klelatti 4y ago

adrian_b 4y ago
All the current processors are shipping with known bugs, including all Intel and AMD CPUs and all CPUs with ARM cores, also including even all the microcontrollers with which I have ever worked, regardless of manufacturer. The many bugs (usually from 20 to 100) of each CPU model are enumerated in errata documents with euphemistic names like "Specification Update" of Intel and "Revision Guide" of AMD. Some processor vendors have the stupid policy of providing the errata list only under NDA. Many of the known bugs have workarounds provided by microcode updates, a few are scheduled to be fixed in a later CPU revision, some affect only privileged code and it is expected that the operating system kernels will include workarounds that are described in the errata document, and many bugs have the resolution "Won't fix", because it is considered that they either affect things that are not essential for the correct execution of a program, e.g. the values of the performance counters or the speed of execution, or because it is considered that those bugs happen only in very peculiar circumstances that are unlikely to occur in any normal program. I recommend the reading of some of the "Specification Update" documents of Intel, to understand the difficulties of designing a bug-free CPU, even if much of the important information about the specific circumstances that cause the bugs is usually omitted.