Would he have made those same comments to resist going from 16 to 32 bit?
Hell, why not stick with 8 bit? We can just optimize everything to work on that, right?
Hell, why not stick with 8 bit? We can just optimize everything to work on that, right?
Look at GUID partition tables. With MBR, we had to hobble along with only a byte to identify partition types. Now we have 128 bits. We can finally support more filesystem kinds now than there are atoms in the Sun, all in one system installation, and the bootloader just has to look at the GUID. A 32 bit "fourcc" partition label clearly wouldn't have been enough.
A 32 bit "fourCC" would be more than adequate. It could even be constrained just to readable characters, like LNXF (Linux Filesystem) and LNXS (Linux Swap).
If another OS happens to use LNXF for something, and you have that OS in the same darn system, it doesn't matter. You just don't have that "foreign" LNXF in your /etc/fstab, and likewise it doesn't have the Linux ones in its equivalent of /etc/fstab.
The only thing that needs a clash-free label is the EFI boot partition, so the boot firmware can unambiguously identify all these partitions on all attached devices and offer them as boot options.
If the argument you want to make is that they are of no consequence, then you need to answer why your proposal of still doing something is warranted.
Why not a nibble and just use the other 4 bits for flags?
The point of this line of questioning is you're quibling over bytes which definitely don't matter in any modern context, at the expense of masses of extra management complexity to try and avoid day-to-day problems when people want to stand up new systems.
With GPT, if I want to make a new filesystem type for some application, I just generate a GUID and it will not collide without me needing to coordinate with anyone.
16 bytes is an obvious example of the "second system effect" described by Fred Brooks in Mythical Man Month.
The fdisk utility now reduces the GUIDs to one byte codes that refer to the GUIDs. For instance, I remember that 29 is Linux RAID (previously FD). Will 29 always be Linux RAID everywhere? Probably not.
> With GPT, if I want to make a new filesystem type for some application ...
Four bytes could have an ample reserved range for local use by hobbyists.
Broad recognition of the code only matters if the application is very widely deployed.
Wrong (for x86-16 vs. x86-32). Just use an operand-size size override prefix (0x66) with your 16 bit real mode ALU (in this case 'add') instruction to make it a 32 bit ALU instruction. Works from 80386 on, where the 32 bit registers were introduced.
The one thing I found absurd with RISC-V is the 128bit variant. Most 64bit processors today don't even support a full 64bit virtual address space do they?
Except when they don't. Everyone already forgot tweet number 2147483648? :) https://techcrunch.com/2009/06/12/all-hell-may-break-loose-o...
My interpretation of the shift from < 32 bits into 32 bits is: before we had do do crazy things to algorithms we used to fit in those address spaces. When we transitioned to 32 bits, we didn't have to do that anymore.
So the question might be are there any surprising workarounds in the code because you're only dealing with 32 bit code where if you had 64 bits you could write some more elegant solution.
The only other example I can think of is the general "problem" of large databases. There's just a lot more paging and churn that has to happen in a 32-bit address space. Many NoSQL databases in particular have a memory model of mmap'ing an entire database, which runs into a hard limit on 32-bit address space.
In a 16-bit address space (64K), you hit the 16-bit limit _all the time_. Even a moderately sized text document will be bigger than 64K... and that's before considering images, videos, large data sets, etc.
32-bit takes you out to 4GB, which is much more likely to hold a typical working set, so the argument to go to 64-bit is much less pressing.
"why not stick with 8 bit?"
This conversation is about the size of the address space, not the machine word size. To my knowledge, there were no serious machines of any sort that were limited to an 8-bit address space. (Maybe something homebrew or embedded.) The closest I can think of is the 6502's preference for putting values in the zero page (which was 256 bytes).
Depends on the way 16 bit is implemented. For example x86-16 uses segmented memory - enabling adressing of a little bit more (including High Memory Area) than 1 MiB of memory. The Z180 uses as far as I know a MMU (but not completely sure). Another approach that is/was in common use is to use bank switching.
Depending on the kind of algorithm that you use this can make the coding much more complicated or can also be no problem, because the scheme that is used to address more memory than 2^16 bytes fits the algorithm quite natural.
One interesting hack for example when coding in real mode (x86-16) that I read about is rather to use some clever sharing of bits between the segment register value and segment index:
- One scheme is to consider the value of the used segment register as a pointer to a 16 byte block of memory and use the segment index to adress the specific byte in this block (with an option to increase the index "a little bit" if you want to go further)
- Another scheme is to (mostly) use only the 4 highest bits of the segment register (and zero all the other ones).
This only works in real mode, where the segment is shifted and directly added to the offset. In protected mode, it goes through a selector table. This can be made to work too, but it requires tiled allocations of segments with known delta between each segment. This is what __ahincr was about, if you remember it from the Win16 days.
Of course this is true. You wrote further above:
> In a 16-bit address space (64K), you hit the 16-bit limit _all the time_.
I wanted to outline that whether this is a problem or not depends a lot on the concrete 16 bit architecture.
I'd be interested to hears... I really can't. Probably the most capable architecture I'm familiar with that has a native 16-bit pointer type is the 80286, which provides 24-bit physical addressing, virtualizatoin, protections, etc. Even then, at least on Windows, key local heaps within the OS were confined to 64K, the default text editor was confined to a segment... writing image processing tools (which I did) required special handling for all but the smallest scale workloads. These all added to developer workload and reduced system capacity in unfortunate ways.
I get what you're saying that there are exceptions and hacks that make it possible to work within these limitations, but my point is that you have to care about them on 16-bit, and most of the time you really don't on 32-bit. My thesis for why that is goes back to what I was saying initially about the size of the core data types people tend to manipulate.
(And this goes back to the reason I posted in the first place, which was to explain the relative difference in motivation between the 16->32 switch and the 32->64 switch.)
Your question implies that you want one piece > 64 KiB of flat memory. With this you already stated a very strong implicit assumption about the data layout and the kind of algorithm that you want to use. My point rather is: Consider the capabilities that the 16b machine has and try to fit the data representation and algorithms that you use around it instead of wining about lack of machine capabilities. One will often find a solution using clever tricks that one would not have considered otherwise, which will often turn out to be surprisingly elegant and much better than the "naive" solution.
This way to program is of course nothing for the kind of programmer that want to write an unelegant and just working program in a short amount of time, I know. :-)
I do hear you, but one of the things I love about virtually all modern hardware is just how much capability it puts within the reach of totally naive and quick development strategies. If I can inelegantly solve two or three problems in the same time I can elegantly solve one, then that strikes me as a net win (at least for the people that need problems solved more than code written.)
I don't mind pushing the hardware and searching for elegance, but I'd rather be forced into it by the necessities of the problem I'm trying to solve.