Alex_03 wrote on 2024-01-06, 02:22:
The overall consensus is that 4Mb is fine for DOS [..]
Yup. Though SmartDrive's cache can do benefit from extra memory.
The real world maximum for the cache was around 4 MB, I suppose.
With the /double_buffer setting enabled (for Windows 3.x), a bit more even.
Of course, it depends on the configuration of the PC.
If it has a CF card and a floppy drive, SmartDrive isn't so important.
If a CD-ROM drive is installed, though, SmartDrive can make a difference.
It will read ahead and cache big chunks of data (not unusual for games/ talkie titles),
so the gameplay won't stutter and the drive won't "squeak" all the time because of head movement
(without a cache, every file needs to be re-read upon access).
Anyway, it's just a footnote, maybe.
I didn't use SmartDrive back in the 90s, when I had my 286 w/ 4MB of RAM.
The CD-ROM drive was a single-speed type (via PAS16 SCSI) and access was quite jerky, but I could live with it.
Also, a caching controller can do the same thing as SmartDrive, maybe. For HDDs/floppy drives, at least.
Edit: As a workaround, a modern CD-ROM drive can be used instead. It has a bigger buffer than a period-correct drive.
With CDSPEED utility, many CD-ROM drives cam be set to a slower, constant speed.
That way, they won't spin up/down all the time (causes jerky access).
https://www.sac.sk/files.php?d=14&p=8
Edit: Again, 4 MB is usually fine.
OS/2 starts to feel comfortable with 8 MB.
More than ~10 MB aren't useful, either.
The 15-16 MB area is the end of ISA address space and sometimes used by certain things as an i/o space
(16-Bit ISA VGAs, network cards etc). It's comparable to the 640KB-1MB area, maybe.
Windows 3.x doesn't really need more than 4MB, but it can benefit from large empty RAM.
That's because of memory fragmentation and the Windows memory management in general.
Windows 3.x wants free memory that's "contiguous",
also in parts because it's using a shared memory model and fixed starting points for the applications (they use relocation tables).
Long story short, with more free memory (more headroom), Windows doesn't need to shuffle around memory so much.
Edit: I did forget. SmartDrive or MSCDEX may also support EMS.
So someone can install a dedicated EMS board, which is separate from PC memory.
Edit: Pictures
PS: It's just meant as an orientation. A small cache (say 512KB) may do good enough already.
It just came to mind because I lived without SmartDrive for a long time, so the difference with/without is more apparent to me now.
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