Storage

What controller will you use?

Early IDE (IDE, ATA-1)

• IDE for 16bit ISA controllers, connects IDE storage devices directly to the ISA bus
• Few storage devices from this period supported the DMA modes.
• Processors <= 386 are frequently CPU bound when doing PIO
• Modern storage devices seem to reliably fall back to ATA-1

Early EIDE (Ultra ATA, UDMA/33 )

• Common between 1993-1998
• Mid to Late 486, Early Pentiums
• 80 connector IDE cables recommended but not required
• Noticeable performance improvements when using multiword IO & DMA modes.
• Controllers from this period sometimes have trouble negotiating with SD-IDE adapters and DOMs
• Storage devices from this period sometimes have trouble working in LBA mode with newer controllers
• https://en.wikipedia.org/wiki/PCI_IDE_ISA_Xcelerator

Mature ATA (ATA-66, ATA-100 & ATA-133)

• Common between 1999-2010
• 80 connector IDE cables required to negotiate speeds faster than ATA/33. If using a DOM or CF adapter with a female connector and no cable, Pin #34 needs to be grounded
• Not a large performance difference between ATA-66 & ATA-133 for most storage devices
• Controllers connected via PCI bus see a small performance drop compared to a IHA or Vlink attached controllers
• UDMA modes are necessary to achieve peak speeds in most cases
• Most motherboards BIOS I/O routines are not able to take advantage of DMA
• https://en.wikipedia.org/wiki/I/O_Controller_Hub

IDE and BIOS Limits & Incompatibilities

• 528 MB limit - BIOS before July 1994 rarely support drives over 528MB (Cylinders <= 1024 (BIOS), Heads <= 16 (ATA0), Sectors <= 63 (BIOS))
• 2015 MB limit - BIOS before May 1996 rarely support drives larger than 2015 MB (Cylinders <= 4095 (BIOS), Heads <= 16 (ATA0), Sectors <= 63 (BIOS))
• 3277 MB limit - Phoenix BIOS 4.03 and 4.04 lock when a drive is configured with a capacity over 3277 MB.
• 4.2 GB limit - BIOS before February 1997 have the first ECHS (Extended CHS) limit. DOS and Windows 95/98 cannot handle 256 heads. 'Large' mode in the BIOS produces an alternate geometry by doubling the number of heads and halving the number of cylinders shown to DOS to keep the cylinders below 1024. This method stops working at 4032 MB (1024 cylinders, 128 heads, 63 sectors) if the drive reports 16 heads.
• 7.9 GB limit - Other BIOS from this period had a Revised ECHS limit. 'Large' mode in the BIOS by presenting an alternate geometry using multiples of 15 heads so that 240 heads can be presented as the max alternate geometry. This method stops working at 7560 MB (C=1024, H=240, S=63)
• 8.4 GB limit - Final ECHS limit - Bios geometry translation uses head value from the sequence 16, 32, 64, 128, 255 to present an alternate geometry up to (C=1024, H=255, S=63). Hard drives larger than 8.4GB report a geometry of C=16383,H=16,S=63 to indicate that they are larger than can be described using ECHS geometry translation)
• 33.8 GB limit - BIOS before August 1999 often stored the cylinders as a 16 bit value, so the max cylinders was 65535
• 137.4 GB limit - BIOS before September 2001 only used ATA-5, which used 28 bits to identify each LBA sector, limiting drive capacity to 137GB. ATA-6 extended this to 48 bits. Hard drives over 137.4 GB should report an LBA capacity of 0xfffffff sectors and report the actual value in the 48-bit field.
• Early IDE drives do not always work correctly with mature LBA controllers and must be manually set to 'CHS' mode in order to operate correctly.

Modern Storage for Retro Computers

SD to IDE Pros

• SD Cards are cheap
• Quick response on small reads and writes

CF (Compact Flash) Pata DOM (Disk on Module) Sata Drive mSata M2 Sata USB to IDE Sata SSD Sata DOM

Common Legacy Storage

Sata DOM